| Message ID | 20220620143129.1772880-3-trini@konsulko.com |
|---|---|
| State | Superseded |
| Delegated to: | Heinrich Schuchardt |
| Headers | show |
| Series | [1/3] doc: environment: Drop u-boot_addr_r | expand |
On Mon, 20 Jun 2022 at 08:32, Tom Rini <trini@konsulko.com> wrote: > > Start by elaborating on what some of our constraints tend to be with > image location values, and document where these external constraints > come from. Provide a new subsection, an example based on the TI ARMv7 > OMAP2PLUS families of chips, that gives sample values and explains why > we use these particular values. This is based on what is in > include/configs/ti_armv7_common.h as of fb3ad9bd923d ("TI: Add, use a > DEFAULT_LINUX_BOOT_ENV environment string") as this contains just the > values referenced in this document now and not some of the further > additions that are less generic. > > Signed-off-by: Tom Rini <trini@konsulko.com> > --- > doc/usage/environment.rst | 39 +++++++++++++++++++++++++++++++++++++++ > 1 file changed, 39 insertions(+) Reviewed-by: Simon Glass <sjg@chromium.org> > > diff --git a/doc/usage/environment.rst b/doc/usage/environment.rst > index a9a4702632d2..f70ccd6a58ee 100644 > --- a/doc/usage/environment.rst > +++ b/doc/usage/environment.rst > @@ -404,6 +404,42 @@ device tree blob fdtfile fdt_addr_r fdt_addr > ramdisk ramdiskfile ramdisk_addr_r ramdisk_addr > ================= ============== ================ ============== > > +When setting the RAM addresses for `kernel_addr_r`, `fdt_addr_r` and > +`ramdisk_addr_r` there are several constraints to keep in mind. When booting > +Linux, the `Booting ARM Linux`_ and `Booting AArch64 Linux`_ documents lay out > +the requirements for booting all ARM platforms, including both alignment and > +where within memory various things must be. These guidelines tend to also be > +correct for other OSes and unless specifically contradicted by documentation > +specific to another architecture, are good rules to follow for other > +architectures as well. > + > +Example Image locations > +^^^^^^^^^^^^^^^^^^^^^^^ > + > +If we take the Texas Instruments OMAP2PLUS family of ARMv7 processors as an > +example for the above listed variables, we would do:: > + > + loadaddr=0x82000000 > + kernel_addr_r=${loadaddr} > + fdt_addr_r=0x88000000 > + ramdisk_addr_r=0x88080000 > + bootm_size=0x10000000 > + > +To explain this, we start by noting that DRAM starts at 0x80000000. A 32MiB Should it say 'We use a 32MiB' ? > +buffer from the start of memory as our default load address, and so where the > +kernel would also be loaded to. This will hopefully allow for us to have the > +whole of the compressed kernel image exist in memory above where the whole of > +the decompressed kernel image will be, and allow for a quicker boot. Next, we > +say that the device tree will be placed at 128MiB offset from the start of > +memory. This is suggested by the kernel documment as it is exceedingly > +unlikely to be overwritten by the kernel itself given other architectural > +constraints. We then allow for the device tree to be up to 512KiB in size > +before placing the ramdisk in memory. We then say that everything should be > +within the first 256MiB of memory so that U-Boot can relocate things as needed > +to ensure proper alignment. We pick 256MiB as our value here because we know > +there are very few platforms on in this family with less memory. It could be > +as high as 768MiB and still ensure that everything would be visible to the > +kernel, but again we go with what we assume is the safest assumption. > > Automatically updated variables > ------------------------------- > @@ -472,3 +508,6 @@ Implementation > -------------- > > See :doc:`../develop/environment` for internal development details. > + > +.. _`Booting ARM Linux`: https://www.kernel.org/doc/html/latest/arm/booting.html > +.. _`Booting AArch64 Linux`: https://www.kernel.org/doc/html/latest/arm64/booting.html > -- > 2.25.1 >
On 6/30/22 12:06, Simon Glass wrote: > On Mon, 20 Jun 2022 at 08:32, Tom Rini <trini@konsulko.com> wrote: >> >> Start by elaborating on what some of our constraints tend to be with >> image location values, and document where these external constraints >> come from. Provide a new subsection, an example based on the TI ARMv7 >> OMAP2PLUS families of chips, that gives sample values and explains why >> we use these particular values. This is based on what is in >> include/configs/ti_armv7_common.h as of fb3ad9bd923d ("TI: Add, use a >> DEFAULT_LINUX_BOOT_ENV environment string") as this contains just the >> values referenced in this document now and not some of the further >> additions that are less generic. >> >> Signed-off-by: Tom Rini <trini@konsulko.com> >> --- >> doc/usage/environment.rst | 39 +++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 39 insertions(+) > > Reviewed-by: Simon Glass <sjg@chromium.org> Below you want a change? > >> >> diff --git a/doc/usage/environment.rst b/doc/usage/environment.rst >> index a9a4702632d2..f70ccd6a58ee 100644 >> --- a/doc/usage/environment.rst >> +++ b/doc/usage/environment.rst >> @@ -404,6 +404,42 @@ device tree blob fdtfile fdt_addr_r fdt_addr >> ramdisk ramdiskfile ramdisk_addr_r ramdisk_addr >> ================= ============== ================ ============== >> >> +When setting the RAM addresses for `kernel_addr_r`, `fdt_addr_r` and >> +`ramdisk_addr_r` there are several constraints to keep in mind. When booting >> +Linux, the `Booting ARM Linux`_ and `Booting AArch64 Linux`_ documents lay out >> +the requirements for booting all ARM platforms, including both alignment and >> +where within memory various things must be. These guidelines tend to also be >> +correct for other OSes and unless specifically contradicted by documentation What makes you think that BSD or Haiku have the same constraints as Linux? >> +specific to another architecture, are good rules to follow for other >> +architectures as well. No. RISC-V does not have the same requirements as ARM. E.g. the initrd can be located anywhere in memory. >> + >> +Example Image locations >> +^^^^^^^^^^^^^^^^^^^^^^^ You seem not to refer to a file 'Image'. %s/Image/image/ >> + >> +If we take the Texas Instruments OMAP2PLUS family of ARMv7 processors as an >> +example for the above listed variables, we would do:: %s/we would do/we chose/ ? >> + >> + loadaddr=0x82000000 >> + kernel_addr_r=${loadaddr} >> + fdt_addr_r=0x88000000 >> + ramdisk_addr_r=0x88080000 >> + bootm_size=0x10000000 >> + >> +To explain this, we start by noting that DRAM starts at 0x80000000. A 32MiB > > Should it say 'We use a 32MiB' ? Please, mention that MAX_UNCOMP_KERNEL_SIZE = 32 MiB is ARMv7 specific. > > >> +buffer from the start of memory as our default load address, and so where the >> +kernel would also be loaded to. This will hopefully allow for us to have the %s/allow for us/allow/ >> +whole of the compressed kernel image exist in memory above where the whole of >> +the decompressed kernel image will be, and allow for a quicker boot. Next, we Please, mention that decompressor code otherwise will have to relocate the compressed kernel. >> +say that the device tree will be placed at 128MiB offset from the start of Please, mention that initrd must be * within 512 MiB (0x20000000) of the memory start on arm (which restricts initrd_high) * in a a 1 GB aligned region of size '1UL << (VA_BITS_MIN - 1)' that includes the kernel on arm64 On RISC-V such a limitation does not exist. >> +memory. This is suggested by the kernel documment as it is exceedingly %s/documment/document >> +unlikely to be overwritten by the kernel itself given other architectural >> +constraints. We then allow for the device tree to be up to 512KiB in size >> +before placing the ramdisk in memory. We then say that everything should be >> +within the first 256MiB of memory so that U-Boot can relocate things as needed >> +to ensure proper alignment. We pick 256MiB as our value here because we know If the load address ranges occupy the first 256 MiB, where will be the space for relocation on a 256 MiB board? Without mentioning initrd_high this paragraph is incomplete. >> +there are very few platforms on in this family with less memory. It could be >> +as high as 768MiB and still ensure that everything would be visible to the >> +kernel, but again we go with what we assume is the safest assumption. A section per architecture clearly naming the architecture specific restrictions of Linux would be much more helpful. Best regards Heinrich >> >> Automatically updated variables >> ------------------------------- >> @@ -472,3 +508,6 @@ Implementation >> -------------- >> >> See :doc:`../develop/environment` for internal development details. >> + >> +.. _`Booting ARM Linux`: https://www.kernel.org/doc/html/latest/arm/booting.html >> +.. _`Booting AArch64 Linux`: https://www.kernel.org/doc/html/latest/arm64/booting.html >> -- >> 2.25.1 >>
On Sun, Jul 10, 2022 at 02:26:04PM +0200, Heinrich Schuchardt wrote: > On 6/30/22 12:06, Simon Glass wrote: > > On Mon, 20 Jun 2022 at 08:32, Tom Rini <trini@konsulko.com> wrote: > > > > > > Start by elaborating on what some of our constraints tend to be with > > > image location values, and document where these external constraints > > > come from. Provide a new subsection, an example based on the TI ARMv7 > > > OMAP2PLUS families of chips, that gives sample values and explains why > > > we use these particular values. This is based on what is in > > > include/configs/ti_armv7_common.h as of fb3ad9bd923d ("TI: Add, use a > > > DEFAULT_LINUX_BOOT_ENV environment string") as this contains just the > > > values referenced in this document now and not some of the further > > > additions that are less generic. > > > > > > Signed-off-by: Tom Rini <trini@konsulko.com> > > > --- > > > doc/usage/environment.rst | 39 +++++++++++++++++++++++++++++++++++++++ > > > 1 file changed, 39 insertions(+) > > > > Reviewed-by: Simon Glass <sjg@chromium.org> > > Below you want a change? Yes, often Simon does that (and it's fine) to both offer a tag but if another iteration is needed to make a minor adjustment to some wording or another, or to make when applying. Which is fine with me. > > > diff --git a/doc/usage/environment.rst b/doc/usage/environment.rst > > > index a9a4702632d2..f70ccd6a58ee 100644 > > > --- a/doc/usage/environment.rst > > > +++ b/doc/usage/environment.rst > > > @@ -404,6 +404,42 @@ device tree blob fdtfile fdt_addr_r fdt_addr > > > ramdisk ramdiskfile ramdisk_addr_r ramdisk_addr > > > ================= ============== ================ ============== > > > > > > +When setting the RAM addresses for `kernel_addr_r`, `fdt_addr_r` and > > > +`ramdisk_addr_r` there are several constraints to keep in mind. When booting > > > +Linux, the `Booting ARM Linux`_ and `Booting AArch64 Linux`_ documents lay out > > > +the requirements for booting all ARM platforms, including both alignment and > > > +where within memory various things must be. These guidelines tend to also be > > > +correct for other OSes and unless specifically contradicted by documentation > > What makes you think that BSD or Haiku have the same constraints as Linux? Because of what I said, and experience? Now, one may be a subset of another, but that still means it will work for both. This is intended to be general best practices. If you follow this then it's likely anything else will work too. The danger comes from trying to optimize the sizes to be as small as possible, rather than as large/flexible as will likely work anywhere. I will try and expand on that idea in the next iteration. > > > +specific to another architecture, are good rules to follow for other > > > +architectures as well. > > No. RISC-V does not have the same requirements as ARM. E.g. the initrd > can be located anywhere in memory. Please point to documentation that confirms that, and some otherwise bad examples that actually work. > > > + > > > +Example Image locations > > > +^^^^^^^^^^^^^^^^^^^^^^^ > > You seem not to refer to a file 'Image'. > > %s/Image/image/ OK. > > > + > > > +If we take the Texas Instruments OMAP2PLUS family of ARMv7 processors as an > > > +example for the above listed variables, we would do:: > > %s/we would do/we chose/ ? Either? I don't see it mattering either way. > > > + > > > + loadaddr=0x82000000 > > > + kernel_addr_r=${loadaddr} > > > + fdt_addr_r=0x88000000 > > > + ramdisk_addr_r=0x88080000 > > > + bootm_size=0x10000000 > > > + > > > +To explain this, we start by noting that DRAM starts at 0x80000000. A 32MiB > > > > Should it say 'We use a 32MiB' ? > > Please, mention that MAX_UNCOMP_KERNEL_SIZE = 32 MiB is ARMv7 specific. Sorry? As I understood it last, the maximum size was something like 96MiB before you have to employ some funky tricks. > > > +buffer from the start of memory as our default load address, and so where the > > > +kernel would also be loaded to. This will hopefully allow for us to have the > > %s/allow for us/allow/ > > > > +whole of the compressed kernel image exist in memory above where the whole of > > > +the decompressed kernel image will be, and allow for a quicker boot. Next, we We use 32MiB for the reason I said here. Which is only a slight rewording of the arm32 Linux booting document, and the section starts out by saying this is an example for ARMv7 platforms. > Please, mention that decompressor code otherwise will have to relocate > the compressed kernel. I'm not sure. Perhaps it would be good to also link to some of the articles expanding upon how Linux on ARM32 boots, as part of more general documentation, rather than a specific example here. > > > +say that the device tree will be placed at 128MiB offset from the start of > > Please, mention that initrd must be > > * within 512 MiB (0x20000000) of the memory start on arm > (which restricts initrd_high) > * in a a 1 GB aligned region of size '1UL << (VA_BITS_MIN - 1)' that > includes the kernel on arm64 No, because this is not intended to list every constraint on ARM32 (nor arm64, which would benefit from an example that's not TI, as TI arm64 platforms share the same base address for memory). > On RISC-V such a limitation does not exist. I do wish that RISC-V had a similar document to ARM/ARM64, in Linux. > > > +memory. This is suggested by the kernel documment as it is exceedingly > > %s/documment/document > > > > +unlikely to be overwritten by the kernel itself given other architectural > > > +constraints. We then allow for the device tree to be up to 512KiB in size > > > +before placing the ramdisk in memory. We then say that everything should be > > > +within the first 256MiB of memory so that U-Boot can relocate things as needed > > > +to ensure proper alignment. We pick 256MiB as our value here because we know > > If the load address ranges occupy the first 256 MiB, where will be the > space for relocation on a 256 MiB board? Without mentioning initrd_high > this paragraph is incomplete. You don't need initrd_high / fdt_high when bootm_size is used. Maybe that needs to be clearer in this paragraph and also the rest of the documentation. > > > +there are very few platforms on in this family with less memory. It could be > > > +as high as 768MiB and still ensure that everything would be visible to the > > > +kernel, but again we go with what we assume is the safest assumption. > > A section per architecture clearly naming the architecture specific > restrictions of Linux would be much more helpful. I did ask for further explained examples as it would indeed be good to have at least one per architecture.
On 7/10/22 18:17, Tom Rini wrote: > On Sun, Jul 10, 2022 at 02:26:04PM +0200, Heinrich Schuchardt wrote: >> On 6/30/22 12:06, Simon Glass wrote: >>> On Mon, 20 Jun 2022 at 08:32, Tom Rini <trini@konsulko.com> wrote: >>>> >>>> Start by elaborating on what some of our constraints tend to be with >>>> image location values, and document where these external constraints >>>> come from. Provide a new subsection, an example based on the TI ARMv7 >>>> OMAP2PLUS families of chips, that gives sample values and explains why >>>> we use these particular values. This is based on what is in >>>> include/configs/ti_armv7_common.h as of fb3ad9bd923d ("TI: Add, use a >>>> DEFAULT_LINUX_BOOT_ENV environment string") as this contains just the >>>> values referenced in this document now and not some of the further >>>> additions that are less generic. >>>> >>>> Signed-off-by: Tom Rini <trini@konsulko.com> >>>> --- >>>> doc/usage/environment.rst | 39 +++++++++++++++++++++++++++++++++++++++ >>>> 1 file changed, 39 insertions(+) >>> >>> Reviewed-by: Simon Glass <sjg@chromium.org> >> >> Below you want a change? > > Yes, often Simon does that (and it's fine) to both offer a tag but if > another iteration is needed to make a minor adjustment to some wording > or another, or to make when applying. Which is fine with me. > >>>> diff --git a/doc/usage/environment.rst b/doc/usage/environment.rst >>>> index a9a4702632d2..f70ccd6a58ee 100644 >>>> --- a/doc/usage/environment.rst >>>> +++ b/doc/usage/environment.rst >>>> @@ -404,6 +404,42 @@ device tree blob fdtfile fdt_addr_r fdt_addr >>>> ramdisk ramdiskfile ramdisk_addr_r ramdisk_addr >>>> ================= ============== ================ ============== >>>> >>>> +When setting the RAM addresses for `kernel_addr_r`, `fdt_addr_r` and >>>> +`ramdisk_addr_r` there are several constraints to keep in mind. When booting >>>> +Linux, the `Booting ARM Linux`_ and `Booting AArch64 Linux`_ documents lay out >>>> +the requirements for booting all ARM platforms, including both alignment and >>>> +where within memory various things must be. These guidelines tend to also be >>>> +correct for other OSes and unless specifically contradicted by documentation >> >> What makes you think that BSD or Haiku have the same constraints as Linux? > > Because of what I said, and experience? Now, one may be a subset of > another, but that still means it will work for both. This is intended > to be general best practices. If you follow this then it's likely > anything else will work too. The danger comes from trying to optimize > the sizes to be as small as possible, rather than as large/flexible as > will likely work anywhere. I will try and expand on that idea in the > next iteration. > >>>> +specific to another architecture, are good rules to follow for other >>>> +architectures as well. >> >> No. RISC-V does not have the same requirements as ARM. E.g. the initrd >> can be located anywhere in memory. > > Please point to documentation that confirms that, and some otherwise bad > examples that actually work. [PATCH 1/1] RISC-V: load initrd wherever it fits into memory https://lore.kernel.org/all/20210629134018.62859-1-xypron.glpk@gmx.de/ Please, have a look at efi_get_max_initrd_addr() in these files: arch/arm/include/asm/efi.h:73 arch/arm64/include/asm/efi.h:77 arch/loongarch/include/asm/efi.h:36 arch/riscv/include/asm/efi.h:31 MAX_UNCOMP_KERNEL_SIZE = 32 MiB is only enforced in drivers/firmware/efi/libstub/arm32-stub.c. > >>>> + >>>> +Example Image locations >>>> +^^^^^^^^^^^^^^^^^^^^^^^ >> >> You seem not to refer to a file 'Image'. >> >> %s/Image/image/ > > OK. > >>>> + >>>> +If we take the Texas Instruments OMAP2PLUS family of ARMv7 processors as an >>>> +example for the above listed variables, we would do:: >> >> %s/we would do/we chose/ ? > > Either? I don't see it mattering either way. > >>>> + >>>> + loadaddr=0x82000000 >>>> + kernel_addr_r=${loadaddr} >>>> + fdt_addr_r=0x88000000 >>>> + ramdisk_addr_r=0x88080000 >>>> + bootm_size=0x10000000 >>>> + >>>> +To explain this, we start by noting that DRAM starts at 0x80000000. A 32MiB >>> >>> Should it say 'We use a 32MiB' ? >> >> Please, mention that MAX_UNCOMP_KERNEL_SIZE = 32 MiB is ARMv7 specific. > > Sorry? As I understood it last, the maximum size was something like > 96MiB before you have to employ some funky tricks. Look at the use of MAX_UNCOMP_KERNEL_SIZE in handle_kernel_image() of the EFI stub (drivers/firmware/efi/libstub/arm32-stub.c). > >>>> +buffer from the start of memory as our default load address, and so where the >>>> +kernel would also be loaded to. This will hopefully allow for us to have the >> >> %s/allow for us/allow/ >> >>>> +whole of the compressed kernel image exist in memory above where the whole of >>>> +the decompressed kernel image will be, and allow for a quicker boot. Next, we > > We use 32MiB for the reason I said here. Which is only a slight > rewording of the arm32 Linux booting document, and the section starts > out by saying this is an example for ARMv7 platforms. You ask all other architectures to follow this example? > >> Please, mention that decompressor code otherwise will have to relocate >> the compressed kernel. > > I'm not sure. Perhaps it would be good to also link to some of the > articles expanding upon how Linux on ARM32 boots, as part of more > general documentation, rather than a specific example here. Just look at the comment above the definition of MAX_UNCOMP_KERNEL_SIZE in arch/arm/include/asm/efi.h. > >>>> +say that the device tree will be placed at 128MiB offset from the start of >> >> Please, mention that initrd must be >> >> * within 512 MiB (0x20000000) of the memory start on arm >> (which restricts initrd_high) >> * in a a 1 GB aligned region of size '1UL << (VA_BITS_MIN - 1)' that >> includes the kernel on arm64 > > No, because this is not intended to list every constraint on ARM32 (nor > arm64, which would benefit from an example that's not TI, as TI arm64 > platforms share the same base address for memory). You ask above to follow the example of ARMv7 on all architectures. Hence it is necessary to point out the differences. Best regards Heinrich > >> On RISC-V such a limitation does not exist. > > I do wish that RISC-V had a similar document to ARM/ARM64, in Linux. > >>>> +memory. This is suggested by the kernel documment as it is exceedingly >> >> %s/documment/document >> >>>> +unlikely to be overwritten by the kernel itself given other architectural >>>> +constraints. We then allow for the device tree to be up to 512KiB in size >>>> +before placing the ramdisk in memory. We then say that everything should be >>>> +within the first 256MiB of memory so that U-Boot can relocate things as needed >>>> +to ensure proper alignment. We pick 256MiB as our value here because we know >> >> If the load address ranges occupy the first 256 MiB, where will be the >> space for relocation on a 256 MiB board? Without mentioning initrd_high >> this paragraph is incomplete. > > You don't need initrd_high / fdt_high when bootm_size is used. Maybe > that needs to be clearer in this paragraph and also the rest of the > documentation. > >>>> +there are very few platforms on in this family with less memory. It could be >>>> +as high as 768MiB and still ensure that everything would be visible to the >>>> +kernel, but again we go with what we assume is the safest assumption. >> >> A section per architecture clearly naming the architecture specific >> restrictions of Linux would be much more helpful. > > I did ask for further explained examples as it would indeed be good to > have at least one per architecture. >
On Mon, Jul 11, 2022 at 08:42:08AM +0200, Heinrich Schuchardt wrote: > On 7/10/22 18:17, Tom Rini wrote: > > On Sun, Jul 10, 2022 at 02:26:04PM +0200, Heinrich Schuchardt wrote: > > > On 6/30/22 12:06, Simon Glass wrote: > > > > On Mon, 20 Jun 2022 at 08:32, Tom Rini <trini@konsulko.com> wrote: > > > > > > > > > > Start by elaborating on what some of our constraints tend to be with > > > > > image location values, and document where these external constraints > > > > > come from. Provide a new subsection, an example based on the TI ARMv7 > > > > > OMAP2PLUS families of chips, that gives sample values and explains why > > > > > we use these particular values. This is based on what is in > > > > > include/configs/ti_armv7_common.h as of fb3ad9bd923d ("TI: Add, use a > > > > > DEFAULT_LINUX_BOOT_ENV environment string") as this contains just the > > > > > values referenced in this document now and not some of the further > > > > > additions that are less generic. > > > > > > > > > > Signed-off-by: Tom Rini <trini@konsulko.com> > > > > > --- > > > > > doc/usage/environment.rst | 39 +++++++++++++++++++++++++++++++++++++++ > > > > > 1 file changed, 39 insertions(+) > > > > > > > > Reviewed-by: Simon Glass <sjg@chromium.org> > > > > > > Below you want a change? > > > > Yes, often Simon does that (and it's fine) to both offer a tag but if > > another iteration is needed to make a minor adjustment to some wording > > or another, or to make when applying. Which is fine with me. > > > > > > > diff --git a/doc/usage/environment.rst b/doc/usage/environment.rst > > > > > index a9a4702632d2..f70ccd6a58ee 100644 > > > > > --- a/doc/usage/environment.rst > > > > > +++ b/doc/usage/environment.rst > > > > > @@ -404,6 +404,42 @@ device tree blob fdtfile fdt_addr_r fdt_addr > > > > > ramdisk ramdiskfile ramdisk_addr_r ramdisk_addr > > > > > ================= ============== ================ ============== > > > > > > > > > > +When setting the RAM addresses for `kernel_addr_r`, `fdt_addr_r` and > > > > > +`ramdisk_addr_r` there are several constraints to keep in mind. When booting > > > > > +Linux, the `Booting ARM Linux`_ and `Booting AArch64 Linux`_ documents lay out > > > > > +the requirements for booting all ARM platforms, including both alignment and > > > > > +where within memory various things must be. These guidelines tend to also be > > > > > +correct for other OSes and unless specifically contradicted by documentation > > > > > > What makes you think that BSD or Haiku have the same constraints as Linux? > > > > Because of what I said, and experience? Now, one may be a subset of > > another, but that still means it will work for both. This is intended > > to be general best practices. If you follow this then it's likely > > anything else will work too. The danger comes from trying to optimize > > the sizes to be as small as possible, rather than as large/flexible as > > will likely work anywhere. I will try and expand on that idea in the > > next iteration. > > > > > > > +specific to another architecture, are good rules to follow for other > > > > > +architectures as well. > > > > > > No. RISC-V does not have the same requirements as ARM. E.g. the initrd > > > can be located anywhere in memory. > > > > Please point to documentation that confirms that, and some otherwise bad > > examples that actually work. > > [PATCH 1/1] RISC-V: load initrd wherever it fits into memory > https://lore.kernel.org/all/20210629134018.62859-1-xypron.glpk@gmx.de/ Looks like someone ran in to the first common case of "oops, overwrote the ramdisk with the kernel bss" or something along those lines. Which is why I'm asking for more architectures to add good examples of where to load each payload in to memory, with explanations of why and how big of a gap to have. I _think_ in Linux RISC-V (and hopefully for 32bit and 64bit) used the arm64 Image format and so BSS size is available in the header and so we can safely check for that overlap and relocate rather than fail to boot. Checking for, and avoiding to start with, these types of problems is why I want to add the examples. > Please, have a look at efi_get_max_initrd_addr() in these files: > > arch/arm/include/asm/efi.h:73 > arch/arm64/include/asm/efi.h:77 > arch/loongarch/include/asm/efi.h:36 > arch/riscv/include/asm/efi.h:31 > > MAX_UNCOMP_KERNEL_SIZE = 32 MiB is only enforced in > drivers/firmware/efi/libstub/arm32-stub.c. This isn't an EFI thing however. The max uncompressed Linux kernel image for arm32 is something along the lines of 96MiB I recall rmk telling me when I asked about it at the time. The base+32MiB in the example here is for optimal (but not REQUIRED) decompressor location. > > > > > +Example Image locations > > > > > +^^^^^^^^^^^^^^^^^^^^^^^ > > > > > > You seem not to refer to a file 'Image'. > > > > > > %s/Image/image/ > > > > OK. > > > > > > > + > > > > > +If we take the Texas Instruments OMAP2PLUS family of ARMv7 processors as an > > > > > +example for the above listed variables, we would do:: > > > > > > %s/we would do/we chose/ ? > > > > Either? I don't see it mattering either way. > > > > > > > + > > > > > + loadaddr=0x82000000 > > > > > + kernel_addr_r=${loadaddr} > > > > > + fdt_addr_r=0x88000000 > > > > > + ramdisk_addr_r=0x88080000 > > > > > + bootm_size=0x10000000 > > > > > + > > > > > +To explain this, we start by noting that DRAM starts at 0x80000000. A 32MiB > > > > > > > > Should it say 'We use a 32MiB' ? > > > > > > Please, mention that MAX_UNCOMP_KERNEL_SIZE = 32 MiB is ARMv7 specific. > > > > Sorry? As I understood it last, the maximum size was something like > > 96MiB before you have to employ some funky tricks. > > Look at the use of MAX_UNCOMP_KERNEL_SIZE in handle_kernel_image() of > the EFI stub (drivers/firmware/efi/libstub/arm32-stub.c). > > > > > > > > +buffer from the start of memory as our default load address, and so where the > > > > > +kernel would also be loaded to. This will hopefully allow for us to have the > > > > > > %s/allow for us/allow/ > > > > > > > > +whole of the compressed kernel image exist in memory above where the whole of > > > > > +the decompressed kernel image will be, and allow for a quicker boot. Next, we > > > > We use 32MiB for the reason I said here. Which is only a slight > > rewording of the arm32 Linux booting document, and the section starts > > out by saying this is an example for ARMv7 platforms. > > You ask all other architectures to follow this example? I could have sworn that somewhere within the comments of this series I asked for more examples to be added, yes. And I know I intended to (since we _need_ them, and I think I've expressed me desire to have them before) and I am asking now. > > > Please, mention that decompressor code otherwise will have to relocate > > > the compressed kernel. > > > > I'm not sure. Perhaps it would be good to also link to some of the > > articles expanding upon how Linux on ARM32 boots, as part of more > > general documentation, rather than a specific example here. > > Just look at the comment above the definition of MAX_UNCOMP_KERNEL_SIZE > in arch/arm/include/asm/efi.h. Keep in mind this is only vaguely EFI-related. Given how long ago edkII for beagleboard was done, it doesn't quite predate EFI on ARM, but this example has been in long use for the common non-EFI case on 32bit ARM. > > > > > +say that the device tree will be placed at 128MiB offset from the start of > > > > > > Please, mention that initrd must be > > > > > > * within 512 MiB (0x20000000) of the memory start on arm > > > (which restricts initrd_high) > > > * in a a 1 GB aligned region of size '1UL << (VA_BITS_MIN - 1)' that > > > includes the kernel on arm64 > > > > No, because this is not intended to list every constraint on ARM32 (nor > > arm64, which would benefit from an example that's not TI, as TI arm64 > > platforms share the same base address for memory). > > You ask above to follow the example of ARMv7 on all architectures. Hence > it is necessary to point out the differences. No, I'm asking for more examples to be added for each architecture.
On 7/11/22 14:41, Tom Rini wrote: > On Mon, Jul 11, 2022 at 08:42:08AM +0200, Heinrich Schuchardt wrote: >> On 7/10/22 18:17, Tom Rini wrote: >>> On Sun, Jul 10, 2022 at 02:26:04PM +0200, Heinrich Schuchardt wrote: >>>> On 6/30/22 12:06, Simon Glass wrote: >>>>> On Mon, 20 Jun 2022 at 08:32, Tom Rini <trini@konsulko.com> wrote: >>>>>> >>>>>> Start by elaborating on what some of our constraints tend to be with >>>>>> image location values, and document where these external constraints >>>>>> come from. Provide a new subsection, an example based on the TI ARMv7 >>>>>> OMAP2PLUS families of chips, that gives sample values and explains why >>>>>> we use these particular values. This is based on what is in >>>>>> include/configs/ti_armv7_common.h as of fb3ad9bd923d ("TI: Add, use a >>>>>> DEFAULT_LINUX_BOOT_ENV environment string") as this contains just the >>>>>> values referenced in this document now and not some of the further >>>>>> additions that are less generic. >>>>>> >>>>>> Signed-off-by: Tom Rini <trini@konsulko.com> >>>>>> --- >>>>>> doc/usage/environment.rst | 39 +++++++++++++++++++++++++++++++++++++++ >>>>>> 1 file changed, 39 insertions(+) >>>>> >>>>> Reviewed-by: Simon Glass <sjg@chromium.org> >>>> >>>> Below you want a change? >>> >>> Yes, often Simon does that (and it's fine) to both offer a tag but if >>> another iteration is needed to make a minor adjustment to some wording >>> or another, or to make when applying. Which is fine with me. >>> >>>>>> diff --git a/doc/usage/environment.rst b/doc/usage/environment.rst >>>>>> index a9a4702632d2..f70ccd6a58ee 100644 >>>>>> --- a/doc/usage/environment.rst >>>>>> +++ b/doc/usage/environment.rst >>>>>> @@ -404,6 +404,42 @@ device tree blob fdtfile fdt_addr_r fdt_addr >>>>>> ramdisk ramdiskfile ramdisk_addr_r ramdisk_addr >>>>>> ================= ============== ================ ============== >>>>>> >>>>>> +When setting the RAM addresses for `kernel_addr_r`, `fdt_addr_r` and >>>>>> +`ramdisk_addr_r` there are several constraints to keep in mind. When booting >>>>>> +Linux, the `Booting ARM Linux`_ and `Booting AArch64 Linux`_ documents lay out >>>>>> +the requirements for booting all ARM platforms, including both alignment and >>>>>> +where within memory various things must be. These guidelines tend to also be >>>>>> +correct for other OSes and unless specifically contradicted by documentation >>>> >>>> What makes you think that BSD or Haiku have the same constraints as Linux? >>> >>> Because of what I said, and experience? Now, one may be a subset of >>> another, but that still means it will work for both. This is intended >>> to be general best practices. If you follow this then it's likely >>> anything else will work too. The danger comes from trying to optimize >>> the sizes to be as small as possible, rather than as large/flexible as >>> will likely work anywhere. I will try and expand on that idea in the >>> next iteration. >>> >>>>>> +specific to another architecture, are good rules to follow for other >>>>>> +architectures as well. >>>> >>>> No. RISC-V does not have the same requirements as ARM. E.g. the initrd >>>> can be located anywhere in memory. >>> >>> Please point to documentation that confirms that, and some otherwise bad >>> examples that actually work. >> >> [PATCH 1/1] RISC-V: load initrd wherever it fits into memory >> https://lore.kernel.org/all/20210629134018.62859-1-xypron.glpk@gmx.de/ > > Looks like someone ran in to the first common case of "oops, overwrote > the ramdisk with the kernel bss" or something along those lines. Not at all. The ramdisk was relocated by U-Boot unnecessarily to above 256 MiB after start of RAM and the EFI stub before the patch did not accept this address for no reason. > > Which is why I'm asking for more architectures to add good examples of > where to load each payload in to memory, with explanations of why and > how big of a gap to have. I _think_ in Linux RISC-V (and hopefully for > 32bit and 64bit) used the arm64 Image format and so BSS size is > available in the header and so we can safely check for that overlap and > relocate rather than fail to boot. Checking for, and avoiding to start > with, these types of problems is why I want to add the examples. I am not aware of any restrictions for the placement of kernel, initrd, fdt for RISC-V. Therefore there is no need to relocate anything after loading (without overlap). The bootefi command will never relocate a kernel or an fdt on any architecture. You just pass the original load addresses. > >> Please, have a look at efi_get_max_initrd_addr() in these files: >> >> arch/arm/include/asm/efi.h:73 >> arch/arm64/include/asm/efi.h:77 >> arch/loongarch/include/asm/efi.h:36 >> arch/riscv/include/asm/efi.h:31 >> >> MAX_UNCOMP_KERNEL_SIZE = 32 MiB is only enforced in >> drivers/firmware/efi/libstub/arm32-stub.c. > > This isn't an EFI thing however. The max uncompressed Linux kernel > image for arm32 is something along the lines of 96MiB I recall rmk > telling me when I asked about it at the time. The base+32MiB in the > example here is for optimal (but not REQUIRED) decompressor location. The decompressor is what follows the EFI stub in the image? > >>>>>> +Example Image locations >>>>>> +^^^^^^^^^^^^^^^^^^^^^^^ >>>> >>>> You seem not to refer to a file 'Image'. >>>> >>>> %s/Image/image/ >>> >>> OK. >>> >>>>>> + >>>>>> +If we take the Texas Instruments OMAP2PLUS family of ARMv7 processors as an >>>>>> +example for the above listed variables, we would do:: >>>> >>>> %s/we would do/we chose/ ? >>> >>> Either? I don't see it mattering either way. >>> >>>>>> + >>>>>> + loadaddr=0x82000000 >>>>>> + kernel_addr_r=${loadaddr} >>>>>> + fdt_addr_r=0x88000000 >>>>>> + ramdisk_addr_r=0x88080000 >>>>>> + bootm_size=0x10000000 >>>>>> + >>>>>> +To explain this, we start by noting that DRAM starts at 0x80000000. A 32MiB >>>>> >>>>> Should it say 'We use a 32MiB' ? >>>> >>>> Please, mention that MAX_UNCOMP_KERNEL_SIZE = 32 MiB is ARMv7 specific. >>> >>> Sorry? As I understood it last, the maximum size was something like >>> 96MiB before you have to employ some funky tricks. >> >> Look at the use of MAX_UNCOMP_KERNEL_SIZE in handle_kernel_image() of >> the EFI stub (drivers/firmware/efi/libstub/arm32-stub.c). >> >>> >>>>>> +buffer from the start of memory as our default load address, and so where the >>>>>> +kernel would also be loaded to. This will hopefully allow for us to have the >>>> >>>> %s/allow for us/allow/ >>>> >>>>>> +whole of the compressed kernel image exist in memory above where the whole of >>>>>> +the decompressed kernel image will be, and allow for a quicker boot. Next, we >>> >>> We use 32MiB for the reason I said here. Which is only a slight >>> rewording of the arm32 Linux booting document, and the section starts >>> out by saying this is an example for ARMv7 platforms. >> >> You ask all other architectures to follow this example? > > I could have sworn that somewhere within the comments of this series I > asked for more examples to be added, yes. And I know I intended to > (since we _need_ them, and I think I've expressed me desire to have them > before) and I am asking now. > >>>> Please, mention that decompressor code otherwise will have to relocate >>>> the compressed kernel. >>> >>> I'm not sure. Perhaps it would be good to also link to some of the >>> articles expanding upon how Linux on ARM32 boots, as part of more >>> general documentation, rather than a specific example here. >> >> Just look at the comment above the definition of MAX_UNCOMP_KERNEL_SIZE >> in arch/arm/include/asm/efi.h. > > Keep in mind this is only vaguely EFI-related. Given how long ago edkII > for beagleboard was done, it doesn't quite predate EFI on ARM, but this > example has been in long use for the common non-EFI case on 32bit ARM. The EFI stub is using the value due to (assumed) restrictions in the decompressor and main kernel. Best regards Heinrich > >>>>>> +say that the device tree will be placed at 128MiB offset from the start of >>>> >>>> Please, mention that initrd must be >>>> >>>> * within 512 MiB (0x20000000) of the memory start on arm >>>> (which restricts initrd_high) >>>> * in a a 1 GB aligned region of size '1UL << (VA_BITS_MIN - 1)' that >>>> includes the kernel on arm64 >>> >>> No, because this is not intended to list every constraint on ARM32 (nor >>> arm64, which would benefit from an example that's not TI, as TI arm64 >>> platforms share the same base address for memory). >> >> You ask above to follow the example of ARMv7 on all architectures. Hence >> it is necessary to point out the differences. > > No, I'm asking for more examples to be added for each architecture. >
On Mon, Jul 11, 2022 at 03:10:36PM +0200, Heinrich Schuchardt wrote: > On 7/11/22 14:41, Tom Rini wrote: > > On Mon, Jul 11, 2022 at 08:42:08AM +0200, Heinrich Schuchardt wrote: > > > On 7/10/22 18:17, Tom Rini wrote: > > > > On Sun, Jul 10, 2022 at 02:26:04PM +0200, Heinrich Schuchardt wrote: > > > > > On 6/30/22 12:06, Simon Glass wrote: > > > > > > On Mon, 20 Jun 2022 at 08:32, Tom Rini <trini@konsulko.com> wrote: > > > > > > > > > > > > > > Start by elaborating on what some of our constraints tend to be with > > > > > > > image location values, and document where these external constraints > > > > > > > come from. Provide a new subsection, an example based on the TI ARMv7 > > > > > > > OMAP2PLUS families of chips, that gives sample values and explains why > > > > > > > we use these particular values. This is based on what is in > > > > > > > include/configs/ti_armv7_common.h as of fb3ad9bd923d ("TI: Add, use a > > > > > > > DEFAULT_LINUX_BOOT_ENV environment string") as this contains just the > > > > > > > values referenced in this document now and not some of the further > > > > > > > additions that are less generic. > > > > > > > > > > > > > > Signed-off-by: Tom Rini <trini@konsulko.com> > > > > > > > --- > > > > > > > doc/usage/environment.rst | 39 +++++++++++++++++++++++++++++++++++++++ > > > > > > > 1 file changed, 39 insertions(+) > > > > > > > > > > > > Reviewed-by: Simon Glass <sjg@chromium.org> > > > > > > > > > > Below you want a change? > > > > > > > > Yes, often Simon does that (and it's fine) to both offer a tag but if > > > > another iteration is needed to make a minor adjustment to some wording > > > > or another, or to make when applying. Which is fine with me. > > > > > > > > > > > diff --git a/doc/usage/environment.rst b/doc/usage/environment.rst > > > > > > > index a9a4702632d2..f70ccd6a58ee 100644 > > > > > > > --- a/doc/usage/environment.rst > > > > > > > +++ b/doc/usage/environment.rst > > > > > > > @@ -404,6 +404,42 @@ device tree blob fdtfile fdt_addr_r fdt_addr > > > > > > > ramdisk ramdiskfile ramdisk_addr_r ramdisk_addr > > > > > > > ================= ============== ================ ============== > > > > > > > > > > > > > > +When setting the RAM addresses for `kernel_addr_r`, `fdt_addr_r` and > > > > > > > +`ramdisk_addr_r` there are several constraints to keep in mind. When booting > > > > > > > +Linux, the `Booting ARM Linux`_ and `Booting AArch64 Linux`_ documents lay out > > > > > > > +the requirements for booting all ARM platforms, including both alignment and > > > > > > > +where within memory various things must be. These guidelines tend to also be > > > > > > > +correct for other OSes and unless specifically contradicted by documentation > > > > > > > > > > What makes you think that BSD or Haiku have the same constraints as Linux? > > > > > > > > Because of what I said, and experience? Now, one may be a subset of > > > > another, but that still means it will work for both. This is intended > > > > to be general best practices. If you follow this then it's likely > > > > anything else will work too. The danger comes from trying to optimize > > > > the sizes to be as small as possible, rather than as large/flexible as > > > > will likely work anywhere. I will try and expand on that idea in the > > > > next iteration. > > > > > > > > > > > +specific to another architecture, are good rules to follow for other > > > > > > > +architectures as well. > > > > > > > > > > No. RISC-V does not have the same requirements as ARM. E.g. the initrd > > > > > can be located anywhere in memory. > > > > > > > > Please point to documentation that confirms that, and some otherwise bad > > > > examples that actually work. > > > > > > [PATCH 1/1] RISC-V: load initrd wherever it fits into memory > > > https://lore.kernel.org/all/20210629134018.62859-1-xypron.glpk@gmx.de/ > > > > Looks like someone ran in to the first common case of "oops, overwrote > > the ramdisk with the kernel bss" or something along those lines. > > Not at all. The ramdisk was relocated by U-Boot unnecessarily to above > 256 MiB after start of RAM and the EFI stub before the patch did not > accept this address for no reason. Then bootm_size / bootm_low should have been set appropriately in U-Boot. > > Which is why I'm asking for more architectures to add good examples of > > where to load each payload in to memory, with explanations of why and > > how big of a gap to have. I _think_ in Linux RISC-V (and hopefully for > > 32bit and 64bit) used the arm64 Image format and so BSS size is > > available in the header and so we can safely check for that overlap and > > relocate rather than fail to boot. Checking for, and avoiding to start > > with, these types of problems is why I want to add the examples. > > I am not aware of any restrictions for the placement of kernel, initrd, > fdt for RISC-V. Therefore there is no need to relocate anything after > loading (without overlap). > > The bootefi command will never relocate a kernel or an fdt on any > architecture. You just pass the original load addresses. Which is all the more reason we need to ensure that the fdt and initrd are placed in appropriately aligned and non-overlapping locations. Because if you put the initrd too close to where the kernel ends up, the BSS will eat your ramdisk before it can go "oh, there's a ramdisk there". That's a practical, not architectural, problem. Same with the device tree. > > > Please, have a look at efi_get_max_initrd_addr() in these files: > > > > > > arch/arm/include/asm/efi.h:73 > > > arch/arm64/include/asm/efi.h:77 > > > arch/loongarch/include/asm/efi.h:36 > > > arch/riscv/include/asm/efi.h:31 > > > > > > MAX_UNCOMP_KERNEL_SIZE = 32 MiB is only enforced in > > > drivers/firmware/efi/libstub/arm32-stub.c. > > > > This isn't an EFI thing however. The max uncompressed Linux kernel > > image for arm32 is something along the lines of 96MiB I recall rmk > > telling me when I asked about it at the time. The base+32MiB in the > > example here is for optimal (but not REQUIRED) decompressor location. > > The decompressor is what follows the EFI stub in the image? I'm not talking about EFI at all in this example, as it's 32bit ARM, not 64bit ARM or RISC-V. > > > > > > > +Example Image locations > > > > > > > +^^^^^^^^^^^^^^^^^^^^^^^ > > > > > > > > > > You seem not to refer to a file 'Image'. > > > > > > > > > > %s/Image/image/ > > > > > > > > OK. > > > > > > > > > > > + > > > > > > > +If we take the Texas Instruments OMAP2PLUS family of ARMv7 processors as an > > > > > > > +example for the above listed variables, we would do:: > > > > > > > > > > %s/we would do/we chose/ ? > > > > > > > > Either? I don't see it mattering either way. > > > > > > > > > > > + > > > > > > > + loadaddr=0x82000000 > > > > > > > + kernel_addr_r=${loadaddr} > > > > > > > + fdt_addr_r=0x88000000 > > > > > > > + ramdisk_addr_r=0x88080000 > > > > > > > + bootm_size=0x10000000 > > > > > > > + > > > > > > > +To explain this, we start by noting that DRAM starts at 0x80000000. A 32MiB > > > > > > > > > > > > Should it say 'We use a 32MiB' ? > > > > > > > > > > Please, mention that MAX_UNCOMP_KERNEL_SIZE = 32 MiB is ARMv7 specific. > > > > > > > > Sorry? As I understood it last, the maximum size was something like > > > > 96MiB before you have to employ some funky tricks. > > > > > > Look at the use of MAX_UNCOMP_KERNEL_SIZE in handle_kernel_image() of > > > the EFI stub (drivers/firmware/efi/libstub/arm32-stub.c). > > > > > > > > > > > > > > +buffer from the start of memory as our default load address, and so where the > > > > > > > +kernel would also be loaded to. This will hopefully allow for us to have the > > > > > > > > > > %s/allow for us/allow/ > > > > > > > > > > > > +whole of the compressed kernel image exist in memory above where the whole of > > > > > > > +the decompressed kernel image will be, and allow for a quicker boot. Next, we > > > > > > > > We use 32MiB for the reason I said here. Which is only a slight > > > > rewording of the arm32 Linux booting document, and the section starts > > > > out by saying this is an example for ARMv7 platforms. > > > > > > You ask all other architectures to follow this example? > > > > I could have sworn that somewhere within the comments of this series I > > asked for more examples to be added, yes. And I know I intended to > > (since we _need_ them, and I think I've expressed me desire to have them > > before) and I am asking now. > > > > > > > Please, mention that decompressor code otherwise will have to relocate > > > > > the compressed kernel. > > > > > > > > I'm not sure. Perhaps it would be good to also link to some of the > > > > articles expanding upon how Linux on ARM32 boots, as part of more > > > > general documentation, rather than a specific example here. > > > > > > Just look at the comment above the definition of MAX_UNCOMP_KERNEL_SIZE > > > in arch/arm/include/asm/efi.h. > > > > Keep in mind this is only vaguely EFI-related. Given how long ago edkII > > for beagleboard was done, it doesn't quite predate EFI on ARM, but this > > example has been in long use for the common non-EFI case on 32bit ARM. > > The EFI stub is using the value due to (assumed) restrictions in the > decompressor and main kernel. OK, but EFI is largely irrelevant to the 32bit ARM case, which is what this example is for.
diff --git a/doc/usage/environment.rst b/doc/usage/environment.rst index a9a4702632d2..f70ccd6a58ee 100644 --- a/doc/usage/environment.rst +++ b/doc/usage/environment.rst @@ -404,6 +404,42 @@ device tree blob fdtfile fdt_addr_r fdt_addr ramdisk ramdiskfile ramdisk_addr_r ramdisk_addr ================= ============== ================ ============== +When setting the RAM addresses for `kernel_addr_r`, `fdt_addr_r` and +`ramdisk_addr_r` there are several constraints to keep in mind. When booting +Linux, the `Booting ARM Linux`_ and `Booting AArch64 Linux`_ documents lay out +the requirements for booting all ARM platforms, including both alignment and +where within memory various things must be. These guidelines tend to also be +correct for other OSes and unless specifically contradicted by documentation +specific to another architecture, are good rules to follow for other +architectures as well. + +Example Image locations +^^^^^^^^^^^^^^^^^^^^^^^ + +If we take the Texas Instruments OMAP2PLUS family of ARMv7 processors as an +example for the above listed variables, we would do:: + + loadaddr=0x82000000 + kernel_addr_r=${loadaddr} + fdt_addr_r=0x88000000 + ramdisk_addr_r=0x88080000 + bootm_size=0x10000000 + +To explain this, we start by noting that DRAM starts at 0x80000000. A 32MiB +buffer from the start of memory as our default load address, and so where the +kernel would also be loaded to. This will hopefully allow for us to have the +whole of the compressed kernel image exist in memory above where the whole of +the decompressed kernel image will be, and allow for a quicker boot. Next, we +say that the device tree will be placed at 128MiB offset from the start of +memory. This is suggested by the kernel documment as it is exceedingly +unlikely to be overwritten by the kernel itself given other architectural +constraints. We then allow for the device tree to be up to 512KiB in size +before placing the ramdisk in memory. We then say that everything should be +within the first 256MiB of memory so that U-Boot can relocate things as needed +to ensure proper alignment. We pick 256MiB as our value here because we know +there are very few platforms on in this family with less memory. It could be +as high as 768MiB and still ensure that everything would be visible to the +kernel, but again we go with what we assume is the safest assumption. Automatically updated variables ------------------------------- @@ -472,3 +508,6 @@ Implementation -------------- See :doc:`../develop/environment` for internal development details. + +.. _`Booting ARM Linux`: https://www.kernel.org/doc/html/latest/arm/booting.html +.. _`Booting AArch64 Linux`: https://www.kernel.org/doc/html/latest/arm64/booting.html
Start by elaborating on what some of our constraints tend to be with image location values, and document where these external constraints come from. Provide a new subsection, an example based on the TI ARMv7 OMAP2PLUS families of chips, that gives sample values and explains why we use these particular values. This is based on what is in include/configs/ti_armv7_common.h as of fb3ad9bd923d ("TI: Add, use a DEFAULT_LINUX_BOOT_ENV environment string") as this contains just the values referenced in this document now and not some of the further additions that are less generic. Signed-off-by: Tom Rini <trini@konsulko.com> --- doc/usage/environment.rst | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+)