| Message ID | 20210802005713.2268145-3-sjg@chromium.org |
|---|---|
| State | Accepted, archived |
| Commit | 6a055c0f91418b78949b901147a63f2a4e26c9ab |
| Delegated to: | Heinrich Schuchardt |
| Headers | show |
| Series | [v2,1/3] doc: Move devicetree control doc to rST | expand |
On 8/2/21 2:57 AM, Simon Glass wrote: > This question comes up every now and then with people coming from Linux. > Add some notes about it so we can point to it in the mailing list. > > Signed-off-by: Simon Glass <sjg@chromium.org> Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de> > --- > > Changes in v2: > - Updates based on suggestions from Heinrich > > doc/develop/devicetree/control.rst | 2 ++ > doc/develop/devicetree/intro.rst | 40 ++++++++++++++++++++++++++++++ > 2 files changed, 42 insertions(+) > > diff --git a/doc/develop/devicetree/control.rst b/doc/develop/devicetree/control.rst > index 9f2c21034d0..b33e2a7ead6 100644 > --- a/doc/develop/devicetree/control.rst > +++ b/doc/develop/devicetree/control.rst > @@ -152,6 +152,8 @@ ways: > $ make DEVICE_TREE=<dts-file-name> > > > +.. _dttweaks: > + > Adding tweaks for U-Boot > ------------------------ > > diff --git a/doc/develop/devicetree/intro.rst b/doc/develop/devicetree/intro.rst > index 344851327c7..36e8cc0d440 100644 > --- a/doc/develop/devicetree/intro.rst > +++ b/doc/develop/devicetree/intro.rst > @@ -2,3 +2,43 @@ > > Devicetree Introduction > ======================= > + > +U-Boot uses a devicetree for configuration. This includes the devices used by > +the board, the format of the image created with binman, which UART to use for > +the console, public keys used for secure boot and many other things. > + > +See :doc:`control` for more information. > + > +Why does U-Boot put <thing> in the devicetree? > +---------------------------------------------- > + > +This question comes up a lot with people new to U-Boot, particular those coming > +from Linux who are used to quite strict rules about what can go into the > +devicetree. > + > +U-Boot uses the same devicetree as Linux but adds more things necessary for the > +bootloader environment (see :ref:`dttweaks`). > + > +U-Boot does not have a user space to provide policy and configuration. It cannot > +do what Linux does and run programs and look up filesystems to figure out how to > +boot. So configuration and runtime information goes into the devicetree in > +U-Boot. > + > +Of course it is possible to: > + > +- add tables into the rodata section of the U-Boot binary > +- append some info to the end of U-Boot in a different format > +- modify the linker script to bring in a file with some info in it > +- put things in ACPI tables > +- link in a UEFI hand-off block structure and put things in there > + > +but *please don't*. In general, devicetree is the sane place to hold U-Boot's > +configuration. > + > +So, please, do NOT ask why U-Boot puts <thing> in the devicetree. It is the only > +place it can go. It is a highly suitable data structure for just about anything > +that U-Boot needs to know at runtime. > + > +Note, it is possible to use platdata directly so drivers avoid devicetreee in > +SPL. But of-platdata is the modern way of avoiding devicetree overhead, so > +please use that instead. >
Heinrich, On Sat, Aug 14, 2021 at 09:21:25AM +0200, Heinrich Schuchardt wrote: > On 8/2/21 2:57 AM, Simon Glass wrote: > > This question comes up every now and then with people coming from Linux. > > Add some notes about it so we can point to it in the mailing list. > > > > Signed-off-by: Simon Glass <sjg@chromium.org> > > Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de> If I correctly understand here, Simon's intent is to reassure his opinion that a public key for capsule authentication should be stored in a device tree, not be embedded in U-Boot binary. So at the end, do you agree to reverting[1] Ilias' patch? -Takahiro Akashi [1] https://lists.denx.de/pipermail/u-boot/2021-August/456968.html > > --- > > > > Changes in v2: > > - Updates based on suggestions from Heinrich > > > > doc/develop/devicetree/control.rst | 2 ++ > > doc/develop/devicetree/intro.rst | 40 ++++++++++++++++++++++++++++++ > > 2 files changed, 42 insertions(+) > > > > diff --git a/doc/develop/devicetree/control.rst b/doc/develop/devicetree/control.rst > > index 9f2c21034d0..b33e2a7ead6 100644 > > --- a/doc/develop/devicetree/control.rst > > +++ b/doc/develop/devicetree/control.rst > > @@ -152,6 +152,8 @@ ways: > > $ make DEVICE_TREE=<dts-file-name> > > > > > > +.. _dttweaks: > > + > > Adding tweaks for U-Boot > > ------------------------ > > > > diff --git a/doc/develop/devicetree/intro.rst b/doc/develop/devicetree/intro.rst > > index 344851327c7..36e8cc0d440 100644 > > --- a/doc/develop/devicetree/intro.rst > > +++ b/doc/develop/devicetree/intro.rst > > @@ -2,3 +2,43 @@ > > > > Devicetree Introduction > > ======================= > > + > > +U-Boot uses a devicetree for configuration. This includes the devices used by > > +the board, the format of the image created with binman, which UART to use for > > +the console, public keys used for secure boot and many other things. > > + > > +See :doc:`control` for more information. > > + > > +Why does U-Boot put <thing> in the devicetree? > > +---------------------------------------------- > > + > > +This question comes up a lot with people new to U-Boot, particular those coming > > +from Linux who are used to quite strict rules about what can go into the > > +devicetree. > > + > > +U-Boot uses the same devicetree as Linux but adds more things necessary for the > > +bootloader environment (see :ref:`dttweaks`). > > + > > +U-Boot does not have a user space to provide policy and configuration. It cannot > > +do what Linux does and run programs and look up filesystems to figure out how to > > +boot. So configuration and runtime information goes into the devicetree in > > +U-Boot. > > + > > +Of course it is possible to: > > + > > +- add tables into the rodata section of the U-Boot binary > > +- append some info to the end of U-Boot in a different format > > +- modify the linker script to bring in a file with some info in it > > +- put things in ACPI tables > > +- link in a UEFI hand-off block structure and put things in there > > + > > +but *please don't*. In general, devicetree is the sane place to hold U-Boot's > > +configuration. > > + > > +So, please, do NOT ask why U-Boot puts <thing> in the devicetree. It is the only > > +place it can go. It is a highly suitable data structure for just about anything > > +that U-Boot needs to know at runtime. > > + > > +Note, it is possible to use platdata directly so drivers avoid devicetreee in > > +SPL. But of-platdata is the modern way of avoiding devicetree overhead, so > > +please use that instead. > > >
diff --git a/doc/develop/devicetree/control.rst b/doc/develop/devicetree/control.rst index 9f2c21034d0..b33e2a7ead6 100644 --- a/doc/develop/devicetree/control.rst +++ b/doc/develop/devicetree/control.rst @@ -152,6 +152,8 @@ ways: $ make DEVICE_TREE=<dts-file-name> +.. _dttweaks: + Adding tweaks for U-Boot ------------------------ diff --git a/doc/develop/devicetree/intro.rst b/doc/develop/devicetree/intro.rst index 344851327c7..36e8cc0d440 100644 --- a/doc/develop/devicetree/intro.rst +++ b/doc/develop/devicetree/intro.rst @@ -2,3 +2,43 @@ Devicetree Introduction ======================= + +U-Boot uses a devicetree for configuration. This includes the devices used by +the board, the format of the image created with binman, which UART to use for +the console, public keys used for secure boot and many other things. + +See :doc:`control` for more information. + +Why does U-Boot put <thing> in the devicetree? +---------------------------------------------- + +This question comes up a lot with people new to U-Boot, particular those coming +from Linux who are used to quite strict rules about what can go into the +devicetree. + +U-Boot uses the same devicetree as Linux but adds more things necessary for the +bootloader environment (see :ref:`dttweaks`). + +U-Boot does not have a user space to provide policy and configuration. It cannot +do what Linux does and run programs and look up filesystems to figure out how to +boot. So configuration and runtime information goes into the devicetree in +U-Boot. + +Of course it is possible to: + +- add tables into the rodata section of the U-Boot binary +- append some info to the end of U-Boot in a different format +- modify the linker script to bring in a file with some info in it +- put things in ACPI tables +- link in a UEFI hand-off block structure and put things in there + +but *please don't*. In general, devicetree is the sane place to hold U-Boot's +configuration. + +So, please, do NOT ask why U-Boot puts <thing> in the devicetree. It is the only +place it can go. It is a highly suitable data structure for just about anything +that U-Boot needs to know at runtime. + +Note, it is possible to use platdata directly so drivers avoid devicetreee in +SPL. But of-platdata is the modern way of avoiding devicetree overhead, so +please use that instead.
This question comes up every now and then with people coming from Linux. Add some notes about it so we can point to it in the mailing list. Signed-off-by: Simon Glass <sjg@chromium.org> --- Changes in v2: - Updates based on suggestions from Heinrich doc/develop/devicetree/control.rst | 2 ++ doc/develop/devicetree/intro.rst | 40 ++++++++++++++++++++++++++++++ 2 files changed, 42 insertions(+)