| Message ID | 20210725164400.468319-3-sjg@chromium.org |
|---|---|
| State | Changes Requested |
| Delegated to: | Heinrich Schuchardt |
| Headers | show |
| Series | [1/3] doc: Move devicetree control doc to rST | expand |
On 7/25/21 6:44 PM, 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> > --- > > doc/develop/devicetree/control.rst | 2 ++ > doc/develop/devicetree/intro.rst | 39 ++++++++++++++++++++++++++++++ > 2 files changed, 41 insertions(+) > > diff --git a/doc/develop/devicetree/control.rst b/doc/develop/devicetree/control.rst > index ac5f7989cc6..f98faee20d1 100644 > --- a/doc/develop/devicetree/control.rst > +++ b/doc/develop/devicetree/control.rst > @@ -174,6 +174,8 @@ 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..e03d8e1ae66 100644 > --- a/doc/develop/devicetree/intro.rst > +++ b/doc/develop/devicetree/intro.rst > @@ -2,3 +2,42 @@ > > Devicetree Introduction > ======================= > + > +U-Boot uses devicetree for configuration. This includes the devices used by %s/devicetree/devicetrees/ or 'uses a' > +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 in the %s/in/into/ ? > +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 / runtime info go in the devicetree in U-Boot. Do you mean 'configuration and runtime' or 'runtime configuration'? %s/info go in/information goes into/ > + > +Of course it is possible to: > + > +- add tables into the rodata %s/rodata/rodata section of the U-Boot binary/ > +- append some info to the end of U-Boot in a different format > +- modify the link script to bring in a file with some info in it %s/link/linker/ > +- put things in ACPI tables %s/in/into/ ? > +- compile in a UEFI hand-off block structure and put things in there %s/compile/link/ ? > + > +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 %s/So please.../So, please, / Best regards Heinrich > +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 ac5f7989cc6..f98faee20d1 100644 --- a/doc/develop/devicetree/control.rst +++ b/doc/develop/devicetree/control.rst @@ -174,6 +174,8 @@ 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..e03d8e1ae66 100644 --- a/doc/develop/devicetree/intro.rst +++ b/doc/develop/devicetree/intro.rst @@ -2,3 +2,42 @@ Devicetree Introduction ======================= + +U-Boot uses 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 in 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 / runtime info go in the devicetree in U-Boot. + +Of course it is possible to: + +- add tables into the rodata +- append some info to the end of U-Boot in a different format +- modify the link script to bring in a file with some info in it +- put things in ACPI tables +- compile 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> --- doc/develop/devicetree/control.rst | 2 ++ doc/develop/devicetree/intro.rst | 39 ++++++++++++++++++++++++++++++ 2 files changed, 41 insertions(+)