On Wed, Oct 13, 2021 at 10:15:02AM +0200, François Ozog wrote:
Le sam. 18 sept. 2021 à 15:18, Tom Rini trini@konsulko.com a écrit :
On Sat, Sep 18, 2021 at 03:38:45AM -0600, Simon Glass wrote:
Hi,
On Fri, 10 Sept 2021 at 16:44, Tom Rini trini@konsulko.com wrote:
On Sat, Sep 11, 2021 at 12:09:40AM +0200, Mark Kettenis wrote:
Date: Fri, 10 Sep 2021 17:17:37 -0400 From: Tom Rini trini@konsulko.com
On Fri, Sep 10, 2021 at 11:12:20PM +0200, Mark Kettenis wrote: > > Date: Fri, 10 Sep 2021 08:34:20 -0400 > > From: Tom Rini trini@konsulko.com > > > > On Fri, Sep 10, 2021 at 10:38:17AM +0200, Heinrich Schuchardt
wrote:
> > > > > > > > > On 9/9/21 10:10 PM, Simon Glass wrote: > > > > At present some of the ideas and techniques behind
devicetree in U-Boot
> > > > are assumed, implied or unsaid. Add some documentation to
cover how
> > > > devicetree is build, how it can be modified and the rules
about using
> > > > the various CONFIG_OF_... options. > > > > > > > > Signed-off-by: Simon Glass sjg@chromium.org > > > > Reviewed-by: Marcel Ziswiler marcel.ziswiler@toradex.com > > > > --- > > > > > > > > Changes in v3: > > > > - Fix typos linst suppled receive EFL > > > > - Drop 'and' before 'self-defeating' > > > > - Reword mention of control of QEMU's devicetree generation > > > > - Add mention of dropping CONFIG_OF_BOARD > > > > - Clarify the 'Once this bug is fixed' paragraph a bit > > > > - Expand ways that CONFIG_OF_PRIOR_STAGE can support the
U-Boot devicetree
> > > > - Add a note at the top explaining that his patch covers
'now', not 'future'
> > > > - Add note 'Note: Some boards use a devicetree in U-Boot
which does not match'
> > > > > > > > Changes in v2: > > > > - Fix typos per Sean (thank you!) and a few others > > > > - Add a 'Use of U-Boot /config node' section > > > > - Drop mention of dm-verity since that actually uses the
kernel cmdline
> > > > - Explain that OF_BOARD will still work after these
changes (in
> > > > 'Once this bug is fixed...' paragraph) > > > > - Expand a bit on the reason why the 'Current situation'
is bad
> > > > - Clarify in a second place that Linux and U-Boot use the
same devicetree
> > > > in 'To be clear, while U-Boot...' > > > > - Expand on why we should have rules for other projects in > > > > 'Devicetree in another project' > > > > - Add a comment as to why devicetree in U-Boot is not 'bad
design'
> > > > - Reword 'in-tree U-Boot devicetree' to 'devicetree source
in U-Boot'
> > > > - Rewrite 'Devicetree generated on-the-fly in another
project' to cover
> > > > points raised on v1 > > > > - Add 'Why does U-Boot have its nodes and properties?' > > > > - Add 'Why not have two devicetrees?' > > > > > > > > doc/develop/index.rst | 1 + > > > > doc/develop/package/devicetree.rst | 583
+++++++++++++++++++++++++++++
> > > > doc/develop/package/index.rst | 1 + > > > > 3 files changed, 585 insertions(+) > > > > create mode 100644 doc/develop/package/devicetree.rst > > > > > > > > diff --git a/doc/develop/index.rst b/doc/develop/index.rst > > > > index 83c929babda..d5ad8f9fe53 100644 > > > > --- a/doc/develop/index.rst > > > > +++ b/doc/develop/index.rst > > > > @@ -36,6 +36,7 @@ Packaging > > > > :maxdepth: 1 > > > > > > > > package/index > > > > + package/devicetree > > > > > > > > Testing > > > > ------- > > > > diff --git a/doc/develop/package/devicetree.rst
b/doc/develop/package/devicetree.rst
> > > > new file mode 100644 > > > > index 00000000000..b1bd310d906 > > > > --- /dev/null > > > > +++ b/doc/develop/package/devicetree.rst > > > > @@ -0,0 +1,583 @@ > > > > +.. SPDX-License-Identifier: GPL-2.0+ > > > > + > > > > +Updating the devicetree > > > > +======================= > > > > + > > > > +Note: This documentation describes how things are today,
mostly, with some
> > > > +mention of things that need to be fixed. It is not
intended to point the way to
> > > > +what might be done in the future. That should be the
subject of discussions on
> > > > +the mailing list. > > > > + > > > > +U-Boot uses devicetree for runtime configuration and
storing required blobs or
> > > > +any other information it needs to operate. It is possible
to update the
> > > > +devicetree separately from actually building U-Boot. This
provides a good degree
> > > > +of control and flexibility for firmware that uses U-Boot
in conjunction with
> > > > +other project. > > > > + > > > > +There are many reasons why it is useful to modify the
devicetree after building
> > > > +it: > > > > + > > > > +- Configuration can be changed, e.g. which UART to use > > > > +- A serial number can be added > > > > +- Public keys can be added to allow image verification > > > > +- Console output can be changed (e.g. to select serial or
vidconsole)
> > > > + > > > > +This section describes how to work with devicetree to
accomplish your goals.
> > > > + > > > > +See also :doc:`../devicetree/control` for a basic summary
of the available
> > > > +features. > > > > + > > > > + > > > > +Devicetree source > > > > +----------------- > > > > + > > > > +Every board in U-Boot must include a devicetree
sufficient to build and boot
> > > > +that board on suitable hardware (or emulation). This is
specified using the
> > > > +`CONFIG DEFAULT_DEVICE_TREE` option. > > > > + > > > > + > > > > +Current situation (August 2021) > > > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > + > > > > +As an aside, at present U-Boot allows
`CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> > > > +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are
used. This has
> > > > +unfortunately created an enormous amount of confusion and
some wasted effort.
> > > > +This was not intended and this bug will be fixed soon. > > > > + > > > > +Some of the problems created are: > > > > + > > > > +- It is not obvious that the devicetree is coming from
another project
> > > > + > > > > +- There is no way to see even a sample devicetree for
these platform in U-Boot,
> > > > + so it is hard to know what is going on, e.g. which
devices are typically
> > > > + present > > > > + > > > > +- The other project may not provide a way to support
U-Boot's requirements for
> > > > + devicetree, such as the /config node. Note: On the
U-Boot mailing list, this
> > > > + was only discovered after weeks of discussion and
confusion
> > > > + > > > > +- For QEMU specifically, consulting two QEMU source files
is required, for which
> > > > + there are no references in U-Boot documentation. The
code is generating a
> > > > + devicetree, with some control from command-line args,
but it is not clear
> > > > + how to add properties required by U-Boot. > > > > + > > > > +Specifically on the changes in U-Boot: > > > > + > > > > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry
Pi, which does have
> > > > + an in-tree devicetree, but this feature has since been
used for boards that
> > > > + don't > > > > +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part
of a larger Broadcom
> > > > + change with a tag indicating it only affected one
board, so the change in
> > > > + behaviour was not noticed at the time. It has since
been used by RISC-V qemu
> > > > + boards. > > > > + > > > > +Note: It is not clear that we actually need both of
these. Possibly
> > > > +`CONFIG_OF_BOARD` can be dropped. > > > > + > > > > +Once this bug is fixed, CONFIG_OF_BOARD and
CONFIG_OF_PRIOR_STAGE will override
> > > > > > What does "bug" refer to? Above you describe the current
design not a bug.
> > > > The bug is that we have two options to provide seemingly the
same
> > functionality. Is there a functional difference between
CONFIG_OF_BOARD
> > and CONFIG_OF_PRIOR_STAGE ? > > With CONFIG_OF_BOARD there is a function that returns the
pointer to
> the DTB, so you can do all sort of things with it. > > With CONFIG_OF_PRIOR_STAGE there is a variable that you need to
set in
> low-level code to point at the DTB and there is a pre-defined
function
> that returns that pointer. > > CONFIG_OF_BOARD is more flexible than CONFIG_OF_PRIOR_STAGE, but
if
> the only thing you want to do is to pass on a DTB that is passed
in a
> CPU register to U-Boot then CONFIG_OF_PRIOR_STAGE is probably
easier
> to use. > > I'm not convinced there is a bug here.
Thanks for explaining. Couldn't CONFIG_OF_PRIOR_STAGE be
rewritten as
an implementation of CONFIG_OF_BOARD, possibly at the same or less overall code size? That I think is the potential bug.
Probably a little bit more code:
void * board_fdt_blob_setup(void) { return (void *)(uintptr_t)prior_stage_fdt_address; }
Tiny bit more. Probably worth doing to make the choices clearer on which to select when? Bin, Rick, thoughts on this since riscv is the main user of CONFIG_OF_PRIOR_STAGE at this point?
Bin, Rick?
What is the prior stage in the RISC-V stage? Could we get it to set up a bloblist? Then we can add a devicetree in there, with the option to add more things in future.
I'm suggesting we don't need to do anything upstream of us, just rework things to use the other hook for "provided a DTB by caller, use it", so that we have a single hook for that.
-- Tom
What was the rationale in posting in kernel.org ( https://lore.kernel.org/all/20211003125134.2.I7733f5a849476e908cc51f0c71b8a5... ) and not in U-Boot knowing there is still no consensus on the big picture ?
Well, because we need to get our bindings reviewed and made official, and that looked like a reasonable place and choice to start with? v2 cc'd a different set of lists, at Rob's suggestion.
We agreed you would defer the device tree documentation patch you proposed because we did not agree on the painted overall picture. So I was surprised by your post. I agree standardization of U-Boot bindings is a good thing. Trustedfirnware.org does it internally and U-Boot can get inspiration from this. https://trustedfirmware-a.readthedocs.io/en/latest/components/cot-binding.ht...
Note that your example there should also be reviewed and sent upstream as the problem is less "U-Boot's config binding isn't documented" but more "U-Boot's config binding isn't official".