On 10/27/21 15:15, François Ozog wrote:
Hi,
On Wed, 27 Oct 2021 at 14:48, Tom Rini <tr...@konsulko.com
<mailto:tr...@konsulko.com>> wrote:
On Fri, Oct 15, 2021 at 12:03:44PM -0600, Simon Glass wrote:
> Hi all,
>
> On Thu, 14 Oct 2021 at 09:28, Tom Rini <tr...@konsulko.com
<mailto:tr...@konsulko.com>> wrote:
> >
> > On Thu, Oct 14, 2021 at 09:17:52AM -0600, Simon Glass wrote:
> > > Hi Tom,
> > >
> > > On Thu, 14 Oct 2021 at 08:56, Tom Rini <tr...@konsulko.com
<mailto:tr...@konsulko.com>> wrote:
> > > >
> > > > On Wed, Oct 13, 2021 at 12:06:02PM -0600, Simon Glass wrote:
> > > > > Hi François,
> > > > >
> > > > > On Wed, 13 Oct 2021 at 11:35, François Ozog
<francois.o...@linaro.org <mailto:francois.o...@linaro.org>> wrote:
> > > > > >
> > > > > > Hi Simon
> > > > > >
> > > > > > Le mer. 13 oct. 2021 à 16:49, Simon Glass
<s...@chromium.org <mailto:s...@chromium.org>> a écrit :
> > > > > >>
> > > > > >> Hi Tom, Bin,François,
> > > > > >>
> > > > > >> On Tue, 12 Oct 2021 at 19:34, Tom Rini
<tr...@konsulko.com <mailto:tr...@konsulko.com>> wrote:
> > > > > >> >
> > > > > >> > On Wed, Oct 13, 2021 at 09:29:14AM +0800, Bin Meng
wrote:
> > > > > >> > > Hi Simon,
> > > > > >> > >
> > > > > >> > > On Wed, Oct 13, 2021 at 9:01 AM Simon Glass
<s...@chromium.org <mailto:s...@chromium.org>> wrote:
> > > > > >> > > >
> > > > > >> > > > With Ilias' efforts we have dropped
OF_PRIOR_STAGE and OF_HOSTFILE so
> > > > > >> > > > there are only three ways to obtain a devicetree:
> > > > > >> > > >
> > > > > >> > > > - OF_SEPARATE - the normal way, where the
devicetree is built and
> > > > > >> > > > appended to U-Boot
> > > > > >> > > > - OF_EMBED - for development purposes, the
devicetree is embedded in
> > > > > >> > > > the ELF file (also used for EFI)
> > > > > >> > > > - OF_BOARD - the board figures it out on its own
> > > > > >> > > >
> > > > > >> > > > The last one is currently set up so that no
devicetree is needed at all
> > > > > >> > > > in the U-Boot tree. Most boards do provide one,
but some don't. Some
> > > > > >> > > > don't even provide instructions on how to boot
on the board.
> > > > > >> > > >
> > > > > >> > > > The problems with this approach are documented
at [1].
> > > > > >> > > >
> > > > > >> > > > In practice, OF_BOARD is not really distinct
from OF_SEPARATE. Any board
> > > > > >> > > > can obtain its devicetree at runtime, even it is
has a devicetree built
> > > > > >> > > > in U-Boot. This is because U-Boot may be a
second-stage bootloader and its
> > > > > >> > > > caller may have a better idea about the hardware
available in the machine.
> > > > > >> > > > This is the case with a few QEMU boards, for
example.
> > > > > >> > > >
> > > > > >> > > > So it makes no sense to have OF_BOARD as a
'choice'. It should be an
> > > > > >> > > > option, available with either OF_SEPARATE or
OF_EMBED.
> > > > > >> > > >
> > > > > >> > > > This series makes this change, adding various
missing devicetree files
> > > > > >> > > > (and placeholders) to make the build work.
> > > > > >> > >
> > > > > >> > > Adding device trees that are never used sounds
like a hack to me.
> > > > > >> > >
> > > > > >> > > For QEMU, device tree is dynamically generated on
the fly based on
> > > > > >> > > command line parameters, and the device tree you
put in this series
> > > > > >> > > has various hardcoded <phandle> values which
normally do not show up
> > > > > >> > > in hand-written dts files.
> > > > > >> > >
> > > > > >> > > I am not sure I understand the whole point of this.
> > > > > >> >
> > > > > >> > I am also confused and do not like the idea of
adding device trees for
> > > > > >> > platforms that are capable of and can / do have a
device tree to give us
> > > > > >> > at run time.
> > > > > >>
> > > > > >> (I'll just reply to this one email, since the same
points applies to
> > > > > >> all replies I think)
> > > > > >>
> > > > > >> I have been thinking about this and discussing it with
people for a
> > > > > >> few months now. I've been signalling a change like
this for over a
> > > > > >> month now, on U-Boot contributor calls and in
discussions with Linaro
> > > > > >> people. I sent a patch (below) to try to explain
things. I hope it is
> > > > > >> not a surprise!
> > > > > >>
> > > > > >> The issue here is that we need a devicetree in-tree in
U-Boot, to
> > > > > >> avoid the mess that has been created by
OF_PRIOR_STAGE, OF_BOARD,
> > > > > >> BINMAN_STANDALONE_FDT and to a lesser extent,
OF_HOSTFILE. Between
> > > > > >> Ilias' series and this one we can get ourselves on a
stronger footing.
> > > > > >> There is just OF_SEPARATE, with OF_EMBED for
debugging/ELF use.
> > > > > >> For more context:
> > > > > >>
> > > > > >>
http://patchwork.ozlabs.org/project/uboot/patch/20210919215111.3830278-3-...@chromium.org/
<http://patchwork.ozlabs.org/project/uboot/patch/20210919215111.3830278-3-...@chromium.org/>
> > > > > >>
> > > > > >> BTW I did suggest to QEMU ARM that they support a way
of adding the
> > > > > >> u-boot.dtsi but there was not much interest there (in
fact the
> > > > > >> maintainer would prefer there was no special support
even for booting
> > > > > >> Linux directly!)
> > > > > >
> > > > > > i understand their point of view and agree with it.
> > > > > >>
> > > > > >> But in any case it doesn't really help U-Boot. I
> > > > > >> think the path forward might be to run QEMU twice,
once to get its
> > > > > >> generated tree and once to give the 'merged' tree with
the U-Boot
> > > > > >> properties in it, if people want to use U-Boot features.
> > > > > >>
> > > > > >> I do strongly believe that OF_BOARD must be a run-time
option, not a
> > > > > >> build-time one. It creates all sorts of problems and
obscurity which
> > > > > >> have taken months to unpick. See the above patch for
the rationale.
> > > > > >>
> > > > > >> To add to that rationale, OF_BOARD needs to be an
option available to
> > > > > >> any board. At some point in the future it may become a
common way
> > > > > >> things are done, e.g. TF-A calling U-Boot and
providing a devicetree
> > > > > >> to it. It doesn't make any sense to have people decide
whether or not
> > > > > >> to set OF_BOARD at build time, thus affecting how the
image is put
> > > > > >> together. We'll end up with different U-Boot build
targets like
> > > > > >> capricorn, capricorn_of_board and the like. It should
be obvious where
> > > > > >> that will lead. Instead, OF_BOARD needs to become a
commonly used
> > > > > >> option, perhaps enabled by most/all boards, so that
this sort of build
> > > > > >> explosion is not needed.
> > > > > >
> > > > > > If you mean that when boards are by construction
providing a DTB to U-Boot then I agree very much. But I don’t
understand how the patch set supports it as it puts dts files for
those boards to be built.
> > > > > >>
> > > > > >> U-Boot needs to be flexible enough to
> > > > > >> function correctly in whatever runtime environment in
which it finds
> > > > > >> itself.
> > > > > >>
> > > > > >> Also as binman is pressed into service more and more
to build the
> > > > > >> complex firmware images that are becoming fashionable,
it needs a
> > > > > >> definition (in the devicetree) that describes how to
create the image.
> > > > > >> We can't support that unless we are building a
devicetree, nor can the
> > > > > >> running program access the image layout without that
information.
> > > > > >>
> > > > > >> François's point about 'don't use this with any kernel' is
> > > > > >> germane...but of course I am not suggesting doing
that, since OF_BOARD
> > > > > >> is, still, enabled. We already use OF_BOARD for
various boards that
> > > > > >> include an in-tree devicetree - Raspberry Pi 1, 2 and
3, for example
> > > > > >> (as I said in the cover letter "Most boards do provide
one, but some
> > > > > >> don't."). So this series is just completing the
picture by enforcing
> > > > > >> that *some sort* of devicetree is always present.
> > > > > >
> > > > > > That seems inconsistent with the OF_BOARD becomes the
default.
> > > > >
> > > > > I think the key point that will get you closer to where I
am on this
> > > > > issue, is that OF_BOARD needs to be a run-time option. At
present it
> > > > > has build-time effects and this is quite wrong. If you go
through all
> > > > > the material I have written on this I think I have
motivated that very
> > > > > clearly.
> > > > >
> > > > > Another big issue is that I believe we need ONE
devicetree for U-Boot,
> > > > > not two that get merged by U-Boot. Again I have gone
through that in a
> > > > > lot of detail.
> > > >
> > > > I have a long long reply to your first reply here saved,
but, maybe
> > > > here's the biggest sticking point. To be clear, you agree
that U-Boot
> > > > needs to support being passed a device tree to use, at run
time, yes?
> > >
> > > Yes. The OF_BOARD feature provides this.
> > >
> > > >
> > > > And in that case, would not be using the "fake" tree we
built in?
> > >
> > > Not at runtime.
> >
> > OK.
> >
> > > > So is the sticking point here that we really have two
classes of
> > > > devices, one class where we will never ever be given the
device tree at
> > > > run time (think BeagleBone Black) and one where we will
always be given
> > > > one at run time (think Raspberry Pi) ?
> > >
> > > I'm not sure it will be that black and white. I suspect there
will be
> > > (many) boards which can boot happily with the U-Boot
devicetree but
> > > can also accept one at runtime, if provided. For example, you
may want
> > > to boot with or without TF-A or some other, earlier stage.
> >
> > I'm not sure I see the value in making this a gray area.
There's very
> > much a class of "never" boards. There's also the class of
"can" today.
> > Maybe as part of a developer iterative flow it would be nice to
not have
> > to re-flash the prior stage to change a DT, and just do it in
U-Boot
> > until things are happy, but I'm not sure what the use case is for
> > overriding the previous stage.
> >
> > Especially since the pushback on this series I think has all
been "why
> > are we copying in a tree to build with? We don't want to use
it at run
> > time!". And then softer push back like "Well, U-Boot says we
have to
> > include the device tree file here, but we won't use it...".
>
> See below.
>
> >
> > > I believe we have got unstuck because OF_BOARD (perhaps
inadvertently)
> > > provided a way to entirely omit a devicetree from U-Boot,
thus making
> > > things like binman and U-Boot /config impossible, for
example. So I
> > > want to claw that back, so there is always some sort of
devicetree in
> > > U-Boot, as we have for rpi_3, etc.
> >
> > I really want to see what the binary case looks like since we
could then
> > kill off rpi_{3,3_b,4}_defconfig and I would need to see if we
could
> > then also do a rpi_arm32_defconfig too.
> >
> > I want to see less device trees in U-Boot sources, if they can come
> > functionally correct from the hardware/our caller.
> >
> > And I'm not seeing how we make use of "U-Boot /config" if we
also don't
> > use the device tree from build time at run time, ignoring the
device
> > tree provided to us at run time by the caller.
>
> Firstly I should say that I find building firmware very messy and
> confusing these days. Lots of things to build and it's hard to find
> the instructions. It doesn't have to be that way, but if we carry on
> as we are, it will continue to be messy and in five years you will
> need a Ph.D and a lucky charm to boot on any modern board. My
> objective here is to simplify things, bringing some consistency
to the
> different components. Binman was one effort there. I feel that
putting
> at least the U-Boot house in order, in my role as devicetree
> maintainer (and as author of devicetree support in U-Boot back in
> 2011), is the next step.
Yes, it's Not Great. I don't like my handful of build-BOARD.sh scripts
that know where to grab other known-good binaries of varying licenses
that are needed to assemble something that boots.
> If we set things up correctly and agree on the bindings, devicetree
> can be the unifying configuration mechanism through the whole of
> firmware (except for very early bits) and into the OS, this will set
> us up very well to deal with the complexity that is coming.
>
> Anyway, here are the mental steps that I've gone through over the
past
> two months:
>
> Step 1: At present, some people think U-Boot is not even allowed to
> have its own nodes/properties in the DT.
In my view U-Boot shall be able to leverage device tree format (source
and binary) to store its own data.
When you say "the" DT, I always think this is "the" DT that is passed to
OS and in "that" DT, there should be no U-Boot entries. As stated in
another mail thread, I also refer to a place in a FIP where that dynamic
config DT is meant to be stored: NT_FW_CONFIG.
But there can be U-Boot defined bindings in "a" control/dynamic config
DT; Trusted Firmware does that.
It ends up in that we need two separate devicetrees.
One passed to U-Boot for fixups and further passed to the OS. This
devicetree may originate from a prior boot stage, from a file loaded by
U-Boot, or from a later bootstage, e.g systemd-boot's devicetree
command. This devicetree will not contain any U-Boot specific information.
A second devicetree to hold everything that U-Boot needs for its
internal purposes.
Best regards
Heinrich
It is an abuse of the
> devicetree standard, like the /chosen node but with less history. We
> should sacrifice efficiency, expedience and expandability on the
altar
> of 'devicetree is a hardware description'. How do we get over that
> one? Wel, I just think we need to accept that U-Boot uses devicetree
> for its own purposes, as well as for booting the OS. I am not saying
Yes, we need to have properties present in the device tree, and just
like how "linux," is a valid vendor prefix for the linux kernel (but not
used I would expect by the BSD families) we have cases that need
"u-boot," properties.
> it always has to have those properties, but with existing features
> like verified boot, SPL as well as complex firmware images where
> U-Boot needs to be able to find things in the image, it is essential.
> So let's just assume that we need this everywhere, since we certainly
> need it in at least some places.
No, we can't / shouldn't assume we need this everywhere. A lot of
places? Yes. But some features are going to be optional. A valid must
be supported use case is something like a Pi where the hardware gives us
a device tree, the tree is correct and some features in U-Boot aren't
needed (SPL) nor possibly supported immediately (verified boot). We can
go off on a tangent about how useful it would be to have HW platforms
that are both common and can demonstrate a number of features, but
that's its own problem to solve.
> (stop reading here if you disagree, because nothing below will make
> any sense...you can still use U-Boot v2011.06 which doesn't have
> OF_CONTROL :-)
>
> Step 2: Assume U-Boot has its own nodes/properties. How do they get
> there? Well, we have u-boot.dtsi files for that (the 2016 patch
> "6d427c6b1fa binman: Automatically include a U-Boot .dtsi file"), we
> have binman definitions, etc. So we need a way to overlay those
things
> into the DT. We already support this for in-tree DTs, so IMO this is
> easy. Just require every board to have an in-tree DT. It helps with
> discoverability and documentation, anyway. That is this series.
>
> (I think most of us are at the beginning of step 2, unsure about it
> and worried about step 3)
>
> Step 3: Ah, but there are flows (i.e. boards that use a particular
> flow only, or boards that sometimes use a flow) which need the DT to
> come from a prior stage. How to handle that? IMO that is only
going to
> grow as every man and his dog get into the write-a-bootloader
> business. We need a way to provide the U-Boot nodes/properties in a
> form that the prior stage can consume and integrate with its build
> system. Is TF-A the only thing being discussed here? If so, let's
just
> do it. We have the u-boot.dtsi and we can use binman to put the image
> together, for example. Or we can get clever and create some sort of
> overlay dtb.
>
> Step 3a. But I don't want to do that. a) If U-Boot needs this stuff
> then it will need to build it in and use two devicetrees, one
internal
> and one from the prior stage....well that is not very efficient
and it
> is going to be confusing for people to figure out what U-Boot is
> actually doing. But we actually already do that in a lot of cases
> where U-Boot passes a DT to the kernel which is different to the one
> it uses. So perhaps we have three devicetrees? OMG. b) Well then
> U-Boot can have its own small devicetree with its bits and then
U-Boot
> can merge the two when it starts. Again that is not very efficient.
Does not need to merge the two. hence it does not have any influence on
efficiency.
For properties access, trusted firmware has defined an abstract way to
get them:
https://trustedfirmware-a.readthedocs.io/en/latest/components/fconf/index.html
<https://trustedfirmware-a.readthedocs.io/en/latest/components/fconf/index.html>.
The properties are currently implemented as DT but TF.ORG
<http://TF.ORG> could decide to move to CBOR.
The API will remain so that a change in backend will not influence
existing code.
I think you are too focused on "THE" device tree. "THE" device tree that
is passed to the OS
shall be hardware description and not a hacky place to fit any piece of
metadata.
I would argue that /chosen shall not even be there as most if not all
information can be passed as OS command line. And actually for the UEFI
contract, /chosen should go empty.
It
> means that U-Boot cannot be controlled by the prior stage (e.g.
to get
> its public key from there or to enable/disable the console), so
> unified firmware config is not possible. It will get very confusing,
> particularly for debugging U-Boot. c) Some other scheme to avoid
> accepting step 3...please stop!
How the nodes should get there is how the rest of the nodes in a system
get there. Bindings are submitted and reviewed. The authoritative
source of the dtses in question then has them, like any other property.
> Step 4: Yes, but there is QEMU, which makes the devicetree up out of
> whole cloth. What about that? Well, we are just going to have to deal
> with that. We can easily merge in the U-Boot nodes/properties and
> update the U-Boot CI scripts to do this, as needed, e.g. with
> qemu-riscv64_spl. It's only one use case, although Xen might do
> something similar.
>
> To my mind, that deals with both the build-time and run-time issues.
> We have a discoverable DT in U-Boot, which should be considered the
> source of truth for most boards. We can sync it with Linux
> automatically with the tooling that I hope Rob Herring will come up
> with. We can use an empty one where there really is no default,
> although I'd argue that is making perfect an enemy of the good.
>
> Step 5: If we get clever and want to remove them from the U-Boot tree
> and pick them up from somewhere else, we can do that with sufficient
> tooling. Perhaps we should set a timeline for that? A year? Two? Six?
For SystemReady compliant boards, this has to come much faster.
Do you think distros will keep providing DTs for ever? I bet not.
These last two paragraphs condense what I think is honestly close to a
decade of debate / discussion down to a fiat "U-Boot will have the DTS
files". I don't want that. I don't think any of the other projects
that want to leverage DTS files want that.
> To repeat, if we set things up correctly and agree on the bindings,
> devicetree can be the unifying configuration mechanism through the
> whole of firmware (except for very early bits) and into the OS. I
feel
> this will set us up very well to deal with the complexity that is
> coming.
Sure, it could. But that doesn't mean that U-Boot is where the dts
files live.
--
Tom
--
François-Frédéric Ozog | /Director Business Development/
T: +33.67221.6485
francois.o...@linaro.org <mailto:francois.o...@linaro.org> | Skype: ffozog
