[PATCH 0/9] dts: Move to SoC-specific build rules

[Tom Rini]

On Sun, Dec 31, 2023 at 05:45:00AM -0700, Simon Glass wrote:
> -Scott as it is bouncing
> 
> Hi,
> 
> On Fri, Dec 29, 2023 at 9:46 AM Peter Robinson <pbrobinson at gmail.com> wrote:
> >
> > On Fri, Dec 29, 2023 at 12:23 AM Tom Rini <trini at konsulko.com> wrote:
> > >
> > > On Thu, Dec 28, 2023 at 07:48:08PM +0000, Simon Glass wrote:
> > > > Hi Tom,
> > > >
> > > > On Thu, Dec 28, 2023 at 3:40 PM Tom Rini <trini at konsulko.com> wrote:
> > > > >
> > > > > On Thu, Dec 28, 2023 at 03:09:40PM +0000, Simon Glass wrote:
> > > > > > Hi Tom,
> > > > > >
> > > > > > On Thu, Dec 28, 2023 at 2:23 PM Tom Rini <trini at konsulko.com> wrote:
> > > > > > >
> > > > > > > On Thu, Dec 28, 2023 at 01:37:07PM +0000, Simon Glass wrote:
> > > > > > > > Hi Tom,
> > > > > > > >
> > > > > > > > On Wed, Dec 27, 2023 at 1:21 PM Tom Rini <trini at konsulko.com> wrote:
> > > > > > > > >
> > > > > > > > > On Wed, Dec 27, 2023 at 08:23:56AM +0000, Simon Glass wrote:
> > > > > > > > >
> > > > > > > > > > U-Boot builds devicetree binaries from its source tree. As part of the
> > > > > > > > > > Kconfig conversion, the Makefiles were updated to align with how this
> > > > > > > > > > is done in Linux: a single target for each SoC is used to build all the
> > > > > > > > > > .dtb files for that SoC.
> > > > > > > > > >
> > > > > > > > > > Since then, the Makefiles have devolved in some cases, resulting in
> > > > > > > > > > lots of target-specific build rules. Also Linux has moved to using
> > > > > > > > > > subdirectories for each vendor.
> > > > > > > > > >
> > > > > > > > > > Recent work aims to allow U-Boot to directly use devicetree files from
> > > > > > > > > > Linux. This would be easier if the directory structure were the same.
> > > > > > > > > > Another recent discussion involved dropping the build rules altogether.
> > > > > > > > > >
> > > > > > > > > > This series makes a start at cleaning up some of the build rules, to
> > > > > > > > > > reduce the amount of code and make it easier to add new boards for the
> > > > > > > > > > same SoC.
> > > > > > > > > >
> > > > > > > > > > One issue is that the ARCH_xxx Kconfig options between U-Boot and Linux
> > > > > > > > > > are not always the same. Given the large number of SoCs and boards
> > > > > > > > > > supported by U-Boot, it would be useful to align these where possible.
> > > > > > > > >
> > > > > > > > > I don't know why we should start with this now, and further not being on
> > > > > > > > > top of Sumit's series to remove our duplicate dts files. And that's
> > > > > > > > > where we can have the conversation about for which cases it even makes
> > > > > > > > > sense to build all of the dts files for a given SoC.
> > > > > > > >
> > > > > > > > This is a completely different series - there are no conflicts with
> > > > > > > > Sumit's series so it can be applied before or after it.
> > > > > > > >
> > > > > > > > My goal here is to clean up our build rules, rather than just throwing
> > > > > > > > them all away, for reasons we have discussed previously. I filed [1]
> > > > > > > > to track that.
> > > > > > >
> > > > > > > Yes, I'm saying we shouldn't be doing anything this series does until
> > > > > > > after Sumit's series has landed. Along with the fact that I don't like
> > > > > > > what's going on in this series.
> > > > > >
> > > > > > This seems to again be the disagreement over whether a single DT
> > > > > > should be build for each board, or all the DTs for an SoC?
> > > > >
> > > > > It's about the disagreement on what we should be building, and what that
> > > > > infrastructure looks like. I do not like adding extra rules for
> > > > > "clarity" because they don't make things clearer, they lead to the
> > > > > unclear mess we have today getting worse. Most instructions are _not_
> > > > > "now take this dtb and this binary and .." but just "take this binary",
> > > > > because we already have the rules and logic to ensure we build the
> > > > > required dtbs. I also don't like the parts of this series that amount
> > > > > to deck shuffling when we should just be taking the chairs away. There's
> > > > > just not nor will there be a case for omap3/4/5 platforms of "change the
> > > > > dtb", so building more is pointless. For other SoCs, there may be some
> > > > > cases of "this could have been just a DT change", like
> > > > > rock5b-rk3588_defconfig / rock5a-rk3588s_defconfig could share a board
> > > > > dir, but the configs are different and the dts are different, so I don't
> > > > > know that you could really just swap the dtbs.
> > > >
> > > > It is true that we have a different defconfig for each board, but IMO
> > > > that is not good. It is an artifact of the way the build system works.
> > > > IMO Kconfig should be used to define sensible defaults so that the
> > > > defconfigs are nearly empty. Perhaps config fragments can be part of
> > > > the mix, if we can agree on [1].
> > > >
> > > > But if we let this genie out of the bottle, it will be impossible to
> > > > put back in. The devicetree should control the hardware in U-Boot and
> > > > it should be possible to use the same U-Boot proper on all boards
> > > > which use the same SoC.
> > >
> > > We've never been past the point where a few examples of closely related
> > > boards can re-use the same U-Boot build and just change the device tree.
> > >
> > > It's going to be very SoC specific if we can ever do things like that,
> > > and it will also likely in turn become a question of where did the
> > > tricky bits that U-Boot used to do get shoved instead. You're not going
> > > to combine board/beagle/beagle/beagle.c and board/ti/omap3evm/evm.c (and
> > > ignoring all of the other omap3 boards) and get one binary that works on
> > > both, and just uses DT. Let alone that no one wants to do that work.
> > >
> > > You've mentioned Rockchip before as maybe a better example, but
> > > https://patchwork.ozlabs.org/project/uboot/list/?series=383579&state=* was
> > > leading me to think that no, there's too much "this is what THIS
> > > hardware does" that means that no, there's going to be hardware
> > > variation that one must just handle in C. Or get more and new bindings
> > > accepted upstream to try and make that be data driven, and also possibly
> > > have to deal with "that's policy, not hardware" type arguments and so
> > > forth.
> 
> Oh wow yes that is crazy! But you can always check the compatible
> string if really necessary. It would be nice to use a sysinfo driver
> for this sort of thing. I should just be a full-time code reviewer...
> 
> >
> > Related I've seen issues with nearly identical rockchips devices that
> > use different memory chips that as a result need different U-Boot
> > builds because the early boot part needs to initialise a completely
> > different set of memory and the two different sets of rules aren't
> > detectable at run-time nor are they even small enough to fit into
> > smem.
> 
> Some of the differences are real/important, like memory settings, some
> are not. For boards with enough SRAM that SPL can use DM/DT, we can
> deal with these.
> 
> But even if SPL does need to be custom, that is better than having a
> full, separate U-Boot for every single board.

I'm not sure that's a use case anyone else has or wants, and I disagree
that building a unique SPL and then more generic U-Boot is a win, in
practical and effort terms. The only win I see there is it would be part
of what I've said before about how I do not want the "XPL" series you've
talked about before, but instead think Yamada-san was right in hindsight
and in short we should have "fooboard_defconfig",
"fooboard_spl_defconfig" and "fooboard_tpl_defconfig" and you make each
config and build each config by itself. In that context, yes, you could
have barvend-fooboard_rev1_spl_defconfig,
barvend-fooboard_rev2_spl_defconfig and barvend-fooboard_defconfig to
get a more generic U-Boot build.  But nothing so much like an OS kernel
because we care about binary size and rarely does the OS vendor (but
some production cases in turn do), so outside of SoC-vendor where
showing off features is more important than size, most of the time, will
you see an actual use for SoC-generic U-Boot build.

-- 
Tom
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