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

[Simon Glass]

Hi Tom,

On Sun, Dec 31, 2023 at 7:01 AM Tom Rini <trini at konsulko.com> wrote:
>
> 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.

Think about firmware update where you could have an update that
supports all rk3399 boards, rather than 110 separate (and duplicate)
firmware updates.

> 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.

We'll see. The size cost for making things generic across an SoC is
likely very small, particularly if the settings are in the DT where
they belong. But I do accept we are not seeing the pressure yet.

For XPL, there are pros and cons, but I thought we talked about that
at the time and agreed that the need for Kconfig dependencies between
phases makes having separate defconfigs too painful?

Regards,
Simon