Re: [PATCH 0/2] Add rpi5 specific defconfig

[Rasmus Villemoes <ravi@prevas.dk>]

On Mon, May 05 2025, Tom Rini <trini@konsulko.com> wrote:

> On Mon, May 05, 2025 at 10:19:24PM +0200, Mark Kettenis wrote:
>> > Date: Mon, 5 May 2025 07:48:43 -0600
>> > From: Tom Rini <trini@konsulko.com>
>> > 
>> > On Mon, May 05, 2025 at 11:45:05AM +0200, Rasmus Villemoes wrote:
>> > > On Fri, May 02 2025, Tom Rini <trini@konsulko.com> wrote:
>> > > 
>> > > > On Fri, May 02, 2025 at 01:34:33PM +0200, Bruno Leite wrote:
>> > > >
>> > > >> From: Bruno Leite <brule@prevas.dk>
>> > > >> 
>> > > >> 
>> > > >> Currently rpi5 uses a generic rpi_arm64_defconfig file that builds rpi4
>> > > >> devicetree. Add a defconfig that is specific to the rpi5 building the
>> > > >> now available upstream dts for that board. The defconfig makes use of
>> > > >> defconfig including that is now available and only changes the DTS
>> > > >> related config.
>> > > >> 
>> > > >> It is also necessary to add a more specific u-boot.dtsi to rpi5, since
>> > > >> due to the ARCH_BCM283X config it will try to build the
>> > > >> bcm283x-u-boot.dtsi and break.
>> > > >
>> > > > My question is, can we not adjust rpi_arm64_defconfig to be generic
>> > > > enough and not have a problem on Pi 5 due to the default device tree?
>> > > 
>> > > Not really.
>> > > 
>> > > What we want is to have CONFIG_DEFAULT_DEVICE_TREE to point at the
>> > > rpi5's .dts file, because we really want to build that and not some
>> > > "random" dts file that doesn't have anything to do with the hardware. I
>> > > know that kinda works for the setups where the .dtb built in U-Boot is
>> > > not used for anything, but in our case, we really do want to use the
>> > > .dtb from the U-Boot build - we inject various U-Boot specific stuff via
>> > > the EXTRA_DTSI mechanism, e.g. public key for kernel verification.
>> > > 
>> > > And due to CONFIG_SYS_SOC being bcm283x, and bcm283x-u-boot.dtsi
>> > > referencing nodes that simply don't exist when building
>> > > bcm2712-rpi-5-b.dts, the build breaks.
>> > > 
>> > > Perhaps the real problem is CONFIG_SYS_SOC being bcm283x for rpi5? I
>> > > don't really know why rpi4 is both bcm2711 and bcm2835 and what the
>> > > difference is, but rpi5 only seems to include a bcm2712.dtsi which does
>> > > not include further dtsi files.
>> > > 
>> > > If rpi5 has nothing to do with bcm283x, then perhaps a better approach
>> > > is to ensure that CONFIG_SYS_SOC is bcm2712 when building for
>> > > rpi5. Something like adding a CONFIG_TARGET_RPI_5 choice and adding a
>> > > 'default "bcm2712" if TARGET_RPI_5' ?
>> > 
>> > OK, so I guess my next question is, is rpi_arm64 useful enough in the
>> > end for Pi 3 and Pi 4? I would have expected that it doesn't matter what
>> > tree we build in to U-Boot as we would be using the one passed to us by
>> > the prior stage firmware, and then update that at run-time as needed.
>> 
>> Works well enough for us on OpenBSD.  And it would be nice if
>> rpi_arm64 would work for the Pi 5 as well.
>
> But that gets back to my first question. Can we correct the code such
> that we do whatever is required at run time, as the previous stage will
> have assembled and passed a correct device tree already?

I think this is sort-of asking the wrong question. The problem is not
about what dtb the prior stage hands us or what to do at run-time. [*]

The problem is to have a defconfig that will compile
bcm2712-rpi-5-b.dts, as part of the U-Boot build. As I said, it's quite
likely that rpi5 isn't at all a part of the 'menu "Broadcom BCM283X
family"', and it's the CONFIG_SYS_SOC="bcm283x" that prevents
bcm2712-rpi-5-b.dts from being compiled (because the bcm283x-u-boot.dtsi
doesn't apply to that .dts). Bruno's patches achieve that by adding a
more-specific -u-boot.dtsi file (it doesn't seem that we need any of the
bootph-all settings from the bcm283x.dtsi file), and adding a defconfig
file that is based on arm64, but just changes the dt settings.

Those who simply ignore what .dtbs are part of the U-Boot build and use
blobs coming from elsewhere can probably use rpi_arm64_defconfig as-is
for rpi5.

Rasmus

[*] That's mostly a solved packaging problem outside the scope of
U-Boot itself: Just put whatever .dtb one wishes the prior stage to pass
to U-Boot along with u-boot.bin in the FAT filesystem, and put

kernel=u-boot.bin
device_tree=u-boot.dtb

in config.txt (sure, there might be drivers that need updating to take
different compatibles or whatnot into account).