[PATCH] arm: Add (back) VExpress boards support

[Tom Rini]

On Tue, Jun 29, 2021 at 05:52:10PM +0100, Andre Przywara wrote:
> On Tue, 29 Jun 2021 15:15:52 +0100
> Andre Przywara <andre.przywara at arm.com> wrote:
> 
> Hi,
> 
> > On Tue, 29 Jun 2021 08:11:22 -0400
> > Tom Rini <trini at konsulko.com> wrote:
> > 
> > > On Tue, Jun 29, 2021 at 12:45:55PM +0100, Andre Przywara wrote:
> > >   
> > > > The v2021.07 merge window saw the removal of the Arm Ltd. Versatile
> > > > Express platform, along with their CA5, CA9 and TC2 boards. The trigger
> > > > was the missing conversion of the MMC driver.
> > > > 
> > > > Some folks complained about that internally, so bring those boards back,
> > > > but better than ever:
> > > > - Use DM and OF_CONTROL for all the boards. Use the .dts files from the
> > > >   latest Linux kernel (5.13) for that.
> > > > - Move the board selection choice into the platform's Kconfig.
> > > > - Clean up some shared config and common definitions.
> > > > - Drop obsolete features like ATAGs support.
> > > > - Switch to the DM_ETH version of the SMC911X Ethernet driver.
> > > > - Drop MMC support.
> > > > 
> > > > The PL180 MMC driver actually supports DM_MMC, but that requires a
> > > > DM_GPIO driver for the card detect GPIO, which we don't have. This
> > > > specific GPIO is actually handled via the "sysregs" device, so we would
> > > > need a driver for that. QEMU does not emulate this part, also the DT
> > > > description is somewhat "special", so this is left for later.
> > > > 
> > > > This version compiles without any warning for all three boards now.
> > > > Tested on QEMU.
> > > > 
> > > > Signed-off-by: Andre Przywara <andre.przywara at arm.com>
> > > > ---
> > > > Hi,
> > > > 
> > > > this relies on the SMC911x driver DT changes, as posted here:
> > > > https://lists.denx.de/pipermail/u-boot/2021-June/452989.html
> > > > I put a version with the changes broken down here:
> > > > https://github.com/Andre-ARM/u-boot/commits/tc2-history
> > > > 
> > > > This was tested on QEMU, for vexpress_ca15_tc2_defconfig with:
> > > > $ qemu-system-arm -M vexpress-a15,secure=on -cpu cortex-a15 -m 1G -smp 1 \
> > > >   -drive file=tramp-tc2.bin,if=pflash,format=raw,read-only \
> > > >   -device loader,file=u-boot.bin,addr=0x80800000 -nographic
> > > > 
> > > > Where tramp-tc2.bin is a trampoline replacing the board's firmware:
> > > > 00000000  00 00 a0 e3 80 00 48 e3  10 ff 2f e1
> > > > (mov r0, #0; movt r0, #0x8080; bx r0)
> > > > 
> > > > The vexpress_ca9x4_defconfig uses a different memory map, so the runes are:
> > > > $ qemu-system-arm -M vexpress-a9 -cpu cortex-a9 -m 1G -smp 1 \
> > > >   -drive file=tramp-ca9.bin,if=pflash,format=raw,read-only \
> > > >   -device loader,file=u-boot.bin,addr=0x60800000 -nographic
> > > > 
> > > > tramp-ca9.bin:
> > > > 00000000  00 00 a0 e3 80 00 46 e3  10 ff 2f e1
> > > > (mov r0, #0; movt r0, #0x6080; bx r0)    
> > > 
> > > My big question is how do we run this in CI?  Or does it not _need_ that
> > > firmware file to really exist?  Or is there a pending change to
> > > https://gitlab.denx.de/u-boot/u-boot-test-hooks.git to generate / just
> > > have exist those magic empty bins?  Thanks!  
> > 
> > So from digging into this I see that this loads U-Boot's ELF build, via
> > QEMU's -kernel parameter. Which is fine, but not really what is
> > happening on real hardware.
> > I checked and the v2021.04 version worked with this approach, but my
> > build does not.
> > I will have a look into this now.
> 
> The new build uses OF_CONTROL and OF_SEPARATE, so the DTB gets appended
> to the U-Boot *image*. The ELF file is not treated this way, so the
> code reads only 0s after the end of the U-Boot code - which makes it
> die silently. Manually loading the DTB into DRAM would be fragile at
> best, but is also rejected by QEMU, because the LOAD program header
> extend for a few dozen bytes beyond U-Boot's "end" symbol, so it
> overlaps.

Can't we pass the device tree to qemu (and in turn through to U-Boot) in
a clean and out of the box way?  I thought there was a way to do that..

> IIRC we don't have position independent code for ARM, so we can't load
> U-Boot into flash directly (which also would require some code changes
> first).

Do you mean generate a file to use as the system flash and have U-Boot
be in the correct spot within that file?  If so
bin/travis-ci/conf.qemu_mips_na in the test hooks repo might give you
some hints.

> Anyway I don't think we should change any code to cope with that (by
> using another method to find the DTB), so adjusting the QEMU recipe
> sounds like a better idea.
> 
> Is there a way to add those 12 byte trampoline files to the CI repo? Or
> shall they be created on the fly somehow?

If we need to include the trampoline files, however it's easiest is
fine.

-- 
Tom
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