linux-kernel - Re: [PATCH v5 01/13] powerpc: Remove Xilinx PPC405/PPC440 support

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Date:   Fri, 19 Jun 2020 21:02:53 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Michal Simek <michal.simek@...inx.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Arnd Bergmann <arnd@...db.de>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH v5 01/13] powerpc: Remove Xilinx PPC405/PPC440 support

Nathan Chancellor <natechancellor@...il.com> writes:
> On Thu, Jun 18, 2020 at 10:48:21AM +1000, Michael Ellerman wrote:
>> Nick Desaulniers <ndesaulniers@...gle.com> writes:
>> > On Wed, Jun 17, 2020 at 3:20 AM Michael Ellerman <mpe@...erman.id.au> wrote:
>> >> Michael Ellerman <mpe@...erman.id.au> writes:
>> >> > Michal Simek <michal.simek@...inx.com> writes:
>> >> <snip>
>> >>
>> >> >> Or if bamboo requires uImage to be built by default you can do it via
>> >> >> Kconfig.
>> >> >>
>> >> >> diff --git a/arch/powerpc/platforms/44x/Kconfig
>> >> >> b/arch/powerpc/platforms/44x/Kconfig
>> >> >> index 39e93d23fb38..300864d7b8c9 100644
>> >> >> --- a/arch/powerpc/platforms/44x/Kconfig
>> >> >> +++ b/arch/powerpc/platforms/44x/Kconfig
>> >> >> @@ -13,6 +13,7 @@ config BAMBOO
>> >> >>         select PPC44x_SIMPLE
>> >> >>         select 440EP
>> >> >>         select FORCE_PCI
>> >> >> +       select DEFAULT_UIMAGE
>> >> >>         help
>> >> >>           This option enables support for the IBM PPC440EP evaluation board.
>> >> >
>> >> > Who knows what the actual bamboo board used. But I'd be happy to take a
>> >> > SOB'ed patch to do the above, because these days the qemu emulation is
>> >> > much more likely to be used than the actual board.
>> >>
>> >> I just went to see why my CI boot of 44x didn't catch this, and it's
>> >> because I don't use the uImage, I just boot the vmlinux directly:
>> >>
>> >>   $ qemu-system-ppc -M bamboo -m 128m -display none -kernel build~/vmlinux -append "console=ttyS0" -display none -nodefaults -serial mon:stdio
>> >>   Linux version 5.8.0-rc1-00118-g69119673bd50 (michael@...ine1-p1) (gcc (Ubuntu 9.3.0-10ubuntu2) 9.3.0, GNU ld (GNU Binutils for Ubuntu) 2.34) #4 Wed Jun 17 20:19:22 AEST 2020
>> >>   Using PowerPC 44x Platform machine description
>> >>   ioremap() called early from find_legacy_serial_ports+0x690/0x770. Use early_ioremap() instead
>> >>   printk: bootconsole [udbg0] enabled
>> >>
>> >>
>> >> So that's probably the simplest solution?
>> >
>> > If the uImage or zImage self decompresses, I would prefer to test that as well.
>> 
>> The uImage is decompressed by qemu AIUI.
>> 
>> >> That means previously arch/powerpc/boot/zImage was just a hardlink to
>> >> the uImage:
>> >
>> > It sounds like we can just boot the zImage, or is that no longer
>> > created with the uImage?
>> 
>> The zImage won't boot on bamboo.
>> 
>> Because of the vagaries of the arch/powerpc/boot/Makefile the zImage
>> ends up pointing to treeImage.ebony, which is for a different board.
>> 
>> The zImage link is made to the first item in $(image-y):
>> 
>> $(obj)/zImage:		$(addprefix $(obj)/, $(image-y))
>> 	$(Q)rm -f $@; ln $< $@
>>                          ^
>>                          first preqrequisite
>> 
>> Which for this defconfig happens to be:
>> 
>> image-$(CONFIG_EBONY)			+= treeImage.ebony cuImage.ebony
>> 
>> If you turned off CONFIG_EBONY then the zImage will be a link to
>> treeImage.bamboo, but qemu can't boot that either.
>> 
>> It's kind of nuts that the zImage points to some arbitrary image
>> depending on what's configured and the order of things in the Makefile.
>> But I'm not sure how we make it less nuts without risking breaking
>> people's existing setups.
>
> Hi Michael,
>
> For what it's worth, this is squared this away in terms of our CI by
> just building and booting the uImage directly, rather than implicitly
> using the zImage:
>
> https://github.com/ClangBuiltLinux/continuous-integration/pull/282
> https://github.com/ClangBuiltLinux/boot-utils/pull/22

Great.

> We were only using the zImage because that is what Joel Stanley intially
> set us up with when PowerPC 32-bit was added to our CI:
>
> https://github.com/ClangBuiltLinux/continuous-integration/pull/100

Ah, so Joel owes us all beers then ;)

> Admittedly, we really do not have many PowerPC experts in our
> organization so we are supporting it on a "best effort" basis, which
> often involves using whatever knowledge is floating around or can be
> gained from interactions such as this :) so thank you for that!

No worries. I definitely don't expect you folks to invest much effort in
powerpc, especially the old 32-bit stuff, so always happy to help debug
things, and really appreciate the testing you do.

cheers