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

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Date:   Thu, 18 Jun 2020 10:48:21 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Michal Simek <michal.simek@...inx.com>,
        Nathan Chancellor <natechancellor@...il.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

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.

cheers