[PATCH v2 3/5] ARM: use generic unaligned.h

Nicolas Pitre
2012-10-09T04:01:05Z

On Mon, 8 Oct 2012, Rob Herring wrote:

> On 10/08/2012 06:28 PM, Shawn Guo wrote:
> > On Mon, Oct 08, 2012 at 03:34:57PM -0500, Rob Herring wrote:
> >> On 10/08/2012 11:43 AM, Shawn Guo wrote:
> >>> This patch has been merged into mainline as commit below.
> >>>
> >>> d25c881 ARM: 7493/1: use generic unaligned.h
> >>>
> >>> It introduces a regression for me. Check out the commit on mainline,
> >>> build a v7 only kernel (imx5/6) with imx_v6_v7_defconfig, the kernel
> >>> halts in decompressor. But v6/v7 kernel (imx3/5/6) works fine. The
> >>> kernel built on the parent commit below works all fine.
> >>
> >> It actually fails in the decompressor or that's the last output you get?
> >
> > I think it fails in the decompressor, because what I see is
> >
> > Uncompressing Linux...
> >
> > not
> >
> > Uncompressing Linux... done, booting the kernel.
> >
> >> I compared the decompressor disassembly of both cases and get the same
> >> number of ldrb/strb instructions, so I don't think it is directly
> >> related to alignment.
> >>
> >> I tried the XY decompressor as that is one difference, but that works
> >> fine for me on highbank.
> >>
> >> Does it work with an empty uncompress.h functions? That should be the
> >> only difference in our decompressor code.
> >
> > No, empty putc() in uncompress.h does not help.
> >
> > New finding is that it only fails with LZO decompressor while the other
> > 3 Gzip, LZMA and XZ all work good. We happen to have LZO as the default
> > one in imx_v6_v7_defconfig.
>
> I must have had an old config with XZ. LZO fails because of this:
>
> lib/decompress_unlzo.c: version = get_unaligned_be16(parse);
> lib/decompress_unlzo.c: if (get_unaligned_be32(parse) & HEADER_HAS_FILTER)
> lib/decompress_unlzo.c: dst_len = get_unaligned_be32(in_buf);
> lib/decompress_unlzo.c: src_len = get_unaligned_be32(in_buf);
>
> This was what I was afraid of. The decompressor runs with the sysctrl
> register A bit in whatever state the bootloader left it in. In the case
> of u-boot it is set, and the maintainers are pretty set on not allowing
> unaligned accesses if you've seen the recent discussion.

This is not an u-Boot issue. The kernel code expects misaligned
accesses to be handled by the hardware on ARMv6+ now. So it better
enforce proper A bit state itself.

> This should fix things.
>
> Rob
>
> 8<---------------------------------------------------------------------
>
> diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
> index bc67cbf..1f87d22 100644
> --- a/arch/arm/boot/compressed/head.S
> +++ b/arch/arm/boot/compressed/head.S
> @@ -654,6 +654,7 @@ __armv7_mmu_cache_on:
> #endif
> mrc p15, 0, r0, c1, c0, 0 @ read control reg
> bic r0, r0, #1 << 28 @ clear SCTLR.TRE
> + bic r0, r0, #1 << 1 @ clear SCTLR.A
> orr r0, r0, #0x5000 @ I-cache enable, RR cache replacement
> orr r0, r0, #0x003c @ write buffer
> #ifdef CONFIG_MMU
>

That's OK for ARMv7, but in the ARMv6 case we use __armv4_mmu_cache_on.
So this patch is incomplete.

Nicolas