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

[Nicolas Pitre]

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