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

Rob Herring robherring2 at gmail.com
Mon Oct 8 22:27:31 EDT 2012

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 should fix things.



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:
                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

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