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

On 10/08/2012 11:01 PM, Nicolas Pitre wrote:

On Mon, 8 Oct 2012, Rob Herring wrote:

quoted

On 10/08/2012 06:28 PM, Shawn Guo wrote:

quoted

On Mon, Oct 08, 2012 at 03:34:57PM -0500, Rob Herring wrote:

quoted

On 10/08/2012 11:43 AM, Shawn Guo wrote:

quoted

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.

quoted

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.

quoted

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.

It is still optional on v6 and the compiler will not emit unaligned
accesses for v6 (which is why it worked when v6 platforms were enabled).
That does raise a bigger question. If we're doing combined v6 and v7
builds, do we want this to require unaligned accesses are enabled and if
so, can we force that on in the compiler?

Rob