kernel decompressor problem for ARMv7

Lin Ming
2013-07-08T02:27:15Z

On Sat, 2013-07-06 at 00:58 +0800, Lin Ming wrote:
> On Sat, Jul 6, 2013 at 12:30 AM, Nicolas Pitre <nicolas.pitre@linaro.org> wrote:
> > On Fri, 5 Jul 2013, Will Deacon wrote:
> >
> >> On Fri, Jul 05, 2013 at 09:44:12AM +0100, Lin Ming wrote:
> >> > Hi all,
> >>
> >> Hello,
> >>
> >> > I'm porting BSP code from v2.6.36 to v3.10 kernel. It's ARMv7 processor.
> >>
> >> Which specific processor/SoC?
> >>
> >> > But decompressor doesn't work. With a lot of debug, I finally find
> >> > below 2 commits related.
> >> > Kernel uncompress OK with these commits reverted.
> >> >
> >> > dbece45: ARM: 7501/1: decompressor: reset ttbcr for VMSA ARMv7 cores
> >> > (Introduced in v3.6-rc6)
> >> >
> >> > 5010192: ARM: 7583/1: decompressor: Enable unaligned memory access for
> >> > v6 and above
> >> > (Introduced in v3.7-rc8)
> >> >
> >> > Any hint to fix it?
> >>
> >> There's not really enough information to go on here. What specifically
> >> fails? Also, do you have to revert *both* of the above changes to get things
> >> working again?
> >
> > Also, what is the bootloader used here?
>
> uboot.
>
> >
> > Does the bootloader call the kernel with the MMU off as documented in
> > Documentation/arm/Booting?
>
> How to check this?
>
> I'll check uboot code or add debug code in boot/compressed/head.S to
> check it next Monday.

I added below debug code to print the control reg from lowest 4bits to
highest 4bits.

It prints "B7805C". So the control reg is 0x00c5087b.
Seems bootloader calls the kernel with MMU enabled and Alignment fault
checking enabled.

diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index 32337ff..9434720 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -125,6 +125,23 @@
.rept 7
mov r0, r0
.endr
+
+ /* Dirty debug code to print control reg from lowest 4bits to highest 4bits */
+ ldr r2, =0xf0070120 @ UART
+ mrc p15, 0, r0, c1, c0, 0 @ read control reg
+ 1:
+ cmp r0, #0
+ beq 2f
+ and r1, r0, #15
+ cmp r1, #9
+ addgt r1, r1, #7
+ add r1, r1, #48
+ str r1, [r2]
+ asr r0, r0, #4
+ b 1b
+ 2:
+
+
ARM( mov r0, r0 )
ARM( b 1f )
THUMB( adr r12, BSYM(1f) )

>
> >
> > Nicolas