[PATCH] ARM: head: Remove boot-time HYP mode check for v5 and below

[dave.martin@linaro.org (Dave Martin)]

On Mon, Dec 10, 2012 at 06:39:55PM +0100, Marko Kati? wrote:
> On Mon, Dec 10, 2012 at 11:57 AM, Dave Martin <dave.martin@linaro.org> wrote:
> > Hi Russell,
> >
> > Do you want me to send this patch to the patch system?
> >
> > Until we have confirmation from Marko (or someone else with a board)
> > there's no way to know whether it fixes the problem.  But it should
> > restore us back to the old behaviour older hardware, reducing the
> > likelihood of side issues.
> >
> > This could be reverted later if it proves to be unnecessary.
> >
> > Cheers
> > ---Dave
> >
> > On Fri, Dec 07, 2012 at 01:45:59PM +0000, Dave Martin wrote:
> >> The kernel can only be entered on HYP mode on CPUs which actually
> >> support it, i.e.  >= ARMv7.  pre-v6 platform support cannot coexist
> >> in the same kernel as support for v7 and higher, so there is no
> >> advantage in having the HYP mode check on pre-v6 hardware.
> >>
> >> At least one pre-v6 board is known to fail when the HYP mode check
> >> code is present, although the exact cause remains unknown and may
> >> be unrelated.  [1]
> >>
> >> This patch restores the old behaviour for pre-v6 platforms, whereby
> >> the CPSR is forced directly to SVC mode with IRQs and FIQs masked.
> >> All kernels capable of booting on v7 hardware will retain the
> >> check, so this should not impair functionality.
> >>
> >> [1] http://lists.arm.linux.org.uk/lurker/message/20121130.013814.19218413.en.html
> >> ([ARM] head.S change broke platform device registration?)
> >>
> >> Signed-off-by: Dave Martin <dave.martin@linaro.org>
> >> ---
> >>  arch/arm/include/asm/assembler.h |    8 ++++++++
> >>  1 files changed, 8 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
> >> index 2ef9581..eb87200 100644
> >> --- a/arch/arm/include/asm/assembler.h
> >> +++ b/arch/arm/include/asm/assembler.h
> >> @@ -250,6 +250,7 @@
> >>   * Beware, it also clobers LR.
> >>   */
> >>  .macro safe_svcmode_maskall reg:req
> >> +#if __LINUX_ARM_ARCH__ >= 6
> >>       mrs     \reg , cpsr
> >>       mov     lr , \reg
> >>       and     lr , lr , #MODE_MASK
> >> @@ -266,6 +267,13 @@ THUMB(   orr     \reg , \reg , #PSR_T_BIT        )
> >>       __ERET
> >>  1:   msr     cpsr_c, \reg
> >>  2:
> >> +#else
> >> +/*
> >> + * workaround for possibly broken pre-v6 hardware
> >> + * (akita, Sharp Zaurus C-1000, PXA270-based)
> >> + */
> >> +     setmode PSR_F_BIT | PSR_I_BIT | SVC_MODE, \reg
> >> +#endif
> >>  .endm
> >>
> >>  /*
> >> --
> >> 1.7.4.1
> >>
> 
> I confirm that this patch fixes the regression on Akita machines
> introduced with commit:
> 
> 424e5994e63326a42012f003f1174f3c363c7b62
> ARM: zImage/virt: hyp mode entry support for the zImage loader
> 
> The abovementioned commit breaks Zaurus machine ID detection code
> (arm/boot/compressed/head-sharpsl.S)
> causing Akita machines to boot with the wrong machine ID.

Thanks for testing.  I've now posted the patch to the patch system.

> Just a minor nitpick:
> s/clobers/clobbers/g

Good spot, but I'll leave the patch unchanged for now.

This typo is in the existing code, not part of the fix.
I'll try to tidy this up if I touch this code again.

Cheers
---Dave