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Re: [Qemu-devel] [PATCH] PXA-specific ARM hacks.

From: andrzej zaborowski
Subject: Re: [Qemu-devel] [PATCH] PXA-specific ARM hacks.
Date: Sat, 17 Mar 2007 21:16:23 +0100

On 17/03/07, andrzej zaborowski <address@hidden> wrote:
On 17/03/07, Paul Brook <address@hidden> wrote:
> On Friday 16 March 2007 22:06, andrzej zaborowski wrote:
> > This patch contains some ugly but very useful chnages:
> >  - in cpu-exec.c, halt the arm CPU on CPU_INTERRUPT_HALT like in other
> > architectures.
> This is ok. Though I'd prefer it to actually be common code (like
> >  - wake the cpu up on CPU_INTERRUPT_EXITTB - this serves waking the
> > CPU up without asserting IRQ or FIQ, which is possible on PXA. Would
> > it be better to add a separate interrupt type instead?
> I think this is probably ok. Could do with a comment somewhere saying so.
> >  - in target-arm/translate.c, don't terminate the TB after a CP15
> > write. The purpose of this is to imitate the real processor's
> > instruction cache (to some degree). OSes should never need rely on the
> > cache prefetch but unfortunately Linux for pxa does when it's waking
> > up from sleep or deep idle, when enabling the MMU (simplifies things a
> > lot for Linux).
> This is not acceptable in its current form. IIRC on arm cores the effects take
> effect once all insn have worked through the pipeline (typically a few
> cycles), and I bet there's code that relies on this. ie:
> mcr cp15, ...;nop;nop;nop;nop;@expect cp15 write to have taken effect by now
> A more acceptable solution would be:
> - Only extend the TB for the specific instruction that linux abuses
> - Limit the number of instructions that can follow before the end of the TB.
> - Add a comment saying what this hack is for.

Ok. Attaching a second version of this patch. The number of
instructions after MMU enable and before TB ends is limited by the
obligatory CPWAIT rather than in qemu.

Oops, one more try. This time removing the use of cpu_reset() on
entering Standby because cpu_reset() now does more than we want.


Attachment: 0015-PXA-specific-ARM-hacks.txt
Description: Text document

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