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

[andrzej zaborowski]

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
> > CPU_INTERRUPT_DEBUG).
> >
> > >  - 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.

Andrzej

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