Re: [PATCH] ARC: guard dsp early init against non ARCv2

From: Eugeniy Paltsev
Date: Wed Apr 29 2020 - 13:12:59 EST


Hi Vineet,

> From: Vineet Gupta <vgupta@xxxxxxxxxxxx>
> Sent: Tuesday, April 28, 2020 22:46
> To: Eugeniy Paltsev; linux-snps-arc@xxxxxxxxxxxxxxxxxxx
> Cc: Alexey Brodkin; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH] ARC: guard dsp early init against non ARCv2
>
> On 4/28/20 11:50 AM, Eugeniy Paltsev wrote:
> > As of today we guard early DSP init code with
> > ARC_AUX_DSP_BUILD (0x7A) BCR check to verify that we have
> > CPU with DSP configured. However that's not enough as in
> > ARCv1 CPU the same BCR (0x7A) is used for checking MUL/MAC
> > instructions presence.
> >
> > So, let's guard DSP early init against non ARCv2.
> >
> > Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@xxxxxxxxxxxx>
> > ---
> > arch/arc/include/asm/dsp-impl.h | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/arch/arc/include/asm/dsp-impl.h b/arch/arc/include/asm/dsp-impl.h
> > index e1aa212ca6eb..e64d945ae7df 100644
> > --- a/arch/arc/include/asm/dsp-impl.h
> > +++ b/arch/arc/include/asm/dsp-impl.h
> > @@ -15,12 +15,14 @@
> >
> > /* clobbers r5 register */
> > .macro DSP_EARLY_INIT
> > +#if defined(CONFIG_ISA_ARCV2)
>
> ifdef is the canonical way for a single macro to check.
>
> Also, this needs to be finer grained, i.e. CONFIG_ARC_DSP_KERNEL which is already
> tied to ARCV2 only configs.

We shouldn't limit the scope of this code part [dsp early init] to the cases
were DSP support is enabled in kconfig - and that is the reason why this code
initially was guarded with BCR check only.

So, I change the check to

#if defined(CONFIG_ARC_DSP_HANDLED) || defined(CONFIG_ARC_DSP_NONE)

which is actually the equivalent to

#if defined(CONFIG_ISA_ARCV2)

but I don't think it's worth thing to do.

>
> > lr r5, [ARC_AUX_DSP_BUILD]
> > bmsk r5, r5, 7
> > breq r5, 0, 1f
> > mov r5, DSP_CTRL_DISABLED_ALL
> > sr r5, [ARC_AUX_DSP_CTRL]
> > 1:
> > +#endif
> > .endm
> >
> > /* clobbers r10, r11 registers pair */

---
Eugeniy Paltsev