Re: [PATCH v5 6/9] coresight: add support for CPU debug module

[Suzuki K Poulose]

On 29/03/17 11:27, Leo Yan wrote:
> On Wed, Mar 29, 2017 at 10:07:07AM +0100, Suzuki K Poulose wrote:
>
> [...]
>
> > > > > +	if (mode == EDDEVID_IMPL_NONE) {
> > > > > +		drvdata->edpcsr_present  = false;
> > > > > +		drvdata->edcidsr_present = false;
> > > > > +		drvdata->edvidsr_present = false;
> > > > > +	} else if (mode == EDDEVID_IMPL_EDPCSR) {
> > > > > +		drvdata->edpcsr_present  = true;
> > > > > +		drvdata->edcidsr_present = false;
> > > > > +		drvdata->edvidsr_present = false;
> > > > > +	} else if (mode == EDDEVID_IMPL_EDPCSR_EDCIDSR) {
> > > > > +		if (!IS_ENABLED(CONFIG_64BIT) &&
> > > > > +			(pcsr_offset == EDDEVID1_PCSR_NO_OFFSET_DIS_AARCH32))
> > > > > +			drvdata->edpcsr_present = false;
> > > > > +		else
> > > > > +			drvdata->edpcsr_present = true;
> > > >
> > > > Sorry, I forgot why we do this check only in this mode. Shouldn't this be
> > > > common to all modes (of course which implies PCSR is present) ?
> > >
> > > No. PCSROffset is defined differently in ARMv7 and ARMv8; So finally we
> > > simplize PCSROffset value :
> > > 0000 - Sample offset applies based on the instruction state (indicated by PCSR[0])
> > > 0001 - No offset applies.
> > > 0010 - No offset applies, but do not use in AArch32 mode!
> > >
> > > So we need handle the corner case is when CPU runs AArch32 mode and
> > > PCSRoffset = 'b0010. Other cases the pcsr should be present.
> >
> > I understand that reasoning. But my question is, why do we check for PCSROffset
> > only when mode == EDDEVID_IMPL_EDPCSR_EDCIDSR and not for say mode == EDDEVID_IMPL_EDPCSR or
> > any other mode where PCSR is present.
>
> Sorry I misunderstood your question.
>
> I made mistake when I analyzed the possbile combination for mode and
> PCSROffset so I thought it's the only case should handle:
> { EDDEVID_IMPL_EDPCSR_EDCIDSR, EDDEVID1_PCSR_NO_OFFSET_DIS_AARCH32 }
>
> Below three combinations are possible to exist; so you are right, I
> should move this out for the checking:
> { EDDEVID_IMPL_NONE,           EDDEVID1_PCSR_NO_OFFSET_DIS_AARCH32 }

That need not be covered, as IMPL_NONE says PCSR is not implemented hence you
don't worry about anything as the functionality is missing. This should rather be:
EDDEVID_IMPL_EDPCSR, where only PCSR is implemented.

My switch...case suggestion makes it easier to do all this checking.


Thanks
Suzuki