Re: [PATCH v6 2/2] coresight: cti: Add Qualcomm extended CTI support

[Leo Yan <leo.yan@arm.com>]

On Thu, Dec 04, 2025 at 09:15:07AM +0000, Mike Leach wrote:

[...]

> > > +             /*
> > > +              * QCOM CTI does not implement Claimtag functionality as
> > > +              * per CoreSight specification, but its CLAIMSET register
> > > +              * is incorrectly initialized to 0xF. This can mislead
> > > +              * tools or drivers into thinking the component is claimed.
> > > +              *
> > > +              * Reset CLAIMSET to 0 to reflect that no claims are active.
> > > +              */
> > > +             writel_relaxed(0, drvdata->base + CORESIGHT_CLAIMSET);
> >
> > I am confused for this.  If QCOM CTI does not implement claim tag,
> > then what is the designed register at the offset CORESIGHT_CLAIMSET?
> >
> > Should you bypass all claim tag related operations for QCOM CTI case?
> > (I don't see you touch anything for claim and declaim tags).
> >
> 
> The patch I have created to handle systems without correct claim tag
> operation is a dependency for this patch set. Thus no need for
> override here as the core code will handle this correctly.
> 
> The only issue is ensuring the non-CTI spec implementation will result
> in the correct detection of no claim tags present.

Your patch works only when a module has implemented claim registers.

This leads to two issues: we end up clearing an unknown register in the
CTI driver, and then the coresight core layer assumes it is reading a
claim register even though it is not.

For QCOM CTI, combined with your patch, I would suggest directly
setting csdev->access.claim_tag_impl to false (perhaps using a helper).
This would be much clearer than the "hacking" way.

Thanks,
Leo