Re: [PATCH 08/13] coresight: Add support for CLAIM tag protocol

[Suzuki K Poulose]

On 15/08/18 00:20, Mathieu Poirier wrote:
> On Mon, Aug 06, 2018 at 02:41:50PM +0100, Suzuki K Poulose wrote:
> > Add support for the CLAIM tag protocol for negotiating the
> > device ownership with other agents trying to use the coresight
> > component (internal vs. external). The Coresight architecture
> > specifies CLAIM tags (managed via CLAIMSET CLAIMCLR registers)
> > to negotiate the ownership of the device. PSCI recommends the
> > reservation of the bits in CLAIM tags for self-hosted and external
> > debug use. This patch implements the protocol for claiming
> > the devices before they are actually used.
>
> I think the first paragraph of the cover letter (minus the reference to the
> documentation since you've included it below) would be perfect instead of the
> above.
>
> > Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > ---
> >   drivers/hwtracing/coresight/coresight-priv.h |  7 +++
> >   drivers/hwtracing/coresight/coresight.c      | 85 ++++++++++++++++++++++++++++
> >   include/linux/coresight.h                    | 20 +++++++
> >   3 files changed, 112 insertions(+)

> > +void coresight_disclaim_device_unlocked(void __iomem *base)
> > +{
> > +
> > +	if (coresight_is_claimed_self_hosted(base))
> > +		coresight_clear_claim_tags(base);
> > +	else
> > +		/*
> > +		 * Either we or the external agent doesn't follow
> > +		 * the protocol.
> > +		 */
> > +		WARN_ON_ONCE(1);
>
> When writing "... or the external agent doesn't follow the protocol", I deduce
> that an external agent would have trampled our claim tag.  I think this needs
> to be said explicitly in the comment.

> > +static inline int coresight_claim_device_unlocked(void __iomem *base)
> > +{
> > +	return 0;
> > +}
> > +
> > +static inline int coresight_claim_device(void __iomem *base)
> > +{
> > +	return 0;
> > +}
>
> Returning 0 would give a caller the impression the operation has succeeded when
> in fact it didn't.  I think we should return an error code here.


Agreed on all points, will respin.

Suzuki