Re: [PATCH 1/1] coresight: fix issue where coresight component has no claimtags

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

Hi Mike,

On Wed, Oct 22, 2025 at 01:35:46PM +0100, Mike Leach wrote:

[...]

> > - We can add a new flag ("bool claim_impl" in the struct csdev_access),
> >   by default the field will be zero.
> >
> 
> I considered a bool - but the correct place for this would be
> coresight_device - where we keep all the information about the
> hardware features.

Maybe coresight_device is suitable. But this might require to update
furthermore for claim function arguments (e.g., need to pass "csdev"
rather than "csdev_access").

> > - The drivers support claim tags call coresight_clear_self_claim_tag()
> >   in probe (see __catu_probe() as an example), we can call a new
> >   function coresight_init_claim_tag() to replace it, this function sets
> >   "claim_impl" properly and clear the tag if supported.
> >
> 
> I considered moving this initialisation to the common coresight code
> where we create the coresight_device.

Seems to me, this is dangerous. If a module is not CoreSight compliant
and claim registers are absent, when access we will get unknown values
or even cause serious result (external abort or bus lockup).

[...]

> > > +/*
> > > + * Coresight specification defines a maximum of 8 claim tag bits.
> > > + * The precise number is implementation defined, and may be obtained by
> > > + * reading the CLAIMSET register.
> > > + */
> > > +#define CORESIGHT_CLAIM_BITS_MAX_MASK        GENMASK(7, 0)
> > > +#define CORESIGHT_CLAIM_SELF_HOSTED_BIT      BIT(1)
> >
> > Now we only care about the self-host bit. Can reuse existed macros ?
> >
> 
> I feel that drivers should be written to match the specification - the
> macros above are a correct mask value per specification and the
> correct bitfield comparison for the MSBit of the protocol.
> 
> The ones below are a protocol masks field, and a specific protocol
> value that is used in value rather than bit comparisons in the
> claimtag code. I felt it clearer to differentiate between the uses
> when reading the code.

How about change CORESIGHT_CLAIM_EXTERNAL and
CORESIGHT_CLAIM_SELF_HOSTED to MSBit ?

Thanks,
Leo