Re: [PATCH v6 01/19] coresight: sysfs: Validate CPU online status for per-CPU sources

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

On Fri, Mar 13, 2026 at 11:03:02AM +0000, Suzuki K Poulose wrote:
> On 05/03/2026 10:17, Leo Yan wrote:
> > The current SysFS flow first enables the links and sink, then rolls back
> > to disable them if the source fails to enable. This failure can occur if
> > the associated CPU is offline, which causes the SMP call to fail.
> > 
> > Populate CPU ID into the coresight_device structure, for components that
> > are not CPU bound, set this field to -1.
> > 
> > Validate whether the associated CPU is online for a per-CPU tracer. If
> > the CPU is offline, return -ENODEV and bail out.
> > 
> > Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
> > Reviewed-by: Mike Leach <mike.leach@linaro.org>
> > Tested-by: James Clark <james.clark@linaro.org>
> > Signed-off-by: Leo Yan <leo.yan@arm.com>
> 
> While this works, how about we make it an explicit buy in from the driver
> for CPU bound ?
> 
> e.g., add a flag in the coresight_desc.flags = CORESIGHT_DESC_CPU_BOUND
> 
> and then desc.cpu describes the associated CPU. Otherwise, defaults to -1.
> That way you could restrict the changes to only those that need the
> CPU (ETMx and CTIs ?) Also makes any new driver safe.

Instead of adding a flag, I'd use a helper to check existed flags:

  static inline bool coresight_is_cpu_bound(struct coresight_device *csdev)
  {
         if (!csdev)
                 return false;

         if (coresight_is_percpu_source(csdev))
                 return true;

         if (csdev->type == CORESIGHT_DEV_TYPE_HELPER &&
             csdev->subtype.helper_subtype == CORESIGHT_DEV_SUBTYPE_HELPER_ECT_CTI)
                 return true;

         return false;
  }

Only CPU bound device will assign CPU ID, otherwise will set -1.

Thanks,
Leo