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

[Suzuki K Poulose]

On 16/03/2026 14:02, Leo Yan wrote:
> 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 at arm.com>
>>> Reviewed-by: Mike Leach <mike.leach at linaro.org>
>>> Tested-by: James Clark <james.clark at linaro.org>
>>> Signed-off-by: Leo Yan <leo.yan at 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)

That works, but if a new device type comes in, we may have to expand the
list. Having a flag makes much more sense and the core driver only does
what has been asked for. I prefer the flags.

Cheers
Suzuki



>                   return true;
> 
>           return false;
>    }
> 
> Only CPU bound device will assign CPU ID, otherwise will set -1.
> 
> Thanks,
> Leo