Re: [PATCH v4 04/13] coresight: Hide unused ETMv3 format attributes

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

On Wed, Nov 12, 2025 at 03:22:10PM +0000, James Clark wrote:
> ETMv3 only has a few attributes, and setting unused ones results in an
> error, so hide them to begin with.
> 
> Signed-off-by: James Clark <james.clark@linaro.org>
> ---
>  drivers/hwtracing/coresight/coresight-etm-perf.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> index 17afa0f4cdee..91132abca244 100644
> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> @@ -106,8 +106,27 @@ static struct attribute *etm_config_formats_attr[] = {
>  	NULL,
>  };
>  
> +static umode_t etm_format_attr_is_visible(struct kobject *kobj,
> +					  struct attribute *attr, int unused)
> +{
> +	/* ETM4 has all attributes */
> +	if (IS_ENABLED(CONFIG_CORESIGHT_SOURCE_ETM4X))
> +		return attr->mode;
> +
> +	/* ETM3 only has these attributes */
> +	if (attr == &format_attr_cycacc.attr ||
> +	    attr == &format_attr_timestamp.attr ||
> +	    attr == &format_attr_retstack.attr ||
> +	    attr == &format_attr_sinkid.attr ||
> +	    attr == &format_attr_configid.attr)

Do we support configid for ETM3?

> +		return attr->mode;

It is good to give a bit information why only these attributes
supported, e.g.,

  /*
   * ETM3 only support subset attributes (see ETM3X_SUPPORTED_OPTIONS),
   * keep 'sinkid' attr for specifying sink ID.
   */

Two side topics but not issues caused this patch:

- Since CTXTID/CTXTID2 is only used for ETM4x, we can remove "#if
  IS_ENABLED(CONFIG_CORESIGHT_SOURCE_ETM4X)" from the
  format_attr_contextid_show() function.

- etm_parse_event_config() does not check attr->config3, thus user
  sets 'cc_threshold' it will slip without any error report.

Thanks,
Leo

> +
> +	return 0;
> +}
> +
>  static const struct attribute_group etm_pmu_format_group = {
>  	.name   = "format",
> +	.is_visible = etm_format_attr_is_visible,
>  	.attrs  = etm_config_formats_attr,
>  };
>  
> 
> -- 
> 2.34.1
>