Re: [PATCH v2 3/4] coresight: etm4x: Report the external outputs the PMU counts

[Leo Yan]

On Mon, Oct 12, 2026 at 04:05:22PM -0700, Amir Ayupov wrote:

[...]

> --- a/drivers/hwtracing/coresight/coresight-config.h
> +++ b/drivers/hwtracing/coresight/coresight-config.h
> @@ -35,6 +35,10 @@
>   * a device that matches one of its classes and has all of its capabilities.
>   */
>  #define CS_CFG_MATCH_CAP_MASK		0x0000ff00
> +/* trace unit external output n is countable by the PMU as TRCEXTOUTn */
> +#define CS_CFG_MATCH_CAP_PMU_EXTOUT_SHIFT	8
> +#define CS_CFG_MATCH_CAP_PMU_EXTOUT_NR	4	/* TRCEXTOUT0-3 */
> +#define CS_CFG_MATCH_CAP_PMU_EXTOUT(n)	BIT(CS_CFG_MATCH_CAP_PMU_EXTOUT_SHIFT + (n))

We can just use a single capacity for all output singals. It would be
good to follow the naming convention in the Arm ARM:

  #define CS_CFG_MATCH_CAP_TRCEXTOUT            BIT(8)

>  int etm4_cscfg_register(struct coresight_device *csdev)
>  {
> +	struct etmv4_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>  	struct cscfg_csdev_feat_ops ops;
> +	u32 match_flags = CS_CFG_ETM4_MATCH_FLAGS;
>  
>  	ops.load_feat = &etm4_cfg_load_feature;
> +	match_flags |= (u32)drvdata->pmu_extout << CS_CFG_MATCH_CAP_PMU_EXTOUT_SHIFT;
>  
> -	return cscfg_register_csdev(csdev, CS_CFG_ETM4_MATCH_FLAGS, &ops);
> +	return cscfg_register_csdev(csdev, match_flags, &ops);

I would suggest to enable the capability bit base on drvdata->caps:

  if (etm4x_is_ete(drvdata) && drvdata->caps.nr_events)
	match_flags |= CS_CFG_MATCH_CAP_TRCEXTOUT;

For now, we can enable TRCEXTOUT for ETE only, as this should be
sufficient to detect the feature safely. I'd like to leave this to
James and Mike as I got suggestions from them.

Please also rebase onto the latest CoreSight next branch [1], which
moves the capability fields into drvdata->caps. I found an issue in the
decoding of caps.nr_event; the attached patch fixes it and makes the
field hold the actual event count.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/coresight/linux.git branch: next

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