[PATCH] coresight: etm4x: Fix timestamp bit field handling

[James Clark]

On 19/05/2025 2:50 pm, Leo Yan wrote:
> Timestamps in the trace data appear as all zeros on recent kernels,
> although the feature works correctly on old kernels (e.g., v6.12).
> 
> Since commit c382ee674c8b ("arm64/sysreg/tools: Move TRFCR definitions
> to sysreg"), the TRFCR_ELx_TS_{VIRTUAL|GUEST_PHYSICAL|PHYSICAL} macros
> were updated to remove the bit shift. As a result, the driver no longer
> shifts bits when operates the timestamp field.
> 
> Fix this by using the FIELD_PREP() and FIELD_GET() helpers. Simplify the
> ts_source_show() function: return -1 when the value is zero, as this
> indciates an invalid value; otherwise return the decoded TS value
> directly.
> 
> Reported-by: Tamas Zsoldos <tamas.zsoldos at arm.com>
> Fixes: c382ee674c8b ("arm64/sysreg/tools: Move TRFCR definitions to sysreg")
> Signed-off-by: Leo Yan <leo.yan at arm.com>
> ---
>   .../hwtracing/coresight/coresight-etm4x-core.c  |  2 +-
>   .../hwtracing/coresight/coresight-etm4x-sysfs.c | 17 ++---------------
>   2 files changed, 3 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index 6a5898355a83..acb4a58e4bb9 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -1237,7 +1237,7 @@ static void cpu_detect_trace_filtering(struct etmv4_drvdata *drvdata)
>   	 * tracing at the kernel EL and EL0, forcing to use the
>   	 * virtual time as the timestamp.
>   	 */
> -	trfcr = (TRFCR_EL1_TS_VIRTUAL |
> +	trfcr = (FIELD_PREP(TRFCR_EL1_TS_MASK, TRFCR_EL1_TS_VIRTUAL) |
>   		 TRFCR_EL1_ExTRE |
>   		 TRFCR_EL1_E0TRE);
>   
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> index 49d5fb87a74b..8a2749eeb9a5 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> @@ -2315,23 +2315,10 @@ static ssize_t ts_source_show(struct device *dev,
>   	int val;
>   	struct etmv4_drvdata *drvdata = dev_get_drvdata(dev->parent);
>   
> -	if (!drvdata->trfcr) {
> +	val = FIELD_GET(TRFCR_EL1_TS_MASK, drvdata->trfcr);
> +	if (!val)
>   		val = -1;
> -		goto out;
> -	}
> -
> -	switch (drvdata->trfcr & TRFCR_EL1_TS_MASK) {
> -	case TRFCR_EL1_TS_VIRTUAL:
> -	case TRFCR_EL1_TS_GUEST_PHYSICAL:
> -	case TRFCR_EL1_TS_PHYSICAL:
> -		val = FIELD_GET(TRFCR_EL1_TS_MASK, drvdata->trfcr);
> -		break;
> -	default:
> -		val = -1;
> -		break;
> -	}
>   
> -out:
>   	return sysfs_emit(buf, "%d\n", val);
>   }
>   static DEVICE_ATTR_RO(ts_source);

Reviewed-by: James Clark <james.clark at linaro.org>