Re: [PATCH v2] perf/arm-cmn: Fix wp_dev_sel2 setting for multi-DTM configurations

[Robin Murphy]

On 10/09/2026 12:46 pm, Shouping Wang wrote:
> When MXP_MULTIPLE_DTM_EN is TRUE, each DTM will monitor at most
> two device ports. In this case, {wp_dev_sel2, wp_dev_sel} will
> only use values 2'b00 and 2'b01 per DTM.

Poor documentation strikes again!

> Previously the setting allowed values beyond the supported range
> per DTM, which could cause each DTM to select invalid ports when
> MXP_MULTIPLE_DTM_EN is TRUE.
>
> Fix this by only setting CMN_DTM_WPn_CONFIG_WP_DEV_SEL2 when
> !multi_dtm.

Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>

Thanks for the fix!
Robin.

> Fixes: 60d1504070c2 ("perf/arm-cmn: Support new IP features")
> Signed-off-by: Shouping Wang <allen.wang@xxxxxxxxxxxx>
> ---
>
> Changes in v2:
> - Made the setting of CMN_DTM_WPn_CONFIG_WP_DEV_SEL2 conditional on
>    !multi_dtm, instead of clamping with dev %= 2.
> - Refactored is_cmn600 to use cmn->part directly.
> - Updated the commit message.
>
> Link to v1: https://lore.kernel.org/lkml/20260819105443.668784-1-allen.wang@xxxxxxxxxxxx/
>
>   drivers/perf/arm-cmn.c | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c
> index 6e5cc4086a9e..7e7590381171 100644
> --- a/drivers/perf/arm-cmn.c
> +++ b/drivers/perf/arm-cmn.c
> @@ -1393,13 +1393,14 @@ static void arm_cmn_claim_wp_idx(struct arm_cmn_dtm *dtm,
>   
>   static u32 arm_cmn_wp_config(struct perf_event *event, int wp_idx)
>   {
> +	struct arm_cmn *cmn = to_cmn(event->pmu);
>   	u32 config;
>   	u32 dev = CMN_EVENT_WP_DEV_SEL(event);
>   	u32 chn = CMN_EVENT_WP_CHN_SEL(event);
>   	u32 grp = CMN_EVENT_WP_GRP(event);
>   	u32 exc = CMN_EVENT_WP_EXCLUSIVE(event);
>   	u32 combine = CMN_EVENT_WP_COMBINE(event);
> -	bool is_cmn600 = to_cmn(event->pmu)->part == PART_CMN600;
> +	bool is_cmn600 = cmn->part == PART_CMN600;
>   
>   	/* CMN-600 supports only primary and secondary matching groups */
>   	if (is_cmn600)
> @@ -1407,8 +1408,11 @@ static u32 arm_cmn_wp_config(struct perf_event *event, int wp_idx)
>   
>   	config = FIELD_PREP(CMN_DTM_WPn_CONFIG_WP_DEV_SEL, dev) |
>   		 FIELD_PREP(CMN_DTM_WPn_CONFIG_WP_CHN_SEL, chn) |
> -		 FIELD_PREP(CMN_DTM_WPn_CONFIG_WP_GRP, grp) |
> -		 FIELD_PREP(CMN_DTM_WPn_CONFIG_WP_DEV_SEL2, dev >> 1);
> +		 FIELD_PREP(CMN_DTM_WPn_CONFIG_WP_GRP, grp);
> +
> +	if (!cmn->multi_dtm)
> +		config |= FIELD_PREP(CMN_DTM_WPn_CONFIG_WP_DEV_SEL2, dev >> 1);
> +
>   	if (exc)
>   		config |= is_cmn600 ? CMN600_WPn_CONFIG_WP_EXCLUSIVE :
>   				      CMN_DTM_WPn_CONFIG_WP_EXCLUSIVE;