Re: [PATCH] perf/arm-cmn: Fix {wp_dev_sel2, wp_dev_sel} limited to 0/1 when MXP_MULTIPLE_DTM_EN is TRUE

[Robin Murphy]

On 19/08/2026 11:54 am, 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.
>
> 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 applying `dev %= 2` to clamp the selection value to
> the valid range when MXP_MULTIPLE_DTM_EN is TRUE.
>
> Fixes: 60d1504070c2 ("perf/arm-cmn: Support new IP features")
> Signed-off-by: Shouping Wang <allen.wang@xxxxxxxxxxxx>
> ---
>   drivers/perf/arm-cmn.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c
> index 40c05c519a1d..13ccbf2a7345 100644
> --- a/drivers/perf/arm-cmn.c
> +++ b/drivers/perf/arm-cmn.c
> @@ -1392,6 +1392,7 @@ 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);

Nit: may as well refactor the is_cmn600 condition to reference cmn->part 
directly too.

>   	u32 config;
>   	u32 dev = CMN_EVENT_WP_DEV_SEL(event);
>   	u32 chn = CMN_EVENT_WP_CHN_SEL(event);
> @@ -1404,6 +1405,9 @@ static u32 arm_cmn_wp_config(struct perf_event *event, int wp_idx)
>   	if (is_cmn600)
>   		grp &= 1;
>   
> +	if (cmn->multi_dtm)
> +		dev %=  2;
> +

Let's just make the whole setting of CMN_DTM_WPn_CONFIG_WP_DEV_SEL2 
conditional on !multi_dtm, like for exclusive and combine further down 
(note that the CMN-600 "grp &= 1" is different, since that's more about 
sanitising invalid input values rather than the register encoding itself.)

Thanks,
Robin.

>   	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) |