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

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

[Shouping Wang]

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@hj-micro.com>
---
 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);
 	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;
+
 	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) |
-- 
2.43.0

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

[allen.wang]

Hi,

Gentle ping on this patch.

Could someone please review it when time permits?

Thanks!
Allen

On 8/19/2026 6:54 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.
> 
> 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@hj-micro.com>
> ---
>  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);
>  	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;
> +
>  	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) |

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 08/09/2026 9:15 am, allen.wang wrote:
> Hi,
> 
> Gentle ping on this patch.
> 
> Could someone please review it when time permits?
> 
> Thanks!
> Allen
> 
> On 8/19/2026 6:54 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.

Hmm, I read the "each DTM will only use..." wording[1] as implying that 
the hardware itself would ignore wp_dev_sel2 (especially since that 
would seem to be the obvious thing to do) - are you saying that that 
isn't the case? (I've never had access to any actual multi-DTM hardware...)

Thanks,
Robin.

[1] 
https://support.arm.com/documentation/102308/0307/Debug-trace-and-PMU/Debug-Trace-system-overview/DTM-watchpoint?lang=en

>> 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@hj-micro.com>
>> ---
>>   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);
>>   	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;
>> +
>>   	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) |
> 

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

[allen.wang]

Hi Robin:

Yes, that's exactly what I'm saying. I've tested this on actual
multi-DTM hardware, and the hardware does not ignore wp_dev_sel2
automatically — it must be correctly configured by software.

Thanks!
Allen

On 9/8/2026 11:04 PM, Robin Murphy wrote:
> https://support.arm.com/documentation/102308/0307/Debug-trace-and-PMU/
> Debug-Trace-system-overview/DTM-watchpoint?lang=en

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@hj-micro.com>
> ---
>   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) |

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

[Shouping Wang]

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 only setting CMN_DTM_WPn_CONFIG_WP_DEV_SEL2 when
!multi_dtm.

Fixes: 60d1504070c2 ("perf/arm-cmn: Support new IP features")
Signed-off-by: Shouping Wang <allen.wang@hj-micro.com>
---

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@hj-micro.com/

 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;
-- 
2.43.0

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@arm.com>

Thanks for the fix!
Robin.

> Fixes: 60d1504070c2 ("perf/arm-cmn: Support new IP features")
> Signed-off-by: Shouping Wang <allen.wang@hj-micro.com>
> ---
> 
> 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@hj-micro.com/
> 
>   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;

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

[Will Deacon]

On Thu, 10 Sep 2026 19:46:01 +0800, 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.
> 
> [...]

Applied to arm64 (for-next/fixes), thanks!

[1/1] perf/arm-cmn: Fix wp_dev_sel2 setting for multi-DTM configurations
      https://git.kernel.org/arm64/c/49daa3d668b6

Cheers,
-- 
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev