[PATCH] perf/arm-cmn: Move overlapping wp_combine field

[Ilkka Koskinen]

Hi Robin,

On Wed, 1 Mar 2023, Ilkka Koskinen wrote:
>
> Hi Robin,
>
> On Wed, 1 Mar 2023, Robin Murphy wrote:
>> On 2023-03-01 17:55, Ilkka Koskinen wrote:
>>> As eventid field was expanded to support new mesh versions, it started to
>>> overlap with wp_combine field. Move wp_combine to fix the issue.
>> 
>> Watchpoint events still only strictly need 2 bits of eventid, though. Could 
>> you clarify whether userspace is getting confused by this, or whether it's 
>> just arm_cmn_event_init() falling over itself (FWIW I can see how I broke 
>> things there...)
>
> Basically, perf seems to set eventid at first and then wp_combine field into 
> the config argument. The problem is when arm_cmn_event_init() is doing:
>
> 	eventid = CMN_EVENT_EVENTID(event);
> 	....
> 	if (eventid != CMN_WP_UP && eventid != CMN_WP_DOWN)
> 		return -EINVAL;
>
> If wp_combine has any of the overlapping bits set, eventid doesn't match with 
> either up or down event.

I probably should have also copy pasted what the format files say:

 	$ cat format/eventid format/wp_combine
 	config:16-26
 	config:24-27

So, here you can see that those two fields overlap. If wp_combine has any 
of the bits 24-26 set, arm_cmn_event_init() returns -EINVAL as shown in 
the code above.

Would you need some more clarification from me?

Br, Ilkka


>
> Cheers, Ilkka
>
>> 
>> Thanks,
>> Robin.
>> 
>>> Fixes: 23760a014417 ("perf/arm-cmn: Add CMN-700 support")
>>> Signed-off-by: Ilkka Koskinen <ilkka at os.amperecomputing.com>
>>> ---
>>>   drivers/perf/arm-cmn.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>> 
>>> diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c
>>> index c9689861be3f..9f2edc28d16e 100644
>>> --- a/drivers/perf/arm-cmn.c
>>> +++ b/drivers/perf/arm-cmn.c
>>> @@ -166,7 +166,7 @@
>>>   #define CMN_EVENT_BYNODEID(event)	FIELD_GET(CMN_CONFIG_BYNODEID, 
>>> (event)->attr.config)
>>>   #define CMN_EVENT_NODEID(event)		FIELD_GET(CMN_CONFIG_NODEID, 
>>> (event)->attr.config)
>>>   -#define CMN_CONFIG_WP_COMBINE		GENMASK_ULL(27, 24)
>>> +#define CMN_CONFIG_WP_COMBINE		GENMASK_ULL(30, 27)
>>>   #define CMN_CONFIG_WP_DEV_SEL		GENMASK_ULL(50, 48)
>>>   #define CMN_CONFIG_WP_CHN_SEL		GENMASK_ULL(55, 51)
>>>   /* Note that we don't yet support the tertiary match group on newer IPs 
>>> */
>> 
>