Re: [PATCH v3 1/3] dt-bindings: arm: qcom,coresight-static-replicator: Add property for source filtering

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 18/10/2024 11:05, Krzysztof Kozlowski wrote:
> On 17/10/2024 09:23, Tao Zhang wrote:
>>
>> On 10/9/2024 6:52 PM, Suzuki K Poulose wrote:
>>> Krzysztof
>>>
>>> On 22/08/2024 12:50, Suzuki K Poulose wrote:
>>>> On 22/08/2024 11:34, Suzuki K Poulose wrote:
>>>>> On 22/08/2024 08:08, Krzysztof Kozlowski wrote:
>>>>>> On Wed, Aug 21, 2024 at 11:38:55AM +0100, Suzuki K Poulose wrote:
>>>>>>> On 21/08/2024 04:13, Tao Zhang wrote:
>>>>>>>> The is some "magic" hard coded filtering in the replicators,
>>>>>>>> which only passes through trace from a particular "source". Add
>>>>>>>> a new property "filter-src" to label a phandle to the coresight
>>>>>>>> trace source device matching the hard coded filtering for the port.
>>>>>>>
>>>>>>> Minor nit: Please do not use abbreviate "source" in the bindings.
>>>>>>> I am not an expert on other changes below and will leave it to
>>>>>>> Rob/Krzysztof to comment.
>>>>>>>
>>>>>>> Rob, Krzysztof,
>>>>>>>
>>>>>>> We need someway to "link" (add a phandle) from a "port". The patch
>>>>>>> below
>>>>>>> is extending "standard" port to add a phandle. Please let us know if
>>>>>>> there is a better way.
>>>>>>>
>>>>>>> e.g.:
>>>>>>>
>>>>>>> filters = list of tuples of port, phandle. ?
>>>>>>>
>>>>>>> e.g.:
>>>>>>>
>>>>>>> filters = < 0, <&tpdm_video>,
>>>>>>>               1, <&tpdm_mdss>
>>>>>>>         >
>>>>>>>
>>>>>>
>>>>>> Current solution feels like band-aid - what if next time you need some
>>>>>> second filter? Or "wall"? Or whatever? Next property?
>>>>>
>>>>>
>>>>>
>>>>>>
>>>>>> Isn't filter just one endpoint in the graph?
>>>>>>
>>>>>> A <--> filter <--> B
>>>>>
>>>>> To be more precise, "Filter" is a "port (p0, p1, p2 below)" (among a
>>>>> multi output ports).
>>>>>
>>>>> For clearer example:
>>>>>
>>>>> A0 <--> .. <--> ..\                  p0  / --> Filtered for (A1)
>>>>> <--> B1
>>>>> A1 <--> .. <--> .. - < L(filters>    p1  - --> Filtered for (A2)
>>>>> <--> B2
>>>>> A2 <--> .. <--> ../                  p2  \ --> Unfiltered
>>>>> <--> B0
>>>>>
>>>>>
>>>>>
>>>>>> Instead of
>>>>>>
>>>>>> A <----through-filter----> B?
>>>>>
>>>>> The problem is we need to know the components in the path from A0 to X
>>>>> through, (Not just A0 and L). And also we need to know "which port
>>>>> (p0 vs p1 vs p2)" does the traffic take from a source (A0/A1/A2) out
>>>>> of the
>>>>> link "L".
>>>>>
>>>>> So ideally, we need a way to tie p0 -> A1, p1 -> A2.
>>>>>
>>>>> would we need something else in the future ? I don't know for sure.
>>>>> People could design their own things ;-). But this was the first time
>>>>> ever in the last 12yrs since we supported coresight in the kernel.
>>>>> (there is always a first time).
>>>>>
>>>>> Fundamentally, the "ports" cannot have additional properties today.
>>>>> Not sure if there are other usecases (I don't see why). So, we have
>>>>> to manually extend like above, which I think is not nice.
>>>>
>>>> Replying to the other thread [0], made me realize that the above is not
>>>> true. Indeed it is possible to add properties for endpoints, e.g:
>>>>
>>>> e.g.: media/video-interfaces.yaml
>>>>
>>>> So extending the endpoint node is indeed acceptable (unlike I thought).
>>>> May be the we it is achieved in this patch is making it look otherwise.
>>>>
>>>> Suzuki
>>>> [0]
>>>> https://lkml.kernel.org/r/4b51d5a9-3706-4630-83c1-01b01354d9a4@arm.com
>>>
>>> Please could you let us know if it is acceptable to extend "endpoint"
>>> node to have an optional property ?
>>
>> Hi Krzysztof,
>>
>>
>> Kindly reminder, could you help comment on this?
> 
> I don't have any smart ideas and with earlier explanation sounds ok.

Just to confirm, are you OK with adding a property to the "endpoint"
node that will indicate a phandle that the device allows on this
endpoint ?

Kind regards
Suzuki


> 
> Best regards,
> Krzysztof
>