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

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Message-ID: <ce439616-072b-463f-b293-8a186f8282bd@kernel.org>
Date: Fri, 18 Oct 2024 12:05:20 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Tao Zhang <quic_taozha@...cinc.com>,
 Suzuki K Poulose <suzuki.poulose@....com>
Cc: Mike Leach <mike.leach@...aro.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Mathieu Poirier <mathieu.poirier@...aro.org>,
 Leo Yan <leo.yan@...ux.dev>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
 linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v3 1/3] dt-bindings: arm:
 qcom,coresight-static-replicator: Add property for source filtering

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.

Best regards,
Krzysztof