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: <4a6066ed-ead4-4387-8c66-b3e7631c5e90@arm.com>
Date: Wed, 9 Oct 2024 11:52:22 +0100
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Tao Zhang <quic_taozha@...cinc.com>, Mike Leach <mike.leach@...aro.org>,
 James Clark <james.clark@....com>, 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

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 ?

Suzuki


> 
> 
> 
>>
>> Happy to proceed with anything that seems acceptable for you folks.
>>
>> Suzuki
>>
>>
>>
>>>
>>> Best regards,
>>> Krzysztof
>>>
>>
>