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: <44e2617c-62b0-436f-ac6a-0bd3e3855473@arm.com>
Date: Thu, 22 Aug 2024 11:34:36 +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

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.

Happy to proceed with anything that seems acceptable for you folks.

Suzuki



> 
> Best regards,
> Krzysztof
>