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

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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@xxxxxxx




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

Suzuki




Best regards,
Krzysztof







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