linux-kernel - Re: [RFC PATCH 2/6] dt-bindings: net: wireless: ath12k: describe WSI property for QCN9274

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Message-ID: <808cfb83-a80f-431c-be69-ee3da964482a@kernel.org>
Date: Wed, 23 Oct 2024 19:57:43 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Raj Kumar Bhagat <quic_rajkbhag@...cinc.com>, ath12k@...ts.infradead.org
Cc: linux-wireless@...r.kernel.org, Kalle Valo <kvalo@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Jeff Johnson <jjohnson@...nel.org>,
 Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [RFC PATCH 2/6] dt-bindings: net: wireless: ath12k: describe WSI
 property for QCN9274

On 23/10/2024 14:22, Raj Kumar Bhagat wrote:
> 
> The above three blocks represent the QCN9274 WiFi devices connected to their
> respective PCI slots. The dotted line represents the WSI connection that connects
> these three devices together. Hence, the WSI interface is part of the QCN9274 device.
> 
> To describe this WSI hardware connection in the device tree, we are adding three
> properties inside the WSI object:
> 
> 1. qcom,wsi-group-id:
>    In the above diagram, we have one WSI connection connecting all three devices.
>    Hence, “qcom,wsi-group-id” for all three devices can be 0.
> 
>    This cannot be implied by the compatible property, as explained below:
>    Let’s take the case of a platform that can have four QCN9274 WiFi devices. Below
>    is one possibility of a WSI connection:
> 
>          +-------+       +-------+          +-------+      +-------+
>          | pcie2 |       | pcie3 |          | pcie1 |      | pcie0 |
>          |       |       |       |          |       |      |       |
>    +---->|  wsi  |------>|  wsi  |--+   +-->|  wsi  |----->|  wsi  |----+
>    |     | idx 0 |       | idx 1 |  |   |   | idx 0 |      | idx 1 |    |
>    |     +-------+       +-------+  |   |   +-------+      +-------+    |
>    +--------------------------------+   +-------------------------------+
> 
>    In this case, QCN9274 devices connected in PCIe2 and PCIe3 will have the same
>    “qcom,wsi-group-id”. This group-id will be different from the “qcom,wsi-group-id”
>    of QCN9274 devices connected at PCIe1 and PCIe0.

Thanks, this explains why group-id cannot be same...

> 
> 2. qcom,wsi-index:
>    This is a unique identifier of the device within the same group. The value of
>    wsi-idx is represented in both the above cases (RDP433 and the 4 WiFi device
>    platform) in the diagram itself.

But still any device-indexing is in general not accepted (and was
mentioned during reviews multiple times).

This looks like circular list, so phandle will be enough. You only need
to mark devices being part of the same chain.

Actually graph with endpoints would be more suitable, assuming above
diagram represents connections.

Please include that diagram in binding description.

> 
> 3. qcom,wsi-num-devices:
>    Represents the number of devices connected through WSI within the same WSI group to
>    which the device belongs.
>    
>    In the case of RDP433, all devices will have this number as 3.
>    For the second example with four WiFi devices but with two WSI connections, the
>    value of “qcom,wsi-num-devices” for each device will be 2.

Not needed, just iterate over the graph children.

Best regards,
Krzysztof