linux-kernel - Re: [PATCH 2/2] phy: qcom-mipi-csi2: Add a CSI2 MIPI D-PHY driver

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Message-ID: <427548c0-b0e3-4462-a15e-bd7843f00c7f@oss.qualcomm.com>
Date: Tue, 15 Jul 2025 11:33:00 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Vladimir Zapolskiy <vladimir.zapolskiy@...aro.org>,
        Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        Vinod Koul
 <vkoul@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>
Cc: Bryan O'Donoghue <bod@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-phy@...ts.infradead.org, linux-media@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] phy: qcom-mipi-csi2: Add a CSI2 MIPI D-PHY driver

On 7/15/25 11:20 AM, Vladimir Zapolskiy wrote:
> On 7/15/25 12:01, Konrad Dybcio wrote:
>> On 7/15/25 8:35 AM, Vladimir Zapolskiy wrote:
>>> On 7/15/25 03:13, Bryan O'Donoghue wrote:
>>>> On 14/07/2025 16:30, Vladimir Zapolskiy wrote:
>>>>>>
>>>>>> I think that is genuinely something we should handle in camss-csid.c
>>>>>> maybe with some meta-data inside of the ports/endpoints..
>>>>>>
>>>>>
>>>>> This is a CSIPHY property, a CSIPHY hardware configuration and a wiring
>>>>> of sensors to a CSIPHY. Where is the relation to CSID here? There is no.
>>>>
>>>> All the PHY really needs to know is the # of lanes in aggregate, which
>>>> physical lanes to map to which logical lanes and the pixel clock.
>>>>
>>>> We should add additional support to the Kernel's D-PHY API parameters
>>>> mechanism to support that physical-to-logical mapping but, that's not
>>>> required for this series or for any currently know upstream user of CAMSS.
>>>>
>>>>> Please share at least a device tree node description, which supports
>>>>> a connection of two sensors to a single CSIPHY, like it shall be done
>>>>> expectedly.
>>>> &camss {
>>>>        port@0 {
>>>>            csiphy0_lanes01_ep: endpoint0 {
>>>>                data-lanes = <0 1>;
>>>>                remote-endpoint = <&sensor0_ep>;
>>>>            };
>>>>
>>>>            csiphy0_lanes23_ep: endpoint0 {
>>>>                data-lanes = <2 3>;
>>>>                remote-endpoint = <&sensor1_ep>;
>>>>            };
>>>>         };
>>>> };
>>>
>>> Don't you understand that this is broken?.. That's no good.
>>>
>>> Please listen and reread the messages given to you above, your proposed
>>> "solution" does not support by design a valid hardware setup of two
>>> sensors connected to the same CSIPHY.
>>>
>>> I would propose to stop force pushing an uncorrectable dt scheme, it
>>> makes no sense.
>>
>> If all you're asking for is an ability to grab an of_graph reference
>> from the camss (v4l2) driver, you can simply do something along the
>> lines of of_graph_get_remote_port(phy->dev->of_node)
>>
> 
> It's not about the driver specifics, my comment is about a proper
> hardware description in dts notation, please see the device tree node
> names.

I'm a little lost on what you're trying to argue for..

I could make out:

1. "the phy should be a multimedia device"
2. "There is no ports at all, which makes the device tree node unusable,
  since you can not provide a way to connect any sensors to the phy."

I don't really understand #1.. maybe that could be the case if the PHY
has a multitude of tunables (which I don't know if it does, but wouldn't
be exactly surprised if it did) that may be usecase/pipeline-specific

As for #2, I do think it makes sense to connect the sensors to the PHY,
as that's a representation of electrical signals travelling from the
producer to the consumer (plus the data passed in e.g. data-lanes is
directly related to the PHY and necessarily consumed by its driver)

Konrad