linux-kernel - Re: [PATCH 0/3] phy: qcom: edp: Add support for DT phy mode configuration

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Message-ID: <0ba94f0f-3df5-4eaf-a88c-c63aebff4232@linaro.org>
Date: Thu, 25 Jan 2024 17:36:06 +0100
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Abel Vesa <abel.vesa@...aro.org>
Cc: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
 Vinod Koul <vkoul@...nel.org>, Kishon Vijay Abraham I <kishon@...nel.org>,
 Bjorn Andersson <andersson@...nel.org>, Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Johan Hovold <johan@...nel.org>,
 linux-phy@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 0/3] phy: qcom: edp: Add support for DT phy mode
 configuration



On 1/15/24 10:52, Abel Vesa wrote:
> On 24-01-03 14:42:49, Konrad Dybcio wrote:
>> On 21.12.2023 17:27, Dmitry Baryshkov wrote:
>>> On Tue, 19 Dec 2023 at 22:55, Abel Vesa <abel.vesa@...aro.org> wrote:
>>>>
>>>> Until now, all platform that supported both eDP and DP had different
>>>> compatibles for each mode. Using different compatibles for basically
>>>> the same IP block but for a different configuration is bad way all
>>>> around. There is a new compute platform from Qualcomm that supports
>>>> both eDP and DP with the same PHY. So instead of following the old
>>>> method, we should allow the mode to be configured from devicetree.
>>>>
>>>> There has been an off-list discussion on what would be the right way
>>>> to pass on the PHY mode information to the driver and it has been
>>>> concluded that phy-cells is the way to go. This means that basically
>>>> the controller will pass another value (that is, the PHY type) to
>>>> its 'phys' DT property.
>>>>
>>>> For this, we need both the bindings value and the PHY mode value to be
>>>> added as well.
>>>>
>>>> The controller part will follow shortly. But for now, lets see where
>>>> this is going.
>>>>
>>>> There has been another attempt at this here:
>>>> https://lore.kernel.org/all/20231122-phy-qualcomm-edp-x1e80100-v3-3-576fc4e9559d@linaro.org/
>>>>
>>>> Compared to that version, this one uses the phy-cells method and drops
>>>> the X1E80100 support. The X1E80100 support will be a separate patchset.
>>>
>>> After several back and forth discussions, I think that this approach
>>> is not correct and not that easy to extend. Instead I'd like to
>>> suggest adding a property to the DP controller, which enables eDP
>>> behaviour (and thus makes DP driver call phy_set_mode()). Something
>>> like this:
>>> dp: displayport-controller@...000 {
>>>      compatible = "qcom,sm8000-dp";
>>>      /* reg, interrupts, etc */
>>>     edp-interface;
>>>     /* or simpler */
>>>     is-edp;
>>> };
>>>
>>> What do you think?
>>
>> Please excuse my alzheimer, but why did we not go with phy-type after
>> the last discussion?
> 
> phy-type would be a property of the phy. That way we would need pass
> the mode to the controller. So it was concluded that passing that
> information from the controller via phy_set_mode is more straightforward.

Eeh, reluctantly, I'm gonna say yes. It's not the prettiest solution,
but none of the ones I can think of seem much better.

Konrad