linux-kernel - Re: [PATCH RFT 4/7] phy: qcom: qmp-combo: register a typec mux to change the QPHY

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Date: Thu, 29 Feb 2024 16:57:43 +0100
From: neil.armstrong@...aro.org
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konrad.dybcio@...aro.org>, Vinod Koul <vkoul@...nel.org>,
 Kishon Vijay Abraham I <kishon@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, linux-arm-msm@...r.kernel.org,
 linux-phy@...ts.infradead.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFT 4/7] phy: qcom: qmp-combo: register a typec mux to
 change the QPHY_MODE

On 29/02/2024 16:54, Dmitry Baryshkov wrote:
> On Thu, 29 Feb 2024 at 17:47, Neil Armstrong <neil.armstrong@...aro.org> wrote:
>>
>> On 29/02/2024 16:25, Dmitry Baryshkov wrote:
>>> On Thu, 29 Feb 2024 at 15:08, Neil Armstrong <neil.armstrong@...aro.org> wrote:
>>>>
>>>> Register a typec mux in order to change the PHY mode on the Type-C
>>>> mux events depending on the mode and the svid when in Altmode setup.
>>>>
>>>> The DisplayPort phy should be left enabled if is still powered on
>>>> by the DRM DisplayPort controller, so bail out until the DisplayPort
>>>> PHY is not powered off.
>>>>
>>>> The Type-C Mode/SVID only changes on plug/unplug, and USB SAFE states
>>>> will be set in between of USB-Only, Combo and DisplayPort Only so
>>>> this will leave enough time to the DRM DisplayPort controller to
>>>> turn of the DisplayPort PHY.
>>>
>>> I think this is not fully correct. Please correct me if I'm wrong, but
>>> it is possible to switch between USB / USB+DP / DP-only at runtime.
>>> See the Status Update and Configure commands.
>>
>> Yes, but the current implementation is still valid because we need to
>> have the DP powered-off before changing the PHY mode.
> 
> Even for switching between 2 lane and 4 lane modes?

So the Altmode pin assignment says how much lanes you can get (2 or 4),
and AUX data will say how much the adapter/display supports.

My native DP monitor uses the 4 lanes, while my USB-C->HDMI dongles
declares the 4lanes pin assigment but DP controller only ever tries 2 lanes.

I don't have USB-C->HDMI with 4lanes DP, but it should work fine.

Neil

> 
> I'll check how my USB-A+DP dongles work with respect to the altmode
> configuration.
> 
>>
>> I never encountered such setup and I have no idea how to test this.
>>
>>>
>>>>
>>>> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
> 
>