linux-kernel - Re: [PATCH v3 5/6] phy: qcom: qmp-combo: register a typec mux to change the QMPPHY

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Message-ID: <7f464eb7-469c-4350-a43a-3b99394ad689@oss.qualcomm.com>
Date: Wed, 28 May 2025 00:22:01 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Konrad Dybcio <konradybcio@...nel.org>
Cc: 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>,
        Bjorn Andersson <andersson@...nel.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Neil Armstrong <neil.armstrong@...aro.org>
Subject: Re: [PATCH v3 5/6] phy: qcom: qmp-combo: register a typec mux to
 change the QMPPHY_MODE

On 5/27/25 11:55 PM, Dmitry Baryshkov wrote:
> On Tue, May 27, 2025 at 10:40:07PM +0200, Konrad Dybcio wrote:
>> From: Neil Armstrong <neil.armstrong@...aro.org>
>>
>> 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.
>>
>> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
>> [konrad: renaming, rewording, bug fixes]
>> Signed-off-by: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
>> ---

[...]

>> +	} else {
>> +		/* Fall back to USB3+DP mode if we're not sure it's strictly USB3-only */
> 
> Why? if the SID is not DP, then there can't be a DP stream.
> 
>> +		if (state->mode == TYPEC_MODE_USB3 || state->mode == TYPEC_STATE_USB)
>> +			new_mode = QMPPHY_MODE_USB3_ONLY;
>> +		else
>> +			new_mode = QMPPHY_MODE_USB3DP;

To be honest I don't really know.. Neil chose to do that, but I don't
think there's a strict requirement.. Should we default to 4ln-USB3?

[...]

> Consider the following scenario: connect DP dongle, use modetest to
> setup DP stream, disconnect dongle, connect USB3 device. What would be
> the actual state of the PHY? Modetest is still running, so DP stream is
> not going to be shut down from the driver.
> 
> I think we might need a generic notifier from the PHY to the user,
> telling that the PHY is going away (or just that the PHY is changing the
> state). Then it would be usable by both the DP and USB drivers to let
> them know that they should toggle the state.


If modetest won't stop running even though there was a DP unplug
(and therefore presumably a destruction of the display), I don't
think things are designed very well

Konrad