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: <8692f79f-142c-43e6-9e09-7ed4ce590b87@oss.qualcomm.com>
Date: Wed, 28 May 2025 13:21:40 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Konrad Dybcio <konradybcio@...nel.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>,
        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,
        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 5/28/25 10:58 AM, Dmitry Baryshkov wrote:
> On Wed, May 28, 2025 at 12:22:01AM +0200, Konrad Dybcio wrote:
>> 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?
> 
> Yes, QMPPHY_MODE_USB3_ONLY. Nit: there is no 4ln-USB3 (it is a special
> mode). We handle 2ln-USB3 only.

Right, I double checked and we support SS

> 
>>
>> [...]
>>
>>> 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
> 
> They are, but differently. Display settings are always controlled by
> DRM clients (typically, a userspace compositor). They can decide to
> send data to unconnected display, they can decide to ignore HPD events,
> etc. Even if userspace responds to the event, there always will be some
> delay. I choose modetest, because it's a particularly good example of a
> delay going to the infinity.

0_o

Konrad