Message-ID: <75dde9a2-3c0d-481b-bc73-089ba89a77e0@linaro.org>
Date: Mon, 2 Jun 2025 10:55:58 +0200
From: Neil Armstrong <neil.armstrong@...aro.org>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
 Dmitry Baryshkov <dmitry.baryshkov@....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,
 Krzysztof Kozlowski <krzk@...nel.org>
Subject: Re: [PATCH v3 0/6] arm64: qcom: allow up to 4 lanes for the Type-C
 DisplayPort Altmode

On 28/05/2025 18:56, Konrad Dybcio wrote:
> On 5/28/25 1:22 PM, Dmitry Baryshkov wrote:
>> On Wed, May 28, 2025 at 01:13:26PM +0200, Konrad Dybcio wrote:
>>> On 5/28/25 11:00 AM, Dmitry Baryshkov wrote:
>>>> On Wed, May 28, 2025 at 12:24:02AM +0200, Konrad Dybcio wrote:
>>>>> On 5/27/25 11:10 PM, Dmitry Baryshkov wrote:
>>>>>> On Tue, May 27, 2025 at 10:40:02PM +0200, Konrad Dybcio 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.
>>>>>>
>>>>>> This series doesn't seem to solve the USB side of a problem. When the
>>>>>> PHY is being switch to the 4-lane mode, USB controller looses PIPE
>>>>>> clock, so it needs to be switched to the USB-2 mode.
>>>>>
>>>>> I didn't find issues with that on X13s.. Not sure if it's related, but
>>>>> on the SL7, after plugging in a 4ln DP connection, I need to plug in
>>>>> the USB thumb drive twice for the first time (only in that sequence)
>>>>
>>>> Might be.
>>>>
>>>>> But there's nothing interesting in dmesg and the phy seems to be
>>>>> programmed with the same values on both the initial and the subsequent
>>>>> working plug-in
>>>>
>>>> Please try using a DP dongle with USB 2 passthrough (there are some).
>>>> Or just emulate this by enabling DP PHY / DP chain for plugged in USB3
>>>> devices. Would you be able to see the USB device on a bus?
>>>
>>> I only have a dongle with both display and usb that does 2ln dp
>>> (I tested 4ln dp on a type-c display that I don't think has a hub)
>>>
>>> USB3 - yes, USB2 - no (but it works after a replug)
>>>
>>> Are you talking about essentially doing qcom,select-utmi-as-pipe-clk
>>> at runtime?
>>
>> I think so.
> 
> So after quite some time playing with that, I noticed that the USB2
> device was never actually kicked off the bus.. and works totally fine
> after connecting the display output (2ln DP)
> 
> I was looking at dmesg, checking for discovery/disconnect messages,
> but the device was simply never disconnected (which makes sense given
> repurposing USB3 TX/RX lanes doesn't affect the D+/D- of USB2)
> 
> I also read some docs and learnt that what we call
> qcom,select-utmi-as-pipe-clk is suppossed to be a debug feature
> and is unnecessary to set on USB2.0-only controllers
> 
> The USB controller programming guide though doesn't talk about DP,
> but I'd expect that we may need to set that override for 4lnDP+USB2
> use cases (which I don't have a dongle for)

Yeah basically we need to:
1) power-off the USB3 PHY
2) switch to UTMI clock

In the following states:
- USB safe mode (USB2 lanes may still be connected)
- 4lanes DP mode
- DP-only mode

But for this, the dwc3 should also get USB-C events with an addition mode-switch property.
The flatten DWC3 node now allows that !

Neil

> 
> Konrad

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