linux-kernel - Re: [PATCH RFT 0/7] arm64: qcom: allow up to 4 lanes for the Type-C DisplayPort Altmode

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Date: Sat, 16 Mar 2024 11:01:25 -0500
From: Bjorn Andersson <andersson@...nel.org>
To: Neil Armstrong <neil.armstrong@...aro.org>
Cc: Luca Weiss <luca.weiss@...rphone.com>, 
	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>, 
	Abhinav Kumar <quic_abhinavk@...cinc.com>, linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFT 0/7] arm64: qcom: allow up to 4 lanes for the Type-C
 DisplayPort Altmode

On Fri, Mar 15, 2024 at 06:35:15PM +0100, Neil Armstrong wrote:
> On 15/03/2024 18:19, Luca Weiss wrote:
> > On Thu Feb 29, 2024 at 2:07 PM CET, Neil Armstrong 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.
> > > 
> > > The patchset also includes bindings changes and DT changes.
> > > 
> > > This has been successfully tested on an SM8550 board, but the
> > > Thinkpad X13s deserved testing between non-PD USB, non-PD DisplayPort,
> > > PD USB Hubs and PD Altmode Dongles to make sure the switch works
> > > as expected.
> > > 
> > > The DisplayPort 4 lanes setup can be check with:
> > > $ cat /sys/kernel/debug/dri/ae01000.display-controller/DP-1/dp_debug
> > > 	name = msm_dp
> > > 	drm_dp_link
> > > 		rate = 540000
> > > 		num_lanes = 4
> > 
> > Hi Neil,
> > 
> > I tried this on QCM6490/SC7280 which should also support 4-lane DP but I
> > haven't had any success so far.
> > 
[..]
> > [ 1775.563969] [drm:dp_ctrl_link_train] *ERROR* max v_level reached
> > [ 1775.564031] [drm:dp_ctrl_link_train] *ERROR* link training #1 failed. ret=-11
> 
> Interesting #1 means the 4 lanes are not physically connected to the other side,
> perhaps QCM6490/SC7280 requires a specific way to enable the 4 lanes in the PHY,
> or some fixups in the init tables.
> 

I tested the same on rb3gen2 (qcs6490) a couple of weeks ago, with the
same outcome. Looking at the AUX reads, after switching to 4-lane the
link training is failing on all 4 lanes, in contrast to succeeding only
on the first 2 if you e.g. forget to mux the other two.

As such, my expectation is that there's something wrong in the QMP PHY
(or possibly redriver) for this platform.

Regards,
Bjorn