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

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Message-Id: <CZWTD7P4CE12.1ZUNPF2WFTBHR@fairphone.com>
Date: Mon, 18 Mar 2024 11:45:57 +0100
From: "Luca Weiss" <luca.weiss@...rphone.com>
To: "Bjorn Andersson" <andersson@...nel.org>, "Neil Armstrong"
 <neil.armstrong@...aro.org>
Cc: "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 Sat Mar 16, 2024 at 5:01 PM CET, Bjorn Andersson wrote:
> 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.

Good to know it's not just my device then ;)

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

Since I imagine rb3gen2 uses a different redriver setup compared to FP5,
I wouldn't say that's at fault for now? And at least my ptn36502 driver
only has very little difference between 2-lane and 4-lane setup, only
setting the mode to DP-only and 4-lane (vs USB+DP and 2-lane), nothing
else.

Regards
Luca

>
> Regards,
> Bjorn