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: <D064242SMIVM.1GUC1I9GE9IGC@fairphone.com>
Date: Fri, 29 Mar 2024 10:02:39 +0100
From: "Luca Weiss" <luca.weiss@...rphone.com>
To: "Konrad Dybcio" <konrad.dybcio@...aro.org>, "Bjorn Andersson"
 <andersson@...nel.org>, "Neil Armstrong" <neil.armstrong@...aro.org>
Cc: "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 Tue Mar 26, 2024 at 10:02 PM CET, Konrad Dybcio wrote:
> On 16.03.2024 5:01 PM, 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.
> > 
> > As such, my expectation is that there's something wrong in the QMP PHY
> > (or possibly redriver) for this platform.
>
> Do we have any downstream tag where 4lane dp works? I'm willing to believe
> the PHY story..

Just tested on Fairphone 5 downstream and 4 lane appears to work there.
This is with an USB-C to HDMI adapter that only does HDMI.

FP5:/ # cat /sys/kernel/debug/drm_dp/dp_debug
        state=0x20a5
        link_rate=270000
        num_lanes=4
        resolution=2560x1440@...z
        pclock=241500KHz
        bpp=24
        test_req=DP_LINK_STATUS_UPDATED
        lane_count=4
        bw_code=10
        v_level=0
        p_level=0

Sources are here:
https://gerrit-public.fairphone.software/plugins/gitiles/kernel/msm-5.4/+/refs/heads/odm/rc/target/13/fp5
And probably more importantly techpack/display:
https://gerrit-public.fairphone.software/plugins/gitiles/platform/vendor/opensource/display-drivers/+/refs/heads/odm/rc/target/13/fp5
Dts if useful:
https://gerrit-public.fairphone.software/plugins/gitiles/kernel/msm-extra/devicetree/+/refs/heads/kernel/13/fp5

Regards
Luca

>
> Konrad