linux-kernel - Re: [PATCH v6 0/8] drm/tidss: Use new connector model for tidss

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Date:   Fri, 12 May 2023 12:20:12 +0300
From:   Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To:     Aradhya Bhatia <a-bhatia1@...com>, Jyri Sarha <jyri.sarha@....fi>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Rahul T R <r-ravikumar@...com>,
        Swapnil Jakhade <sjakhade@...ence.com>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        Francesco Dolcini <francesco@...cini.it>
Cc:     DRI Development List <dri-devel@...ts.freedesktop.org>,
        Linux Kernel List <linux-kernel@...r.kernel.org>,
        Nishanth Menon <nm@...com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Devarsh Thakkar <devarsht@...com>,
        Jayesh Choudhary <j-choudhary@...com>
Subject: Re: [PATCH v6 0/8] drm/tidss: Use new connector model for tidss

On 09/05/2023 12:30, Aradhya Bhatia wrote:
> Hi all,
> 
> I have picked up this long standing series from Nikhil Devshatwar[1].
> 
> This series moves the tidss to using new connectoe model, where the SoC
> driver (tidss) creates the connector and all the bridges are attached
> with the flag DRM_BRIDGE_ATTACH_NO_CONNECTOR. It also now creates bridge
> to support format negotiation and and 'simple' encoder to expose it to
> the userspace.
> 
> Since the bridges do not create the connector, the bus_format and
> bus_flag is set via atomic hooks.
> 
> Support format negotiations in the tfp410, sii902x and mhdp-8546 bridge
> drivers as a first step before moving the connector model.
> 
> These patches were tested on AM625-SK EVM, AM625 SoC based BeaglePlay,
> and J721E-SK. Display support for AM625 SoC has not been added upstream
> and is a WIP. To test this series on AM625 based platforms, basic
> display support patches, (for driver + devicetree), can be found in
> the "next_AttachNoConn" branch on my github fork[2].

Not exactly related to this series, but I was testing this with J7 EVM 
and a Dell DP monitor.

I'm seeing DPCD errors quite often, which also sometimes cause link 
training errors. E.g.:

cdns-mhdp8546 a000000.dp-bridge: Failed to read DPCD addr 0

cdns-mhdp8546 a000000.dp-bridge: Failed to adjust Link Training.

I tested retrying the read/write when it fails, and that seemed to help 
a bit, but not always. Are you using the firmware that's on the upstream 
linux-firmware repo?

  Tomi