linux-kernel - Re: [PATCH 03/21] drm/tilcdc: Remove simulate_vesa

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251211104024.1e7d5c42@kmaincent-XPS-13-7390>
Date: Thu, 11 Dec 2025 10:40:24 +0100
From: Kory Maincent <kory.maincent@...tlin.com>
To: "Luca Ceresoli" <luca.ceresoli@...tlin.com>
Cc: "Jyri Sarha" <jyri.sarha@....fi>, "Tomi Valkeinen"
 <tomi.valkeinen@...asonboard.com>, "Maarten Lankhorst"
 <maarten.lankhorst@...ux.intel.com>, "Maxime Ripard" <mripard@...nel.org>,
 "Thomas Zimmermann" <tzimmermann@...e.de>, "David Airlie"
 <airlied@...il.com>, "Simona Vetter" <simona@...ll.ch>, "Rob Herring"
 <robh@...nel.org>, "Krzysztof Kozlowski" <krzk+dt@...nel.org>, "Conor
 Dooley" <conor+dt@...nel.org>, "Russell King" <linux@...linux.org.uk>,
 "Bartosz Golaszewski" <brgl@...ev.pl>, "Tony Lindgren" <tony@...mide.com>,
 "Andrzej Hajda" <andrzej.hajda@...el.com>, "Neil Armstrong"
 <neil.armstrong@...aro.org>, "Robert Foss" <rfoss@...nel.org>, "Laurent
 Pinchart" <Laurent.pinchart@...asonboard.com>, "Jonas Karlman"
 <jonas@...boo.se>, "Jernej Skrabec" <jernej.skrabec@...il.com>, "Markus
 Schneider-Pargmann" <msp@...libre.com>, "Louis Chauvet"
 <louis.chauvet@...tlin.com>, "Thomas Petazzoni"
 <thomas.petazzoni@...tlin.com>, "Miguel Gazquez"
 <miguel.gazquez@...tlin.com>, <dri-devel@...ts.freedesktop.org>,
 <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <linux-arm-kernel@...ts.infradead.org>, <linux-omap@...r.kernel.org>
Subject: Re: [PATCH 03/21] drm/tilcdc: Remove simulate_vesa_sync flag

On Wed, 10 Dec 2025 19:10:45 +0100
"Luca Ceresoli" <luca.ceresoli@...tlin.com> wrote:

> Hi Köry,
> 
> On Wed Nov 26, 2025 at 6:35 PM CET, Kory Maincent (TI.com) wrote:
> > The tilcdc hardware does not generate VESA-compliant sync signals. It
> > aligns the vertical sync (VS) on the second edge of the horizontal sync
> > (HS) instead of the first edge. To compensate for this hardware
> > behavior, the driver applies a timing adjustment in mode_fixup().
> >
> > Previously, this adjustment was conditional based on the simulate_vesa_sync
> > flag, which was only set when using external encoders. This appears
> > problematic because:
> >
> > 1. The timing adjustment seems needed for the hardware behavior regardless
> >    of whether an external encoder is used
> > 2. The external encoder infrastructure is driver-specific and being
> >    removed due to design issues
> > 3. Boards using tilcdc without bridges (e.g., am335x-evm, am335x-evmsk)
> >    may not be getting the necessary timing adjustments
> >
> > Remove the simulate_vesa_sync flag and apply the VESA sync timing
> > adjustment unconditionally, ensuring consistent behavior across all
> > configurations. While it's unclear if the previous conditional behavior
> > was causing actual issues, the unconditional adjustment better reflects
> > the hardware's characteristics.
> >
> > Signed-off-by: Kory Maincent (TI.com) <kory.maincent@...tlin.com>
> > ---
> >
> > Only few board currently use tilcdc not associated to a bridge like the
> > am335x_evm or the am335x-evmsk.  
> 
> Have you tested this change on any affected board?
> 
> The change looks good to me but without some testing it would be risky.

I have tested it on few boards but not these mainline devicetree as I don't
have them.

I have tested a tilcdc with tda998x bridge (BeagleBone Black), a tilcdc with
ti,tilcdc,panel panel (BeagleBone with LCD cape), a tilcdc with it66121 bridge
(new Beagle Bone Green Eco board with HDMI cape).
That's all the boards I have.

Regards,
-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com