linux-kernel - Re: [PATCH 04/21] drm/tilcdc: Add support for DRM bus flags and simplify panel config

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Message-Id: <DEUQOGYVBYFL.39NLEZ2GBI2WT@bootlin.com>
Date: Wed, 10 Dec 2025 19:13:53 +0100
From: "Luca Ceresoli" <luca.ceresoli@...tlin.com>
To: "Kory Maincent (TI.com)" <kory.maincent@...tlin.com>, "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>
Cc: "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 04/21] drm/tilcdc: Add support for DRM bus flags and
 simplify panel config

On Wed Nov 26, 2025 at 6:35 PM CET, Kory Maincent (TI.com) wrote:
> Migrate CRTC mode configuration to use standard DRM bus flags in
> preparation for removing the tilcdc_panel driver and its custom
> tilcdc_panel_info structure.
>
> Add support for DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE and
> DRM_BUS_FLAG_SYNC_DRIVE_NEGEDGE flags to control pixel clock and sync
> signal edge polarity, while maintaining backward compatibility with the
> existing tilcdc panel info structure.
>
> Simplify several hardware parameters by setting them to fixed defaults
> based on common usage across existing device trees:
> - DMA burst size: 16 (previously configurable via switch statement)
> - AC bias frequency: 255 (previously panel-specific)
> - FIFO DMA request delay: 128 (previously panel-specific)
>
> These parameters show no variation in real-world usage, so hardcoding
> them simplifies the driver without losing functionality.
>
> Preserve FIFO threshold configurability by adding a new "fifo-threshold"
> device tree property at the display controller level, as this parameter
> varies across different display configurations in existing device trees.
>
> Signed-off-by: Kory Maincent (TI.com) <kory.maincent@...tlin.com>

Apart from the "fifo-threshold" property, which as discussed should instead
be inferred from the compatible, the patch looks good. I checked the values
which are being removed and they have all the same value in the code
defaults and all in-tree dts files.

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com