linux-kernel - Re: [PATCH 3/9] drm/panel: simple: make it possible to override LCD bus format

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Message-ID: <20171017121240.GD684@ulmo>
Date:   Tue, 17 Oct 2017 14:12:40 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Lothar Waßmann <LW@...O-electronics.de>
Cc:     David Airlie <airlied@...ux.ie>,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/9] drm/panel: simple: make it possible to override LCD
 bus format

On Wed, Oct 11, 2017 at 01:23:35PM +0200, Lothar Waßmann wrote:
> The baseboards for the Ka-Ro electronics series of i.MX modules
> use a 24bit LCD interface, no matter what LCD bus width the SoC on the
> module provides and what the LCD panel expects. LCDs with 6bit per color
> will ignore the 2 LSBs of each color lane, and modules using a SoC
> that provides only 6bit per color, drive the display information on the
> 6 MSBs of each color lane and tie the 2 LSBs of each color lane to GND.
> 
> Thus, no matter what combination of LCD and SoC is used, the LCD port
> can be used without shuffling bit lanes by always configuring the LCD
> output to 24bit mode.
> 
> Add a function to handle certain quirks of the LCD interface to the
> panel driver to be able to override the bus format specified in a
> panel's display_mode.

I think the above paragraph clearly indicates that this is the wrong
place to workaround this. You say yourself that the LCD interface has
quirks that need to be handled, so why do you want to force this
handling into the panel driver?

The panel remains the same, no matter what interface you connect it to.

Thierry

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