linux-kernel - Re: [PATCH 4/9] drm/panel: simple: add support for overriding the pixel clock polarity

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Message-ID: <20171017124504.GC27983@ulmo>
Date:   Tue, 17 Oct 2017 14:45:04 +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 4/9] drm/panel: simple: add support for overriding the
 pixel clock polarity

On Tue, Oct 17, 2017 at 02:25:07PM +0200, Lothar Waßmann wrote:
> Hi,
> 
> On Tue, 17 Oct 2017 14:14:22 +0200 Thierry Reding wrote:
> > On Wed, Oct 11, 2017 at 01:23:36PM +0200, Lothar Waßmann wrote:
> > > The Ka-Ro electronics MB7 baseboard has an on-board LCD->LVDS
> > > converter that requires a fixed pixelclk polarity, no matter what the
> > > panel's display_mode specifies. Add an option to override the pixelclk
> > > polarity defined in the panel's display_mode via DTB.
> > 
> > I'd argue that the LCD->LVDS converter should be modelled specifically
> > in DT to handle this case. It could be a implemented as a DRM bridge
> > driver, for example.
> > 
> IMO that's just overkill for a simple chip that is in no way
> configurable nor detectable by software.

I suspect that you're not the only one who runs a board that has this
kind of quirk. If we solve this in a generic way we can point people in
that direction when they come asking for such a quirk.

So this could be something very simple that's instantiated using maybe a
couple of lines of code.

Thierry

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