linux-kernel - Re: [PATCH] drm/panel: simple: Support reset GPIOs

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Message-ID: <20191216115331.5c6047f7@xps13>
Date:   Mon, 16 Dec 2019 11:53:31 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH] drm/panel: simple: Support reset GPIOs

Hi Sam,

Sam Ravnborg <sam@...nborg.org> wrote on Sat, 14 Dec 2019 11:23:54
+0100:

> Hi Miquel.
> 
> On Fri, Dec 13, 2019 at 07:13:25PM +0100, Miquel Raynal wrote:
> > The panel common bindings provide a gpios-reset property which is
> > active low by default. Let's support it in the simple driver.
> > 
> > De-asserting the reset pin implies a physical high, which in turns is
> > a logic low.
> > 
> > Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>  
> 
> Code looks fine - but I fail to see why simple panels would require a
> reset pin.
> 
> Do you have any simple panels that requires this, or did you add it
> because you saw it in the panel-common.yaml file?

My hardware is:

LVDS IP <----------> LVDS to RGB bridge <------------> Panel

While there is a simple "RGB to LVDS" bridge driver, there is none
doing the work the other way around. In my case, the bridge has a reset
pin.

As until now there is no way to represent the "LVDS to RGB" bridge and
because the bindings already document such reset pin, I decided to add
support for it in the simple panel driver.

Thanks,
Miquèl