Re: [RFC PATCH 0/3] drm/panel: Support panel detection

From: Boris Brezillon <boris.brezillon@bootlin.com>
To: Eric Anholt <eric@anholt.net>
Cc: David Airlie <airlied@linux.ie>,
	Thierry Reding <thierry.reding@gmail.com>,
	dri-devel@lists.freedesktop.org
Subject: Re: [RFC PATCH 0/3] drm/panel: Support panel detection
Date: Mon, 30 Apr 2018 19:43:26 +0200	[thread overview]
Message-ID: <20180430194326.2fd3e6d2@bbrezillon> (raw)
In-Reply-To: <87d0ygzk1g.fsf@anholt.net>

On Mon, 30 Apr 2018 10:22:19 -0700
Eric Anholt <eric@anholt.net> wrote:

> Boris Brezillon <boris.brezillon@bootlin.com> writes:
> 
> > Some panels are connected through extension boards an provide an easy
> > way for the main board to detect when they are present (like checking
> > for a working I2C communication with a device and making sure a
> > specific reg in this device has a consistent value).
> >
> > When this is the case, we might want to support dynamic panel detection
> > and only expose the display (and its display modes) when the panel is
> > detected, similar to the monitor detection we use for regular
> > connectors (HDMI, DVI, ...).
> >
> > This solves a problem we have on the Rpi when the panel is not
> > connected to the board but described in the DT. This prevents the whole
> > display pipeline from being exposed because one of the element (the
> > panel) is missing.
> >
> > This was posted as an RFC because I'm not sure dynamically detecting
> > panels or supporting panel hotplug is actually something we want to do.  
> 
> I want to clarify here: we're not trying to do panel hotplug.  We're
> trying to boot-time-only detection of whether or not the standard panel
> is plugged in.
> 
> Since this is something like the 6th variation of trying to get this
> driver to work whether or not the panel is plugged in at boot, I'm
> leaning toward just asking the closed source firmware to hack the DT to
> add/remove the panel's node depending on whether it can probe it on I2C.
> Relying on more closed source software in order to work around something
> so trivial is really frustrating, though.

Well, we could still have this hack in the rpi-touchscreen-panel driver
and expose the panel without any display modes when the device is
actually not responding on the I2C bus. This way we could have the DRM
device registered and the panel display would just be unusable.
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