Re: [RESEND PATCH v3 06/11] drm: add DT bindings documentation for atmel-hlcdc-dc driver

From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Thierry Reding <thierry.reding@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	devicetree@vger.kernel.org,
	Nicolas Ferre <nicolas.ferre@atmel.com>,
	dri-devel@lists.freedesktop.org,
	Alexandre Belloni <alexandre.belloni@free-electrons.com>,
	Bo Shen <voice.shen@atmel.com>, Lee Jones <lee.jones@linaro.org>,
	Jean-Jacques Hiblot <jjhiblot@traphandler.com>,
	Samuel Ortiz <sameo@linux.intel.com>,
	Tim Niemeyer <tim.niemeyer@corscience.de>,
	Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>,
	linux-pwm@vger.kernel.org, Pawel Moll <pawel.moll@arm.com>,
	Ian Campbell <ijc+devicetree@hellion.org.uk>,
	Rob Herring <robh+dt@kernel.org>,
	Andrew Victor <linux@maxim.org.za>,
	linux-arm-kernel@lists.infradead.org,
	Thomas Petazzoni <thomas.petazzoni@free-electrons.com>,
	Kumar Gala <galak@codeaurora.org>
Subject: Re: [RESEND PATCH v3 06/11] drm: add DT bindings documentation for atmel-hlcdc-dc driver
Date: Mon, 21 Jul 2014 15:26:12 +0200	[thread overview]
Message-ID: <2273675.A51UonkrgF@avalon> (raw)
In-Reply-To: <20140721125624.GF15238@ulmo>

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Hi Thierry,

On Monday 21 July 2014 14:56:26 Thierry Reding wrote:
> On Mon, Jul 21, 2014 at 02:33:21PM +0200, Boris BREZILLON wrote:
> > On Mon, 21 Jul 2014 14:15:16 +0200 Thierry Reding wrote:
> >> On Fri, Jul 18, 2014 at 04:51:52PM +0200, Boris BREZILLON wrote:
> >>> On Tue, 15 Jul 2014 12:31:37 +0200 Thierry Reding wrote:
> >>>> On Tue, Jul 15, 2014 at 12:06:19PM +0200, Boris BREZILLON wrote:
> >>>>> On Mon, 14 Jul 2014 12:05:43 +0200 Thierry Reding wrote:
> >>>>>> On Mon, Jul 07, 2014 at 06:42:59PM +0200, Boris BREZILLON wrote:

[snip]

> >>>>>>> + - atmel,panel: Should contain a phandle with 2 parameters.
> >>>>>>> +   The first cell is a phandle to a DRM panel device
> >>>>>>> +   The second cell encodes the RGB mode, which can take the
> >>>>>>> following values: +   * 0: RGB444
> >>>>>>> +   * 1: RGB565
> >>>>>>> +   * 2: RGB666
> >>>>>>> +   * 3: RGB888
> >>>>>> 
> >>>>>> These are properties of the panel and should be obtained from
> >>>>>> the panel directly rather than an additional cell in this
> >>>>>> specifier.
> >>>>> 
> >>>>> Okay.
> >>>>> What's the preferred way of doing this ?
> >>>>> What about defining an rgb-mode property in the panel node.

[snip]

> >>>> Also, like Laurent said, this shouldn't go into the device tree,
> >>>> since it's already implied by the panel's compatible value, so we'd
> >>>> be duplicating information.
> >>> 
> >>> Again, this is not necessarily true (depending on your board design).
> >>> One can decide to connect an RGB888 panel on an RGB666 bus and connect
> >>> the missing pins to ground.
> >> 
> >> I think in that case the board design itself could be considered as an
> >> RGB888 to RGB666 bridge, and I think that's what the device tree should
> >> be describing rather than a panel with a variable number of input
> >> formats.
> > 
> > So, you're suggesting to add an RGB to RGB drm_bridge driver (and
> > the appropriate DT bindings) to handle this case, right ?
> 
> Yes, exactly.

Wouldn't it be possible to implement RGB666 -> RGB888 support in a less 
complex way ? A standalone driver to describe signal routing seems like an 
overly complex solution to me. I would prefer making the routing a properly of 
the link instead of a separate device.

-- 
Regards,

Laurent Pinchart

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