Re: [RFCv1 11/42] ARM: dts: omap: add channel to DSI panels

From: Tony Lindgren <tony@atomide.com>
To: Sebastian Reichel <sebastian.reichel@collabora.com>
Cc: kernel@collabora.com, "H. Nikolaus Schaller" <hns@goldelico.com>,
	Merlijn Wajer <merlijn@wizzup.org>,
	dri-devel@lists.freedesktop.org,
	Tomi Valkeinen <tomi.valkeinen@ti.com>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	linux-omap@vger.kernel.org
Subject: Re: [RFCv1 11/42] ARM: dts: omap: add channel to DSI panels
Date: Mon, 18 Nov 2019 14:52:09 -0800	[thread overview]
Message-ID: <20191118225209.GF35479@atomide.com> (raw)
In-Reply-To: <20191118150301.vvnsmztfxo76ghwe@earth.universe>

* Sebastian Reichel <sebastian.reichel@collabora.com> [191118 15:03]:
> On Mon, Nov 18, 2019 at 03:37:12PM +0100, H. Nikolaus Schaller wrote:
> > > Am 18.11.2019 um 15:33 schrieb Sebastian Reichel <sebastian.reichel@collabora.com>:
> > > On Mon, Nov 18, 2019 at 03:05:07PM +0200, Tomi Valkeinen wrote:
> > >> On 17/11/2019 04:39, Sebastian Reichel wrote:
> > >>> The standard binding for DSI requires, that the channel number
> > >>> of the panel is encoded in DT. This adds the channel number in
> > >>> all OMAP3-5 boards, in preparation for using common infrastructure.
> > >>> 
> > >>> Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
> > >>> ---
> > >>>  .../devicetree/bindings/display/panel/panel-dsi-cm.txt      | 4 +++-
> > >>>  arch/arm/boot/dts/omap3-n950.dts                            | 3 ++-
> > >>>  arch/arm/boot/dts/omap3.dtsi                                | 3 +++
> > >>>  arch/arm/boot/dts/omap4-droid4-xt894.dts                    | 3 ++-
> > >>>  arch/arm/boot/dts/omap4-sdp.dts                             | 6 ++++--
> > >>>  arch/arm/boot/dts/omap4.dtsi                                | 6 ++++++
> > >>>  arch/arm/boot/dts/omap5.dtsi                                | 6 ++++++
> > >>>  7 files changed, 26 insertions(+), 5 deletions(-)
> > >> 
> > >> Is this required only in the .txt, or also by the driver? This does break
> > >> backward compatibility with the dtbs, and there's always someone who won't
> > >> like it.
> > > 
> > > I add a compatible string for the Droid 4 panel in addition to the
> > > generic one, which is not really required and just a precaution in
> > > case we need some quirks in the future.
> > > 
> > > But I had to add the DSI channel to DT, which is required to follow
> > > the standard DSI bindings. We cannot use the generic infrastructure
> > > without this change. Technically it should have been there all the
> > > time, it is only working because it is currently hardcoded to 0 in
> > > the panel driver.
> > 
> > Is it possible to change it to default to channel <0> if reg is not
> > specified?
> 
> Currently nodes without reg property are skipped by of_mipi_dsi_device_add()
> and of_mipi_dsi_device_add() fails if reg node is missing. Technically
> it should be possible to default to channel 0 there. That affects all
> platforms, though. Considering the small amount of boards affected, I think
> its better to just fix the DT. Also the fixed DT does not make problems
> with older kernels and can be backported.

You might be able to do a local fixup at driver probe time using
of_add_property(). See for example pcs_quirk_missing_pinctrl_cells()
I added earlier because of similar issues.

Regards,

Tony
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