Re: (EXT) Re: [PATCH V2 4/5] arm64: dts: imx8mm-beacon: Enable OV5640 Camera

From: Alexander Stein <alexander.stein@ew.tq-group.com>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Adam Ford <aford173@gmail.com>
Cc: arm-soc <linux-arm-kernel@lists.infradead.org>,
	Tim Harvey <tharvey@gateworks.com>,
	Schrempf Frieder <frieder.schrempf@kontron.de>,
	linux-media <linux-media@vger.kernel.org>,
	Adam Ford-BE <aford@beaconembedded.com>,
	cstevens@beaconembedded.com,
	Jagan Teki <jagan@amarulasolutions.com>,
	Rob Herring <robh+dt@kernel.org>, Shawn Guo <shawnguo@kernel.org>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	Pengutronix Kernel Team <kernel@pengutronix.de>,
	Fabio Estevam <festevam@gmail.com>,
	NXP Linux Team <linux-imx@nxp.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Lucas Stach <l.stach@pengutronix.de>, Peng Fan <peng.fan@nxp.com>,
	devicetree <devicetree@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: (EXT) Re: [PATCH V2 4/5] arm64: dts: imx8mm-beacon: Enable OV5640 Camera
Date: Tue, 23 Nov 2021 08:38:47 +0100	[thread overview]
Message-ID: <0c3b4cdd075919ca5cc27c56e792f510e3b76cd7.camel@ew.tq-group.com> (raw)
In-Reply-To: <YZwyhWPJVlC0JmpK@pendragon.ideasonboard.com>

Am Dienstag, dem 23.11.2021 um 02:15 +0200 schrieb Laurent Pinchart:
> Hi Adam,
> 
> On Sun, Nov 21, 2021 at 09:07:26PM -0600, Adam Ford wrote:
> > On Sun, Nov 21, 2021 at 5:18 PM Laurent Pinchart wrote:
> > > On Sat, Nov 06, 2021 at 10:54:26AM -0500, Adam Ford wrote:
> > > > The baseboard has support for a TDNext 5640 Camera which
> > > > uses an OV5640 connected to a 2-lane CSI2 interface.
> > > > 
> > > > With the CSI and mipi_csi2 drivers pointing to an OV5640
> > > > camera, the media
> > > > pipeline can be configured with the following:
> > > > 
> > > >     media-ctl --links "'ov5640 1-003c':0->'imx7-mipi-
> > > > csis.0':0[1]"
> > > > 
> > > > The camera and various nodes in the pipeline can be configured
> > > > for UYVY:
> > > >     media-ctl -v -V "'ov5640 1-003c':0 [fmt:UYVY8_1X16/640x480
> > > > field:none]"
> > > >     media-ctl -v -V "'csi':0 [fmt:UYVY8_1X16/640x480
> > > > field:none]"
> > > > 
> > > > Signed-off-by: Adam Ford <
> > > > aford173@gmail.com
> > > > >
> > > 
> > > As the ov5640 is on an add-on module, would a DT overlay be
> > > better ?
> > 
> > At least for the Beacon / LogicPD boards, I would prefer to avoid
> > the
> > overlays.  We have an i.M6Q and an OMAP3 board with cameras enabled
> > in
> > our development kit device trees.  If the cameras are not
> > connected,
> > they just display a message that the cameras are not communicating
> > and
> > move on.  I'm OK with that.
> 
> You know the board better than I do, so I won't push against this,
> but I
> still think it may not lead to the best user experience, especially
> if a
> user wanted to connect a different sensor to the development board.

I see the advantages of overlays compared to "stacked" .dts files. But
is there any general supported interface how to actually apply an
overlay?
Documentation/devicetree/overlay-notes.rst
states of_overlay_fdt_apply() but there is only exactly one user in-
kernel (rcar-du). Is it expected that the bootloader like u-boot shall
apply the .dtbo files?

Best regards,
Alexander