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

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Date:   Tue, 23 Nov 2021 08:38:47 +0100
From:   Alexander Stein <alexander.stein@...tq-group.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Adam Ford <aford173@...il.com>
Cc:     arm-soc <linux-arm-kernel@...ts.infradead.org>,
        Tim Harvey <tharvey@...eworks.com>,
        Schrempf Frieder <frieder.schrempf@...tron.de>,
        linux-media <linux-media@...r.kernel.org>,
        Adam Ford-BE <aford@...conembedded.com>,
        cstevens@...conembedded.com,
        Jagan Teki <jagan@...rulasolutions.com>,
        Rob Herring <robh+dt@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Lucas Stach <l.stach@...gutronix.de>,
        Peng Fan <peng.fan@....com>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: (EXT) Re: [PATCH V2 4/5] arm64: dts: imx8mm-beacon: Enable
 OV5640 Camera

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@...il.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