Date:   Mon, 20 Mar 2023 11:00:36 +0200
From:   Sakari Ailus <sakari.ailus@linux.intel.com>
To:     Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Cc:     Francesco Dolcini <francesco@dolcini.it>,
        Sakari Ailus <sakari.ailus@iki.fi>,
        Marcel Ziswiler <marcel@ziswiler.com>,
        linux-media@vger.kernel.org,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Philipp Zabel <p.zabel@pengutronix.de>, kernel@pengutronix.de,
        Francesco Dolcini <francesco.dolcini@toradex.com>,
        Aishwarya Kothari <aishwarya.kothari@toradex.com>,
        Marcel Ziswiler <marcel.ziswiler@toradex.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Steve Longerbeam <slongerbeam@gmail.com>,
        linux-kernel@vger.kernel.org,
        Marco Felsch <m.felsch@pengutronix.de>
Subject: Re: [PATCH v2] media: i2c: ov5640: Implement get_mbus_config
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Hi Jacopo,

On Mon, Mar 20, 2023 at 09:48:44AM +0100, Jacopo Mondi wrote:
> Hello
> 
> On Tue, Mar 14, 2023 at 01:59:06PM +0100, Francesco Dolcini wrote:
> > +Marco
> >
> > On Tue, Mar 14, 2023 at 02:45:53PM +0200, Sakari Ailus wrote:
> > > On Tue, Mar 14, 2023 at 01:32:16PM +0100, Francesco Dolcini wrote:
> > > > On Tue, Mar 14, 2023 at 02:13:46PM +0200, Sakari Ailus wrote:
> > > > > On Mon, Mar 06, 2023 at 07:36:49AM +0100, Marcel Ziswiler wrote:
> > > > > > From: Aishwarya Kothari <aishwarya.kothari@toradex.com>
> > > > > >
> > > > > > Implement the introduced get_mbus_config operation to report the
> > > > > > config of the MIPI CSI-2, BT.656 and Parallel interface.
> > > > > >
> > > > > > Signed-off-by: Aishwarya Kothari <aishwarya.kothari@toradex.com>
> > > > > > Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
> > > > >
> > > > > What's the reasoning for this patch?
> > > >
> > > > Without this it's not possible to use it on i.MX6,
> > > > drivers/staging/media/imx/imx6-mipi-csi2.c requires it, some more
> > > > details from Jacopo here [0].
> > > >
> > > > Everything used to work fine up to v5.18, after that kernel version
> > > > various changes broke it [1][2] (I assume you are pretty much aware of
> > > > the history here, you commented on a few emails).
> > > >
> > > > [0] https://lore.kernel.org/all/20230128100611.7ulsfqqqgscg54gy@uno.localdomain/
> > > > [1] https://lore.kernel.org/all/081cc2d3-1f3a-6c14-6dc7-53f976be7b2b@gmail.com/
> > > > [2] https://lore.kernel.org/all/cacfe146-101b-35b3-5f66-1a1cabfd342f@gmail.com/
> > > >
> > > > > Drivers that don't have e.g. dynamic lane configuration shouldn't need to
> > > > > implement get_mbus_config.
> > >
> > > Not even for staging drivers. The driver should be fixed to get that
> > > information from the endpoint instead.
> >
> > This seems exactly the opposite of what commit
> > 7318abface48 ("media: imx: Use get_mbus_config instead of parsing upstream DT endpoints")
> > did.
> >
> > Given that I am somehow confused, but I am not that familiar with this
> > subsystem, so I guess this is expected :-). Can someone provide some
> > additional hint here?
> >
> 
> As per my understanding, the i.MX6 IPU CSI driver connects to the
> CSI-2 receiver and/or two video muxes. One figure's worth a thousands
> words: "Figure 19-1. CSI2IPU gasket connectivity" of the IMX6DQRM TRM.

I don't have that document.

> 
> So the local endpoint might not provide the required information on
> the bus configuration as it connects to a video-mux.
> 
> That's why the imx_media_pipeline_subdev() helper is used in
> csi_get_upstream_mbus_config().
> 
> My gut feeling is that it would be better to always call
> get_mbus_config() on the next subdev (the mux or the CSI-2 rx) and
> there parse the local endpoint as it's the mux or the CSI-2 rx that
> connect to the actual source.

Isn't this still a different endpoint in DT? I understand you have a single
pad with two links?

-- 
Kind regards,

Sakari Ailus