linux-kernel - Re: [PATCH v2] media: i2c: ov5640: Implement get_mbus

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Message-ID: <ZBBvmjUZIn/g0/Nv@francesco-nb.int.toradex.com>
Date:   Tue, 14 Mar 2023 13:59:06 +0100
From:   Francesco Dolcini <francesco@...cini.it>
To:     Sakari Ailus <sakari.ailus@....fi>
Cc:     Francesco Dolcini <francesco@...cini.it>,
        Marcel Ziswiler <marcel@...wiler.com>,
        linux-media@...r.kernel.org,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Philipp Zabel <p.zabel@...gutronix.de>, kernel@...gutronix.de,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Francesco Dolcini <francesco.dolcini@...adex.com>,
        Jacopo Mondi <jacopo.mondi@...asonboard.com>,
        Aishwarya Kothari <aishwarya.kothari@...adex.com>,
        Marcel Ziswiler <marcel.ziswiler@...adex.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Steve Longerbeam <slongerbeam@...il.com>,
        linux-kernel@...r.kernel.org,
        Marco Felsch <m.felsch@...gutronix.de>
Subject: Re: [PATCH v2] media: i2c: ov5640: Implement get_mbus_config

+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@...adex.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@...adex.com>
> > > > Signed-off-by: Marcel Ziswiler <marcel.ziswiler@...adex.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?

> I don't object having a helper in the framework to do this though. There
> are many receiver drivers that need this to work with those devices that
> have variable number of lanes.

Thanks in advance,
Francesco