Date:   Wed, 2 Dec 2020 15:19:11 +0100
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-sunxi@...glegroups.com, Yong Deng <yong.deng@...ewell.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Jonathan Corbet <corbet@....net>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>,
        Helen Koike <helen.koike@...labora.com>,
        Dafna Hirschfeld <dafna.hirschfeld@...labora.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        kevin.lhopital@...mail.com
Subject: Re: [PATCH v2 07/19] media: sun6i-csi: Add support for MIPI CSI-2
 bridge input

Hi,

On Tue 01 Dec 20, 13:12, Maxime Ripard wrote:
> Hi,
> 
> On Sat, Nov 28, 2020 at 03:28:27PM +0100, Paul Kocialkowski wrote:
> > The A31 CSI controller supports a MIPI CSI-2 bridge input, which has
> > its own dedicated port in the fwnode graph.
> > 
> > Support for this input is added with this change:
> > - two pads are defined for the media entity instead of one
> >   and only one needs to be connected at a time;
> > - the pads currently match the fwnode graph representation;
> > - links are created between our pads and the subdevs for each
> >   interface and are no longer immutable so that userspace can select
> >   which interface to use in case both are bound to a subdev;
> > - fwnode endpoints are parsed and stored for each interface;
> > - the active subdev (and fwnode endpoint) is retrieved when validating
> >   the media link at stream on time and cleared at stream off;
> > - an error is raised if both links are active at the same time;
> > - the MIPI interface bit is set if the MIPI CSI-2 bridge endpoint is
> >   active.
> > 
> > In the future, the media entity representation might evolve to:
> > - distinguish the internal parallel bridge and data formatter;
> > - represent each of the 4 internal channels that can exist between
> >   the parallel bridge (for BT656 time-multiplex) and MIPI CSI-2
> >   (internal channels can be mapped to virtual channels);
> > - connect the controller's output to the ISP instead of its
> >   DMA engine.
> > 
> > Finally note that the MIPI CSI-2 bridges should not be linked in
> > the fwnode graph unless they have a sensor subdev attached.
> 
> I'll leave most of the review to Laurent and Sakari, but I'm not quite
> sure what you meant in the last paragraph. Did you mean that the
> MIPI-CSI controller in the Allwinner SoC should only be linked if it has
> a sensor attached, or did you mean that any MIPI-CSI2 bridge cannot be
> attached to the controller?

So the use of plural was a mistake and your first understanding is the correct
one: if the bridge is linked to the CSI controller in the OF graph but the
bridge doesn't have a sensor attached, the CSI controller driver will fail
to probe, as far as I could see.

I haven't investigated much but it looks like this is expected behavior.

> Also, having somewhere (like your cover letter) the media-ctl setup you
> tested with would be great.

Understood!

Cheers,

Paul

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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