linux-kernel - Re: [PATCH v2 3/5] media: sunxi: Add A10 CSI driver

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Date:   Wed, 6 Feb 2019 22:16:05 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     Hans Verkuil <hans.verkuil@...co.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        linux-media@...r.kernel.org, Andrzej Hajda <a.hajda@...sung.com>,
        Chen-Yu Tsai <wens@...e.org>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>
Subject: Re: [PATCH v2 3/5] media: sunxi: Add A10 CSI driver

Hi Sakari,

Thanks for your review, I have a few questions though, and the rest
will be addressed in the next version.

On Tue, Jan 29, 2019 at 02:39:49PM +0200, Sakari Ailus wrote:
> > +static int csi_notify_complete(struct v4l2_async_notifier *notifier)
> > +{
> > +	struct sun4i_csi *csi = container_of(notifier, struct sun4i_csi,
> > +					     notifier);
> > +	int ret;
> > +
> > +	ret = v4l2_device_register_subdev_nodes(&csi->v4l);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	ret = sun4i_csi_v4l2_register(csi);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	return media_create_pad_link(&csi->src_subdev->entity, csi->src_pad,
> > +				     &csi->vdev.entity, 0,
> > +				     MEDIA_LNK_FL_ENABLED |
> > +				     MEDIA_LNK_FL_IMMUTABLE);
> 
> This appears to create a link directly from the sensor entity to the video
> device entity. Is that intentional? I'd expect to see a CSI-2 receiver
> sub-device as well, which I don't see being created by the driver.
> 
> This is indeed a novel proposal. I have some concerns though.
> 
> The user doesn't have access to the configured media bus format (reflecting
> the format on the CSI-2 bus on receiver's side). It's thus difficult to
> figure out whether the V4L2 pixel format configured on the video node
> matches what the sensor outputs. Admittedly, we don't have a perfect
> solution to that whenever the DMA hardware supports multiple V4L2 pixel
> formats on a single media bus format. We might need to have a different
> solution for this one, should it be without that receiver sub-device.
> 
> Could you add the CSI-2 receiver sub-device, please?

Even though the name of the controller is *very* confusing, this isn't
a MIPI-CSI receiver, but a parallel one that supports RGB and BT656
buses.

> > +	csi->pad.flags = MEDIA_PAD_FL_SINK | MEDIA_PAD_FL_MUST_CONNECT;
> 
> Could you make it IMMUTABLE and ENABLED? If there is no need to disable it,
> that is.

The link is already created with those flags, and as far as I know it
doesn't exist for the pads

> > +static int csi_release(struct file *file)
> > +{
> > +	struct sun4i_csi *csi = video_drvdata(file);
> > +	int ret;
> > +
> > +	mutex_lock(&csi->lock);
> > +
> > +	ret = v4l2_fh_release(file);
> 
> v4l2_fh_release() always returns 0. I guess it could be changed to return
> void. The reason it has int is that it could be used as the release
> callback as such.
> 
> > +	v4l2_pipeline_pm_use(&csi->vdev.entity, 0);
> > +	pm_runtime_put(csi->dev);
> > +
> > +	mutex_unlock(&csi->lock);
> > +
> > +	return ret;
> > +}

Do you want me to change the construct then?

Thanks!
Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com