Message-ID: <20201105145224.GA615923@aptenodytes>
Date:   Thu, 5 Nov 2020 15:52:24 +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,
        devel@...verdev.osuosl.org, linux-sunxi@...glegroups.com,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Yong Deng <yong.deng@...ewell.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>,
        Helen Koike <helen.koike@...labora.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Hans Verkuil <hverkuil@...all.nl>, kevin.lhopital@...mail.com
Subject: Re: [PATCH 08/14] media: sunxi: Add support for the A31 MIPI CSI-2
 controller

Hi,

On Wed 04 Nov 20, 19:56, Maxime Ripard wrote:
> On Wed, Nov 04, 2020 at 12:34:58PM +0100, Paul Kocialkowski wrote:
> > > > +	regmap_write(regmap, SUN6I_MIPI_CSI2_CFG_REG,
> > > > +		     SUN6I_MIPI_CSI2_CFG_CHANNEL_MODE(1) |
> > > > +		     SUN6I_MIPI_CSI2_CFG_LANE_COUNT(lanes_count));
> > > 
> > > It's not really clear what the channel is here? The number of virtual
> > > channels? Something else?
> > 
> > That's somewhat described in the controller documentation. Channels refers to
> > physical channels of the controller, which can be used to redirect data
> > matching either a specific data type, a specific virtual channel, or both.
> > There's a somewhat similar concept of channels in the CSI controller too.
> > 
> > We're currently only using one...
> > 
> > > > +	regmap_write(regmap, SUN6I_MIPI_CSI2_VCDT_RX_REG,
> > > > +		     SUN6I_MIPI_CSI2_VCDT_RX_CH_VC(3, 3) |
> > > > +		     SUN6I_MIPI_CSI2_VCDT_RX_CH_VC(2, 2) |
> > > > +		     SUN6I_MIPI_CSI2_VCDT_RX_CH_VC(1, 1) |
> > > > +		     SUN6I_MIPI_CSI2_VCDT_RX_CH_VC(0, 0) |
> > > > +		     SUN6I_MIPI_CSI2_VCDT_RX_CH_DT(0, data_type));
> > 
> > ... but it's safer to configure them all to virtual channel numbers so we don't
> > end up with multiple channels matching virtual channel 0.
> > 
> > I'll add a comment about that.
> 
> Maybe we should have pads for all of them then, even if we don't support
> changing anything?

If that's something we can add later (I think it is), I would rather do this in
a sub-sequent series to keep the current one lightweight and merged ASAP.

It would also require some investigation to find out if the MIPI CSI-2 channel
number i goes directly to the CSI controller channel number i or if some
remapping can take place.

What do you think?

> > > > +static const struct v4l2_subdev_pad_ops sun6i_mipi_csi2_subdev_pad_ops = {
> > > > +	.enum_mbus_code		= sun6i_mipi_csi2_enum_mbus_code,
> > > > +	.get_fmt		= sun6i_mipi_csi2_get_fmt,
> > > > +	.set_fmt		= sun6i_mipi_csi2_set_fmt,
> > > > +	.enum_frame_size	= sun6i_mipi_csi2_enum_frame_size,
> > > > +	.enum_frame_interval	= sun6i_mipi_csi2_enum_frame_interval,
> > > > +};
> > > > +
> > > > +/* Subdev */
> > > > +
> > > > +static const struct v4l2_subdev_ops sun6i_mipi_csi2_subdev_ops = {
> > > > +	.core		= &sun6i_mipi_csi2_subdev_core_ops,
> > > > +	.video		= &sun6i_mipi_csi2_subdev_video_ops,
> > > > +	.pad		= &sun6i_mipi_csi2_subdev_pad_ops,
> > > > +};
> > > > +
> > > > +/* Notifier */
> > > > +
> > > > +static int sun6i_mipi_csi2_notifier_bound(struct v4l2_async_notifier *notifier,
> > > > +					  struct v4l2_subdev *remote_subdev,
> > > > +					  struct v4l2_async_subdev *remote_subdev_async)
> > > > +{
> > > > +	struct v4l2_subdev *subdev = notifier->sd;
> > > > +	struct sun6i_mipi_csi2_video *video =
> > > > +		sun6i_mipi_csi2_subdev_video(subdev);
> > > > +	struct sun6i_mipi_csi2_dev *cdev = sun6i_mipi_csi2_video_dev(video);
> > > > +	int source_pad;
> > > > +	int ret;
> > > > +
> > > > +	source_pad = media_entity_get_fwnode_pad(&remote_subdev->entity,
> > > > +						 remote_subdev->fwnode,
> > > > +						 MEDIA_PAD_FL_SOURCE);
> > > > +	if (source_pad < 0)
> > > > +		return source_pad;
> > > > +
> > > > +	ret = media_create_pad_link(&remote_subdev->entity, source_pad,
> > > > +				    &subdev->entity, 0,
> > > > +				    MEDIA_LNK_FL_ENABLED |
> > > > +				    MEDIA_LNK_FL_IMMUTABLE);
> > > > +	if (ret) {
> > > > +		dev_err(cdev->dev, "failed to create %s:%u -> %s:%u link\n",
> > > > +			remote_subdev->entity.name, source_pad,
> > > > +			subdev->entity.name, 0);
> > > > +		return ret;
> > > > +	}
> > > > +
> > > > +	video->remote_subdev = remote_subdev;
> > > > +	video->remote_pad_index = source_pad;
> > > > +
> > > > +	return 0;
> > > > +}
> > > > +
> > > > +static const struct v4l2_async_notifier_operations sun6i_mipi_csi2_notifier_ops = {
> > > > +	.bound		= sun6i_mipi_csi2_notifier_bound,
> > > > +};
> > > > +
> > > > +/* Media Entity */
> > > > +
> > > > +static int sun6i_mipi_csi2_link_validate(struct media_link *link)
> > > > +{
> > > > +	struct v4l2_subdev *subdev =
> > > > +		container_of(link->sink->entity, struct v4l2_subdev, entity);
> > > > +	struct sun6i_mipi_csi2_video *video =
> > > > +		sun6i_mipi_csi2_subdev_video(subdev);
> > > > +	struct v4l2_subdev *remote_subdev;
> > > > +	struct v4l2_subdev_format format = { 0 };
> > > > +	int ret;
> > > > +
> > > > +	if (!is_media_entity_v4l2_subdev(link->source->entity))
> > > > +		return -EINVAL;
> > > > +
> > > > +	remote_subdev = media_entity_to_v4l2_subdev(link->source->entity);
> > > > +
> > > > +	format.which = V4L2_SUBDEV_FORMAT_ACTIVE;
> > > > +	format.pad = link->source->index;
> > > > +
> > > > +	ret = v4l2_subdev_call(remote_subdev, pad, get_fmt, NULL, &format);
> > > > +	if (ret)
> > > > +		return ret;
> > > > +
> > > > +	video->mbus_code = format.format.code;
> > > > +
> > > > +	return 0;
> > > > +}
> > > 
> > > I'm not really sure what you're trying to validate here?
> > 
> > The whole purpose is to retreive video->mbus_code from the subdev, like it's
> > done in the sun6i-csi driver. Maybe there is a more appropriate op to do it?
> 
> I'm not sure why you need to do that in the link_validate though?
> 
> You just need to init the pad format, and then you'll have a
> get_fmt/set_fmt for your pads.

Okay I may have misunderstood how manual/automatic propagation is supposed to
work then. The fact that this is done this way in the CSI driver maybe gave me
a bad example to follow. I'll revisit this.

> > > > +	cdev->regmap = devm_regmap_init_mmio_clk(&pdev->dev, "bus", io_base,
> > > > +						 &sun6i_mipi_csi2_regmap_config);
> > > > +	if (IS_ERR(cdev->regmap)) {
> > > > +		dev_err(&pdev->dev, "failed to init register map\n");
> > > > +		return PTR_ERR(cdev->regmap);
> > > > +	}
> > > 
> > > Yeah, so that won't work. regmap expects to have access to those
> > > registers when you enable that clock, but that won't happen since the
> > > reset line can be disabled. You would be better off using runtime_pm
> > > here.
> > 
> > I don't understand what you mean here or what the problem could be.
> > Here we're just initializing regmap and while this is done before the
> > registers are available for I/O, I don't see why it would cause any
> > issue at this point.
> 
> The regmap here is supposed to take care of the resources, except it
> only does it for some of the resources here, which kind of breaks the
> expectations. And it doesn't allow you to have the reset / clock
> sequence properly done.

I'm not following any of this. Could you break it down some more?
In particular I don't see the relationship between initializing the regmap
API (which does take IORESOURCE_MEM in) and reset / clocks.

Just initializing the regmap API for I/O mem doesn't mean that the registers
are ready for use, does it? We're not requesting any I/O operation from it
at this point.

> > The exact same thing is done in the CSI driver.
> 
> That's not an argument though, is it? :)

That's not the point, the point is rather that if this is wrong, we should fix
it in the CSI driver as well.

Paul

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

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