Message-ID: <20171219132854.rw5mgjylz2uxoewz@valkosipuli.retiisi.org.uk>
Date:   Tue, 19 Dec 2017 15:28:55 +0200
From:   Sakari Ailus <sakari.ailus@....fi>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     jacopo mondi <jacopo@...ndi.org>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        magnus.damm@...il.com, geert@...der.be, mchehab@...nel.org,
        hverkuil@...all.nl, linux-renesas-soc@...r.kernel.org,
        linux-media@...r.kernel.org, linux-sh@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 03/10] v4l: platform: Add Renesas CEU driver

Heippa!

On Tue, Dec 19, 2017 at 03:07:41PM +0200, Laurent Pinchart wrote:
> Hi Jacopo,
> 
> (CC'ing Sakari)
> 
> On Tuesday, 19 December 2017 13:57:42 EET jacopo mondi wrote:
> > On Mon, Dec 11, 2017 at 06:15:23PM +0200, Laurent Pinchart wrote:
> > > Hi Jacopo,
> > > 
> > > Thank you for the patch.
> > > 
> > > [snip]
> > > 
> > >> +static int ceu_sensor_bound(struct v4l2_async_notifier *notifier,
> > >> +			    struct v4l2_subdev *v4l2_sd,
> > >> +			    struct v4l2_async_subdev *asd)
> > >> +{
> > >> +	struct v4l2_device *v4l2_dev = notifier->v4l2_dev;
> > >> +	struct ceu_device *ceudev = v4l2_to_ceu(v4l2_dev);
> > >> +	struct ceu_subdev *ceu_sd = to_ceu_subdev(asd);
> > >> +
> > >> +	if (video_is_registered(&ceudev->vdev)) {
> > >> +		v4l2_err(&ceudev->v4l2_dev,
> > >> +			 "Video device registered before this sub-device.\n");
> > >> +		return -EBUSY;
> > > 
> > > Can this happen ?
> > > 
> > >> +	}
> > >> +
> > >> +	/* Assign subdevices in the order they appear */
> > >> +	ceu_sd->v4l2_sd = v4l2_sd;
> > >> +	ceudev->num_sd++;
> > >> +
> > >> +	return 0;
> > >> +}
> > >> +
> > > > +static int ceu_sensor_complete(struct v4l2_async_notifier *notifier)
> > > > +{
> > > > +	struct v4l2_device *v4l2_dev = notifier->v4l2_dev;
> > > > +	struct ceu_device *ceudev = v4l2_to_ceu(v4l2_dev);
> > > > +	struct video_device *vdev = &ceudev->vdev;
> > > > +	struct vb2_queue *q = &ceudev->vb2_vq;
> > > > +	struct v4l2_subdev *v4l2_sd;
> > > > +	int ret;
> > > > +
> > > > +	/* Initialize vb2 queue */
> > > > +	q->type			= V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
> > > > +	q->io_modes		= VB2_MMAP | VB2_USERPTR;
> > > 
> > > No dmabuf ?
> > > 
> > > > +	q->drv_priv		= ceudev;
> > > > +	q->ops			= &ceu_videobuf_ops;
> > > > +	q->mem_ops		= &vb2_dma_contig_memops;
> > > > +	q->buf_struct_size	= sizeof(struct ceu_buffer);
> > > > +	q->timestamp_flags	= V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
> > > > +	q->lock			= &ceudev->mlock;
> > > > +	q->dev			= ceudev->v4l2_dev.dev;
> > > 
> > > [snip]
> > > 
> > > > +static int ceu_probe(struct platform_device *pdev)
> > > > +{
> > > > +	struct device *dev = &pdev->dev;
> > > > +	struct ceu_device *ceudev;
> > > > +	struct resource *res;
> > > > +	void __iomem *base;
> > > > +	unsigned int irq;
> > > > +	int num_sd;
> > > > +	int ret;
> > > > +
> > > > +	ceudev = kzalloc(sizeof(*ceudev), GFP_KERNEL);
> > > 
> > > The memory is freed in ceu_vdev_release() as expected, but that will only
> > > work if the video device is registered. If the subdevs are never bound,
> > > the ceudev memory will be leaked if you unbind the CEU device from its
> > > driver. In my opinion this calls for registering the video device at
> > > probe time (although Hans disagrees).
> > > 
> > > > +	if (!ceudev)
> > > > +		return -ENOMEM;
> > > > +
> > > > +	platform_set_drvdata(pdev, ceudev);
> > > > +	dev_set_drvdata(dev, ceudev);
> > > 
> > > You don't need the second line, platform_set_drvdata() is a wrapper around
> > > dev_set_drvdata().
> > > 
> > > > +	ceudev->dev = dev;
> > > > +
> > > > +	INIT_LIST_HEAD(&ceudev->capture);
> > > > +	spin_lock_init(&ceudev->lock);
> > > > +	mutex_init(&ceudev->mlock);
> > > > +
> > > > +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > > > +	if (IS_ERR(res))
> > > > +		return PTR_ERR(res);
> > > 
> > > No need for error handling here, devm_ioremap_resource() will check the
> > > res
> > > pointer.
> > > 
> > > > +	base = devm_ioremap_resource(dev, res);
> > > 
> > > You can assign ceudev->base directly and remove the base local variable.
> > > 
> > > > +	if (IS_ERR(base))
> > > > +		return PTR_ERR(base);
> > > > +	ceudev->base = base;
> > > > +
> > > > +	ret = platform_get_irq(pdev, 0);
> > > > +	if (ret < 0) {
> > > > +		dev_err(dev, "failed to get irq: %d\n", ret);
> > > > +		return ret;
> > > > +	}
> > > > +	irq = ret;
> > > > +
> > > > +	ret = devm_request_irq(dev, irq, ceu_irq,
> > > > +			       0, dev_name(dev), ceudev);
> > > > +	if (ret) {
> > > > +		dev_err(&pdev->dev, "Unable to register CEU interrupt.\n");
> > > > +		return ret;
> > > > +	}
> > > > +
> > > > +	pm_suspend_ignore_children(dev, true);
> > > > +	pm_runtime_enable(dev);
> > > > +
> > > > +	ret = v4l2_device_register(dev, &ceudev->v4l2_dev);
> > > > +	if (ret)
> > > > +		goto error_pm_disable;
> > > > +
> > > > +	if (IS_ENABLED(CONFIG_OF) && dev->of_node) {
> > > > +		num_sd = ceu_parse_dt(ceudev);
> > > > +	} else if (dev->platform_data) {
> > > > +		num_sd = ceu_parse_platform_data(ceudev, dev->platform_data);
> > > > +	} else {
> > > > +		dev_err(dev, "CEU platform data not set and no OF support\n");
> > > > +		ret = -EINVAL;
> > > > +		goto error_v4l2_unregister;
> > > > +	}
> > > > +
> > > > +	if (num_sd < 0) {
> > > > +		ret = num_sd;
> > > > +		goto error_v4l2_unregister;
> > > > +	} else if (num_sd == 0)
> > > > +		return 0;
> > > 
> > > You need braces around the second statement too.
> > 
> > Ok, actually parse_dt() and parse_platform_data() behaves differently.
> > The former returns error if no subdevices are connected to CEU, the
> > latter returns 0. That's wrong.
> > 
> > I wonder what's the correct behavior here. Other mainline drivers I
> > looked into (pxa_camera and atmel-isc) behaves differently from each
> > other, so I guess this is up to each platform to decide.
> 
> No, what it means is that we've failed to standardize it, not that it 
> shouldn't be standardized :-)
> 
> > Also, the CEU can accept one single input (and I made it clear
> > in DT bindings documentation saying it accepts a single endpoint,
> > while I'm parsing all the available ones in driver, I will fix this)
> > but as it happens on Migo-R, there could be HW hacks to share the input
> > lines between multiple subdevices. Should I accept it from dts as well?
> > 
> > So:
> > 1) Should we fail to probe if no subdevices are connected?
> 
> While the CEU itself would be fully functional without a subdev, in practice 
> it would be of no use. I would thus fail probing.
> 
> > 2) Should we accept more than 1 subdevice from dts as it happens right
> > now for platform data?
> 
> We need to support multiple connected devices, as some of the boards require 
> that. What I'm not sure about is whether the multiplexer on the Migo-R board 
> should be modeled as a subdevice. We could in theory connect multiple sensors 
> to the CEU input signals without any multiplexer as long as all but one are in 
> reset with their outputs in a high impedance state. As that wouldn' require a 
> multiplexer we would need to support multiple endpoints in the CEU port. We 
> could then support Migo-R the same way, making the multiplexer transparent.
> 
> Sakari, what would you do here ?

We do have:

drivers/media/platform/video-mux.c

What is not addressed right now are the CSI-2 bus parameters, if the mux is
just a passive switch. This could be done using the frame descriptors.

-- 
Sakari Ailus
e-mail: sakari.ailus@....fi

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