On 03/12/2017 03:10 PM, Mauro Carvalho Chehab wrote:

Em Sun, 12 Mar 2017 21:13:24 +0000
Russell King - ARM Linux [off-list ref] escreveu:

quoted

On Sun, Mar 12, 2017 at 05:59:28PM -0300, Mauro Carvalho Chehab wrote:

quoted

Yet, udev/systemd has some rules that provide an unique name for V4L
devices at /lib/udev/rules.d/60-persistent-v4l.rules. Basically, it
runs a small application (v4l_id) with creates a persistent symling
using rules like this:

	KERNEL=="video*", ENV{ID_SERIAL}=="?*", SYMLINK+="v4l/by-id/$env{ID_BUS}-$env{ID_SERIAL}-video-index$attr{index}"

Those names are stored at /dev/v4l/by-path.

This doesn't help:

$ ls -Al /dev/v4l/by-id/
total 0
lrwxrwxrwx 1 root root 13 Mar 12 19:54 usb-Sonix_Technology_Co.__Ltd._USB_2.0_Camera-video-index0 -> ../../video10
$ ls -Al /dev/v4l/by-path/
total 0
lrwxrwxrwx 1 root root 12 Mar 12 19:54 platform-2040000.vpu-video-index0 -> ../../video0
lrwxrwxrwx 1 root root 12 Mar 12 19:54 platform-2040000.vpu-video-index1 -> ../../video1
lrwxrwxrwx 1 root root 12 Mar 12 20:53 platform-capture-subsystem-video-index0 -> ../../video2
lrwxrwxrwx 1 root root 12 Mar 12 20:53 platform-capture-subsystem-video-index1 -> ../../video3
lrwxrwxrwx 1 root root 12 Mar 12 20:53 platform-capture-subsystem-video-index2 -> ../../video4
lrwxrwxrwx 1 root root 12 Mar 12 20:53 platform-capture-subsystem-video-index3 -> ../../video5
lrwxrwxrwx 1 root root 12 Mar 12 20:53 platform-capture-subsystem-video-index4 -> ../../video6
lrwxrwxrwx 1 root root 12 Mar 12 20:53 platform-capture-subsystem-video-index5 -> ../../video7
lrwxrwxrwx 1 root root 12 Mar 12 20:53 platform-capture-subsystem-video-index6 -> ../../video8
lrwxrwxrwx 1 root root 12 Mar 12 20:53 platform-capture-subsystem-video-index7 -> ../../video9
lrwxrwxrwx 1 root root 13 Mar 12 19:54 platform-ci_hdrc.0-usb-0:1:1.0-video-index0 -> ../../video10

The problem is the "platform-capture-subsystem-video-index" entries.
These themselves change order.  For instance, I now have:

- entity 72: ipu1_csi0 capture (1 pad, 1 link)
              type Node subtype V4L flags 0
              device node name /dev/video6

which means it's platform-capture-subsystem-video-index4.  Before, it
was platform-capture-subsystem-video-index2.

That's a driver problem. v4l_id gets information to build the persistent
name from the result of VIDIOC_QUERYCAP.

In the case of Exynos gsc driver, for example, the information is here:

static int gsc_m2m_querycap(struct file *file, void *fh,
			   struct v4l2_capability *cap)
{
	struct gsc_ctx *ctx = fh_to_ctx(fh);
	struct gsc_dev *gsc = ctx->gsc_dev;

	strlcpy(cap->driver, GSC_MODULE_NAME, sizeof(cap->driver));
	strlcpy(cap->card, GSC_MODULE_NAME " gscaler", sizeof(cap->card));
	snprintf(cap->bus_info, sizeof(cap->bus_info), "platform:%s",
		 dev_name(&gsc->pdev->dev));
	cap->device_caps = V4L2_CAP_STREAMING | V4L2_CAP_VIDEO_M2M_MPLANE |
		V4L2_CAP_VIDEO_CAPTURE_MPLANE |	V4L2_CAP_VIDEO_OUTPUT_MPLANE;

	cap->capabilities = cap->device_caps | V4L2_CAP_DEVICE_CAPS;
	return 0;
}

See that the bus_info there is filled with:

	snprintf(cap->bus_info, sizeof(cap->bus_info), "platform:%s", dev_name(&gsc->pdev->dev));

 From the output you printed, it seems that the i.MX6 is just doing:
	snprintf(cap->bus_info, sizeof(cap->bus_info), "platform:");
for some devices.

imx6 is setting bus_info string on all capture devices as:

snprintf(cap->bus_info, sizeof(cap->bus_info),
                  "platform:%s", dev_name(priv->dev));

dev_name(priv->dev) is the device name of the attached subdev.
So the bus_info string, at least for attached CSI subdevs, should
be "platform:imx-ipuv3-csi".

Maybe there is something else missing, I haven't had a chance to
look at this yet.

Steve

If you change the i.MX6 driver to do the same, you'll likely be able to
have unique names there too.

Regards,
Mauro