Custom device names for v4l2 devices
Hi
Names of V4L2 device nodes keep on varying depending on target, on some targets, the device node assigned to my device is /dev/video21 and on some it is /dev/video15. In order to determine my device, i am opening it, reading the capabilities, enumerating its formats and then chose the one matching my requirements. This is impacting start-up latency. One way to resolve this without impacting start-up latency is to give custom name to my V4L2 device node (/dev/custom_name instead of /dev/video21). This needs following change in V4L2 framework. Please review this patch. If you have faced similar problem please let me know.
drivers/media/video/v4l2-dev.c +0 -0
@@ -676,7 +676,8 @@ int __video_register_device(struct video_device *vdev,
int type, int nr,
vdev->dev.devt = MKDEV(VIDEO_MAJOR, vdev->minor);
if (vdev->parent)
vdev->dev.parent = vdev->parent;
- dev_set_name(&vdev->dev, "%s%d", name_base, vdev->num);
+ if (!dev_name(&vdev->dev))
+ dev_set_name(&vdev->dev, "%s%d", name_base, vdev->num);
ret = device_register(&vdev->dev);
if (ret < 0) {
printk(KERN_ERR "%s: device_register failed\n", __func__);
Thanks
Vinay
Please suggest.
Thanks
Vinay
Quoted 30 lines
Hi
Names of V4L2 device nodes keep on varying depending on target, on some targets, the device node assigned to my device is
/dev/video21and on some it is/dev/video15. In order to determine my device, i am opening it, reading the capabilities, enumerating its formats and then chose the one matching my requirements. This is impacting start-up latency. One way to resolve this without impacting start-up latency is to give custom name to my V4L2 device node (/dev/custom_nameinstead of/dev/video21). This needs following change in V4L2 framework. Please review this patch. If you have faced similar problem please let me know.drivers/media/video/v4l2-dev.c +2
-1@@ -676,7 +676,8 @@ int __video_register_device(struct video_device *vdev, int type, int nr, vdev->dev.devt = MKDEV(VIDEO_MAJOR, vdev->minor);if (vdev->parent) vdev->dev.parent = vdev->parent; -dev_set_name (&vdev->dev,"%s%d" , name_base, vdev->num); +if (!dev_name (&vdev->dev)) +dev_set_name (&vdev->dev,"%s%d" , name_base, vdev->num); ret =device_register (&vdev->dev);if (ret <0 ) {
printk(KERN_ERR "%s: device_register failed\n", __func__);Thanks
Vinay
Hi Vinay,
Quoted 9 lines · On Monday 11 March 2013 10:55:37 [email protected] wrote:
Quoted 9 lines
Names of V4L2 device nodes keep on varying depending on target, on some targets, the device node assigned to my device is
/dev/video21and on some it is/dev/video15. In order to determine my device, i am opening it, reading the capabilities, enumerating its formats and then chose the one matching my requirements. This is impacting start-up latency. One way to resolve this without impacting start-up latency is to give custom name to my V4L2 device node (/dev/custom_nameinstead of/dev/video21). This needs following change in V4L2 framework. Please review this patch. If you have faced similar problem please let me know.
Shouldn't this be implemented in userspace as udev rules instead ?
Quoted 18 lines
Quoted 18 lines
drivers/media/video/v4l2-dev.c +2
-1@@ -676,7 +676,8 @@ int __video_register_device(struct video_device *vdev, int type, int nr, vdev->dev.devt = MKDEV(VIDEO_MAJOR, vdev->minor);if (vdev->parent) vdev->dev.parent = vdev->parent; -dev_set_name (&vdev->dev,"%s%d" , name_base, vdev->num); +if (!dev_name (&vdev->dev)) +dev_set_name (&vdev->dev,"%s%d" , name_base, vdev->num); ret =device_register (&vdev->dev);if (ret <0 ) {printk (KERN_ERR "%s: device_register failed\n" , __func__);
Signature · 3 lines
Regards, Laurent Pinchart
Quoted 13 lines · Laurent Pinchart
Hi Vinay,
Quoted 9 lines · On Monday 11 March 2013 10:55:37 [email protected] wrote:
Quoted 9 lines
Names of V4L2 device nodes keep on varying depending on target, on some targets, the device node assigned to my device is
/dev/video21and on some it is/dev/video15. In order to determine my device, i am opening it, reading the capabilities, enumerating its formats and then chose the one matching my requirements. This is impacting start-up latency. One way to resolve this without impacting start-up latency is to give custom name to my V4L2 device node (/dev/custom_nameinstead of/dev/video21). This needs following change in V4L2 framework. Please review this patch. If you have faced similar problem please let me know.
Quoted 1 line
Shouldn't this be implemented in userspace as udev rules instead ?
Indeed, this is possible; I use it to provide consistent names for my MythTV installation. If you have different V4L devices, you could have a utility that probes the capabilities when the device is discovered and use its output to add appropriate symlinks -- for example
IMPORT{program}="your/utility/here $tempnode" ENV{YOUR_EXPORTED_VAR_VBI_SUPPORT}=="yes", SYMLINK+="v4l/hd-capable/video"
That that would need some tweaks to handle multiple devices (ie, naming) that I didn't go look up the escapes for.
Here's my set from home to give you more grist for the mill:
$ cat /etc/udev/rules.d/60-persistent-capture.rules # Give a persistent name for MythTV to use # ACTION=="remove", GOTO="name_video_end" SUBSYSTEM!="video4linux", GOTO="name_video_end"
IMPORT{program}="v4l_id $tempnode"
#IMPORT{program}="path_id %p"
SUBSYSTEMS=="usb", IMPORT{program}="usb_id --export %p"
KERNEL=="video*", ENV{ID_SERIAL}=="Hauppauge_Hauppauge_Device_4034580546", SYMLINK+="v4l/HVR850/video" KERNEL=="vbi*", ENV{ID_SERIAL}=="Hauppauge_Hauppauge_Device_4034580546", SYMLINK+="v4l/HVR850/vbi"
# These no longer work; we stopped getting a PCI device path from the kernel it seems... #KERNEL=="video*", ENV{ID_PATH}=="pci-0000:04:00.0", SYMLINK+="v4l/WinTV/video" #KERNEL=="vbi*", ENV{ID_PATH}=="pci-0000:04:00.0", SYMLINK+="v4l/WinTV/vbi"
# Key off of the product name now that we cannot tie it to the PCI path KERNEL=="video*", ENV{ID_V4L_PRODUCT}=="Hauppauge WinTV 34xxx models", SYMLINK+="v4l/WinTV/video" KERNEL=="vbi*", ENV{ID_V4L_PRODUCT}=="Hauppauge WinTV 34xxx models", SYMLINK+="v4l/WinTV/vbi"
LABEL="name_video_end"