v4l2-dev: use parent field if the v4l2_device has no parent set.

From: Hans Verkuil <hverkuil@xs4all.nl>

Normally the parent device of v4l2_device is used as the video device
node's parent. But if it was not set, then use the parent field in the
video_device struct.

This is needed in the cx88 driver, which has one core v4l2_device but
creates multiple pci devices (one each for raw and mpeg video).

So you cannot associate the core v4l2_device with a particular PCI device,
but you can do that for each video_device.

Priority: normal

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>

1 files changed, 11 insertions, 1 deletions

diff --git a/linux/Documentation/video4linux/v4l2-framework.txt b/linux/Documentation/video4linux/v4l2-framework.txt
index 51a7b6db1..df0247ed1 100644
--- a/linux/Documentation/video4linux/v4l2-framework.txt
+++ b/linux/Documentation/video4linux/v4l2-framework.txt
@@ -91,7 +91,8 @@ NULL, then you *must* setup v4l2_dev->name before calling v4l2_device_register.
 
 The first 'dev' argument is normally the struct device pointer of a pci_dev,
 usb_device or platform_device. It is rare for dev to be NULL, but it happens
-with ISA devices, for example.
+with ISA devices or when one device creates multiple PCI devices, thus making
+it impossible to associate v4l2_dev with a particular parent.
 
 You unregister with:
 
@@ -414,6 +415,15 @@ You should also set these fields:
 - ioctl_ops: if you use the v4l2_ioctl_ops to simplify ioctl maintenance
   (highly recommended to use this and it might become compulsory in the
   future!), then set this to your v4l2_ioctl_ops struct.
+- parent: you only set this if v4l2_device was registered with NULL as
+  the parent device struct. This only happens in cases where one hardware
+  device has multiple PCI devices that all share the same v4l2_device core.
+
+  The cx88 driver is an example of this: one core v4l2_device struct, but
+  it is used by both an raw video PCI device (cx8800) and a MPEG PCI device
+  (cx8802). Since the v4l2_device cannot be associated with a particular
+  PCI device it is setup without a parent device. But when the struct
+  video_device is setup you do know which parent PCI device to use.
 
 If you use v4l2_ioctl_ops, then you should set either .unlocked_ioctl or
 .ioctl to video_ioctl2 in your v4l2_file_operations struct.