Em Wed, 10 Jun 2009 22:39:51 -0300
Mauro Carvalho Chehab <mchehab@xxxxxxxxxx> escreveu:
> Em Sun, 31 May 2009 14:41:52 +0800
> "Figo.zhang" <figo1802@xxxxxxxxx> escreveu:
>
> > video_register_device() return zero on success, it would not return a positive integer.
> >
> > Signed-off-by: Figo.zhang <figo1802@xxxxxxxxx>
> > ---
> > drivers/media/video/ov511.c | 2 +-
> > 1 files changed, 1 insertions(+), 1 deletions(-)
> >
> > diff --git a/drivers/media/video/ov511.c b/drivers/media/video/ov511.c
> > index 9af5532..816427e 100644
> > --- a/drivers/media/video/ov511.c
> > +++ b/drivers/media/video/ov511.c
> > @@ -5851,7 +5851,7 @@ ov51x_probe(struct usb_interface *intf, const struct usb_device_id *id)
> > break;
> >
> > if (video_register_device(ov->vdev, VFL_TYPE_GRABBER,
> > - unit_video[i]) >= 0) {
> > + unit_video[i]) == 0) {
> > break;
> > }
> > }
>
> Nack.
>
> Errors are always negative. So, any zero or positive value indicates that no error occurred.
>
> Yet, the logic for forcing ov51x to specific minor number seems broken: it will
> end by registering the device twice, if used.
>
> So, that part of the function needs a rewrite. I'll fix it.
>
Hmm... the issue seems more complex than I've imagined...
When ov511 were written, it was assumed that video_register_device(dev, v, nr)
would have the following behavior:
if nr = -1, it would do dynamic minor allocation;
if nr >= 0, it would allocate to 'nr' minor or fail.
With the original behavior.
The ov511_probe registering loop is doing something like this (I did a cleanup
to allow a better understand of the logic):
<snip>
#define OV511_MAX_UNIT_VIDEO 16
...
static int unit_video[OV511_MAX_UNIT_VIDEO];
...
module_param_array(unit_video, int, &num_uv, 0);
MODULE_PARM_DESC(unit_video,
"Force use of specific minor number(s). 0 is not allowed.");
...
static int
ov51x_probe(struct usb_interface *intf, const struct usb_device_id *id)
{
...
for (i = 0; i < OV511_MAX_UNIT_VIDEO; i++) {
/* Minor 0 cannot be specified; assume user wants autodetect */
if (unit_video[i] == 0)
break;
if (video_register_device(ov->vdev, VFL_TYPE_GRABBER,
unit_video[i]) >= 0)
goto register_succeded;
}
/* Use the next available one */
if (video_register_device(ov->vdev, VFL_TYPE_GRABBER, -1) < 0) {
err("video_register_device failed");
goto error;
register_succeeded:
dev_info(&intf->dev, "Device at %s registered to minor %d\n",
ov->usb_path, ov->vdev->minor);
</snip>
So, if you probe ov511 with a list of device numbers, for example:
modprobe ov511 4,1,3
And assuming that you have 5 ov511 devices, and connect they one by one,
they'll gain the following device numbers (at the connection order):
/dev/video4
/dev/video1
/dev/video3
/dev/video0
/dev/video2
However, changeset 9133:
changeset: 9133:64aed7485a43
parent: 9073:4db9722caf4f
user: Hans Verkuil <hverkuil@xxxxxxxxx>
date: Sat Oct 04 13:36:54 2008 +0200
summary: v4l: disconnect kernel number from minor
Changed the behavior video_register_device(dev, v, nr):
+ nr = find_next_zero_bit(video_nums[type], minor_cnt, nr == -1 ? 0 : nr);
So, instead of accepting just -1 or nr, it will now do:
if nr = -1, it will do dynamic minor allocation (as before);
if nr >= 0, it will also do dynamic minor allocation, but starting from nr.
So, the new code won't fail if nr is already allocated, but it will return the
next unallocated nr.
With the ov511 code, this means that you'll have, instead:
/dev/video5
/dev/video6
/dev/video7
/dev/video8
/dev/video9
So, changeset 9133 actually broke the ov511 probe original behavior.
In order to restore the original behavior, the probe logic should be replaced
by something else (like the approach taken by em28xx).
Also, changeset 9133 may also cause other side effects on other drivers that
were expecting the original behavior.
To make things worse, the function comment doesn't properly explain the current
behavior.
---
Figo,
Since we are in the middle of a merge window, it is unlikely that I'll have
enough time to properly fix it right now (since my priority right now is to
merge the existing patches).
As you started proposing a patch for it, maybe you could try to fix it and
check about similar troubles on other drivers.
Cheers,
Mauro
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