On Mon December 24 2012 13:27:08 Laurent Pinchart wrote:
> Hi Hans,
>
> On Thursday 27 September 2012 17:16:15 Laurent Pinchart wrote:
> > When one of the requested controls doesn't exist the error_idx field
> > must reflect that situation. For G_EXT_CTRLS and S_EXT_CTRLS, error_idx
> > must be set to the control count. For TRY_EXT_CTRLS, it must be set to
> > the index of the unexisting control.
> >
> > This issue was found by the v4l2-compliance tool.
>
> I'm revisiting this patch as it has been reverted in v3.8-rc1.
>
> > Signed-off-by: Laurent Pinchart <laurent.pinch...@ideasonboard.com>
> > ---
> > drivers/media/usb/uvc/uvc_ctrl.c | 17 ++++++++++-------
> > drivers/media/usb/uvc/uvc_v4l2.c | 19 ++++++++++++-------
> > 2 files changed, 22 insertions(+), 14 deletions(-)
>
> [snip]
>
> > diff --git a/drivers/media/usb/uvc/uvc_v4l2.c
> > b/drivers/media/usb/uvc/uvc_v4l2.c index f00db30..e5817b9 100644
> > --- a/drivers/media/usb/uvc/uvc_v4l2.c
> > +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> > @@ -591,8 +591,10 @@ static long uvc_v4l2_do_ioctl(struct file *file,
>
> [snip]
>
> > @@ -637,8 +639,9 @@ static long uvc_v4l2_do_ioctl(struct file *file,
> > unsigned int cmd, void *arg) ret = uvc_ctrl_get(chain, ctrl);
> > if (ret < 0) {
> > uvc_ctrl_rollback(handle);
> > - ctrls->error_idx = i;
> > - return ret;
> > + ctrls->error_idx = ret == -ENOENT
> > + ? ctrls->count : i;
> > + return ret == -ENOENT ? -EINVAL : ret;
> > }
> > }
> > ctrls->error_idx = 0;
> > @@ -661,8 +664,10 @@ static long uvc_v4l2_do_ioctl(struct file *file,
> > unsigned int cmd, void *arg) ret = uvc_ctrl_set(chain, ctrl);
> > if (ret < 0) {
> > uvc_ctrl_rollback(handle);
> > - ctrls->error_idx = i;
> > - return ret;
> > + ctrls->error_idx = (ret == -ENOENT &&
> > + cmd == VIDIOC_S_EXT_CTRLS)
> > + ? ctrls->count : i;
> > + return ret == -ENOENT ? -EINVAL : ret;
> > }
> > }
>
> I've reread the V4L2 specification, and the least I can say is that the text
> is pretty ambiguous. Let's clarify it.
>
> Is there a reason to differentiate between invalid control IDs and other
> errors as far as error_idx is concerned ? It would be simpler if error_idx
> was
> set to the index of the first error for get and try operations, regardless of
> the error type. What do you think ?
There is a good reason for doing this: the G/S_EXT_CTRLS ioctls have to be as
atomic
as possible, i.e. it should try hard to prevent leaving the hardware in an
inconsistent state because not all controls could be set. It can never be fully
atomic since writing multiple registers over usb or i2c can always return errors
for one of those writes, but it should certainly check for all the obvious
errors first that do not require actually writing to the hardware, such as
whether all the controls in the control list actually exist.
And for such errors error_idx should be set to the number of controls to
indicate that none of the controls were actually set but that there was a
problem with the list of controls itself.
Since TRY_EXT_CTRLS doesn't touch the hardware at all the error_idx can be set
to the index of the control that caused the problem.
The documentation can definitely be improved as the difference between G/S and
TRY with regards to error_idx is not made explicit.
Regards,
Hans
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