Re: [PATCH] uvcvideo: uvc_ctrl_is_accessible: check for INACTIVE

[Hans Verkuil <hverkuil@xs4all.nl>]

On 23/03/2021 16:29, Ricardo Ribalda Delgado wrote:
> Hi Hans
> 
> On Mon, Mar 22, 2021 at 1:06 PM Hans Verkuil <hverkuil@xs4all.nl> wrote:
>>
>> Check for inactive controls in uvc_ctrl_is_accessible().
>> Use the new value for the master_id controls if present,
>> otherwise use the existing value to determine if it is OK
>> to set the control. Doing this here avoids attempting to
>> set an inactive control, which will return an error from the
>> USB device.
> 
> Dont you think that this patch is not needed if this is used:
> https://patchwork.linuxtv.org/project/linux-media/patch/20210319170906.278238-17-ribalda@chromium.org/
> ?

That might well be the case :-)

I haven't really looked at that.

> 
> 
> Also Maybe it is wrong. (Maybe it is the keyword here ;).
> I think the initial assumption was that uvc_ctrl_is_accessible shall
> not access the hardware, but with this patch it is accessing it.

It's only accessing it if master_ctrl->loaded is 0 (see __uvc_ctrl_get()).
If loaded is 0, and __uvc_ctrl_get() returns an error, then that error is
ignored and the code will assume that the control is accessible.

Note that what we try to avoid is *setting* an inactive control. In this
case we're reading the master control, which should be safe except for
USB hardware problems that can return an error.

Regards,

	Hans

>>
>> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
>> ---
>> Ricardo: this can be added to your uvc series. It avoids attempts to set
>> inactive controls.
>> ---
>>  drivers/media/usb/uvc/uvc_ctrl.c | 28 +++++++++++++++++++++++++++-
>>  drivers/media/usb/uvc/uvc_v4l2.c |  4 ++--
>>  drivers/media/usb/uvc/uvcvideo.h |  3 ++-
>>  3 files changed, 31 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
>> index d9d4add1e813..6e7b904bc33d 100644
>> --- a/drivers/media/usb/uvc/uvc_ctrl.c
>> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
>> @@ -1047,10 +1047,18 @@ static int uvc_query_v4l2_class(struct uvc_video_chain *chain, u32 req_id,
>>  }
>>
>>  int uvc_ctrl_is_accessible(struct uvc_video_chain *chain, u32 v4l2_id,
>> -                          bool read)
>> +                          const struct v4l2_ext_controls *ctrls,
>> +                          unsigned long ioctl)
>>  {
>> +       struct uvc_control_mapping *master_map = NULL;
>> +       struct uvc_control *master_ctrl = NULL;
>>         struct uvc_control_mapping *mapping;
>>         struct uvc_control *ctrl;
>> +       bool read = ioctl == VIDIOC_G_EXT_CTRLS;
>> +       bool try = ioctl == VIDIOC_TRY_EXT_CTRLS;
>> +       s32 val;
>> +       int ret;
>> +       int i;
>>
>>         if (__uvc_query_v4l2_class(chain, v4l2_id, 0) >= 0)
>>                 return -EACCES;
>> @@ -1065,6 +1073,24 @@ int uvc_ctrl_is_accessible(struct uvc_video_chain *chain, u32 v4l2_id,
>>         if (!(ctrl->info.flags & UVC_CTRL_FLAG_SET_CUR) && !read)
>>                 return -EACCES;
>>
>> +       if (read || try || !mapping->master_id)
>> +               return 0;
>> +
>> +       for (i = ctrls->count - 1; i >= 0; i--)
>> +               if (ctrls->controls[i].id == mapping->master_id)
>> +                       return ctrls->controls[i].value ==
>> +                                       mapping->master_manual ? 0 : -EACCES;
>> +
>> +       __uvc_find_control(ctrl->entity, mapping->master_id, &master_map,
>> +                          &master_ctrl, 0);
>> +
>> +       if (!master_ctrl || !(master_ctrl->info.flags & UVC_CTRL_FLAG_GET_CUR))
>> +               return 0;
>> +
>> +       ret = __uvc_ctrl_get(chain, master_ctrl, master_map, &val);
>> +       if (ret >= 0 && val != mapping->master_manual)
>> +               return -EACCES;
>> +
>>         return 0;
>>  }
>>
>> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
>> index 12362e0f9870..e40db7ae18b1 100644
>> --- a/drivers/media/usb/uvc/uvc_v4l2.c
>> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
>> @@ -803,8 +803,8 @@ static int uvc_ctrl_check_access(struct uvc_video_chain *chain,
>>         int ret = 0;
>>
>>         for (i = 0; i < ctrls->count; ++ctrl, ++i) {
>> -               ret = uvc_ctrl_is_accessible(chain, ctrl->id,
>> -                                           ioctl == VIDIOC_G_EXT_CTRLS);
>> +               ret = uvc_ctrl_is_accessible(chain, ctrl->id, ctrls,
>> +                                           ioctl);
>>                 if (ret)
>>                         break;
>>         }
>> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
>> index aedb4d3d4db9..8849d7953767 100644
>> --- a/drivers/media/usb/uvc/uvcvideo.h
>> +++ b/drivers/media/usb/uvc/uvcvideo.h
>> @@ -869,7 +869,8 @@ static inline int uvc_ctrl_rollback(struct uvc_fh *handle)
>>  int uvc_ctrl_get(struct uvc_video_chain *chain, struct v4l2_ext_control *xctrl);
>>  int uvc_ctrl_set(struct uvc_fh *handle, struct v4l2_ext_control *xctrl);
>>  int uvc_ctrl_is_accessible(struct uvc_video_chain *chain, u32 v4l2_id,
>> -                          bool read);
>> +                          const struct v4l2_ext_controls *ctrls,
>> +                          unsigned long ioctl);
>>
>>  int uvc_xu_ctrl_query(struct uvc_video_chain *chain,
>>                       struct uvc_xu_control_query *xqry);
>> --
>> 2.30.0
>>
>>
> 
>