[PATCH v2] media: uvcvideo: Filter hw errors while enumerating controls

[Ricardo Ribalda <ribalda@chromium.org>]

To implement VIDIOC_QUERYCTRL, we need to know the minimum, maximum,
step and flags of the control. For some of the controls, this involves
querying the actual hardware.

Some non-compliant cameras produce errors when we query them. Right now,
we populate that error to userspace. When an error happens, the v4l2
framework does not copy the v4l2_queryctrl struct to userspace. Also,
userspace apps are not ready to handle any other error than -EINVAL.

One of the main usecases of VIDIOC_QUERYCTRL is enumerating the controls
of a device. This is done using the V4L2_CTRL_FLAG_NEXT_CTRL flag. In
that usecase, a non-compliant control will make it almost impossible to
enumerate all controls of the device.

A control with an invalid max/min/step/flags is better than non being
able to enumerate the rest of the controls.

This patch makes VIDIOC_QUERYCTRL return 0 in all the error cases
different than -EINVAL and introduces a warning in dmesg so we can
have a trace of what has happened.

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
Hi 2*Hans and Laurent!

I came around a device that was listing just a couple of controls when
it should be listing much more.

Some debugging latter I found that the device was returning -EIO when
all the focal controls were read.

Lots of good arguments in favor/against this patch in the v1. Please
check!

Without this patch:
$ v4l2-ctl --list-ctrls
                  auto_exposure 0x009a0901 (menu)   : min=0 max=3 default=3 value=3 (Aperture Priority Mode)
         exposure_time_absolute 0x009a0902 (int)    : min=50 max=10000 step=1 default=166 value=166 flags=inactive
     exposure_dynamic_framerate 0x009a0903 (bool)   : default=0 value=0
region_of_interest_auto_control 0x009a1902 (bitmask): max=0x00000001 default=0x00000001 value=1

With this patch:
$ v4l2-ctl --list-ctrls
                  auto_exposure 0x009a0901 (menu)   : min=0 max=3 default=3 value=3 (Aperture Priority Mode)
         exposure_time_absolute 0x009a0902 (int)    : min=50 max=10000 step=1 default=166 value=166 flags=inactive
     exposure_dynamic_framerate 0x009a0903 (bool)   : default=0 value=0
error 5 getting ext_ctrl Focus, Absolute
error 5 getting ext_ctrl Focus, Automatic Continuous
   region_of_interest_rectangle 0x009a1901 (unknown): type=107 value=unsupported payload type flags=has-payload
region_of_interest_auto_control 0x009a1902 (bitmask): max=0x00000001 default=0x00000001 value=1

--
---
Changes in v2:
- Never return error, even if we are not enumerating the controls
- Improve commit message.
- Link to v1: https://lore.kernel.org/r/20241213-uvc-eaccess-v1-1-62e0b4fcc634@chromium.org
---
 drivers/media/usb/uvc/uvc_ctrl.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
index 4e58476d305e..43ddc5bb02db 100644
--- a/drivers/media/usb/uvc/uvc_ctrl.c
+++ b/drivers/media/usb/uvc/uvc_ctrl.c
@@ -1307,17 +1307,24 @@ static int __uvc_query_v4l2_ctrl(struct uvc_video_chain *chain,
 	if (master_ctrl && (master_ctrl->info.flags & UVC_CTRL_FLAG_GET_CUR)) {
 		s32 val;
 		int ret = __uvc_ctrl_get(chain, master_ctrl, master_map, &val);
-		if (ret < 0)
-			return ret;
 
-		if (val != mapping->master_manual)
-				v4l2_ctrl->flags |= V4L2_CTRL_FLAG_INACTIVE;
+		if (ret < 0) {
+			dev_warn_ratelimited(&chain->dev->udev->dev,
+					     "UVC non compliance: Error %d querying master control %x\n",
+					      ret, master_map->id);
+		} else if (val != mapping->master_manual) {
+			v4l2_ctrl->flags |= V4L2_CTRL_FLAG_INACTIVE;
+		}
 	}
 
 	if (!ctrl->cached) {
 		int ret = uvc_ctrl_populate_cache(chain, ctrl);
-		if (ret < 0)
-			return ret;
+
+		if (ret < 0) {
+			dev_warn_ratelimited(&chain->dev->udev->dev,
+					     "UVC non compliance: Error %d populating cache of control %x\n",
+					     ret, mapping->id);
+		}
 	}
 
 	if (ctrl->info.flags & UVC_CTRL_FLAG_GET_DEF) {

---
base-commit: 40ed9e9b2808beeb835bd0ed971fb364c285d39c
change-id: 20241213-uvc-eaccess-755cc061a360

Best regards,
-- 
Ricardo Ribalda <ribalda@chromium.org>