Add support for Logitech PTZ Pro 2 to webcam_private api.

The camera supports absolute positioning via an extension unit (as opposed to the camera terminal unit as many other cameras do). So before issuing a v4l2 command to do absolute positioning we map the command to that extension unit. In case the camera does not implement that extension unit (e.g. all non-logitech cameras) this mapping just silently fails.

BUG: 826296
Change-Id: I939de844375efc6b8a756efe0877cb4bf0dc9a56
Reviewed-on: https://chromium-review.googlesource.com/982056
Commit-Queue: Daniel Fenner <dfenner@google.com>
Reviewed-by: Zachary Kuznia <zork@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548398}

extensions/browser/api/webcam_private/v4l2_webcam.cc

@@ -35,17 +35,40 @@ const uvc_menu_info kLogitechCmdMenu[] = {
 };
 
 const uvc_xu_control_mapping kLogitechCmdMapping = {
-  V4L2_CID_PANTILT_CMD,
-  "Pan/Tilt Go",
-  UVC_GUID_LOGITECH_CC3000E_MOTORS,
-  LOGITECH_MOTORCONTROL_PANTILT_CMD,
-  8,
-  0,
-  V4L2_CTRL_TYPE_MENU,
-  UVC_CTRL_DATA_TYPE_ENUM,
-  const_cast<uvc_menu_info*>(&kLogitechCmdMenu[0]),
-  arraysize(kLogitechCmdMenu),
+    V4L2_CID_PANTILT_CMD,
+    "Pan/Tilt Go",
+    UVC_GUID_LOGITECH_CC3000E_MOTORS,
+    LOGITECH_MOTORCONTROL_PANTILT_CMD,
+    8,
+    0,
+    V4L2_CTRL_TYPE_MENU,
+    UVC_CTRL_DATA_TYPE_ENUM,
+    const_cast<uvc_menu_info*>(&kLogitechCmdMenu[0]),
+    arraysize(kLogitechCmdMenu),
 };
+
+const uvc_xu_control_mapping kLogitechPanAbsoluteMapping = {
+    V4L2_CID_PAN_ABSOLUTE,
+    "Pan (Absolute)",
+    UVC_GUID_LOGITECH_CC3000E_MOTORS,
+    12,
+    32,
+    0,
+    V4L2_CTRL_TYPE_INTEGER,
+    UVC_CTRL_DATA_TYPE_SIGNED,
+};
+
+const uvc_xu_control_mapping kLogitechTiltAbsoluteMapping = {
+    V4L2_CID_TILT_ABSOLUTE,
+    "Tilt (Absolute)",
+    UVC_GUID_LOGITECH_CC3000E_MOTORS,
+    12,
+    32,
+    32,
+    V4L2_CTRL_TYPE_INTEGER,
+    UVC_CTRL_DATA_TYPE_SIGNED,
+};
+
 }  // namespace
 
 namespace extensions {
@@ -72,6 +95,15 @@ bool V4L2Webcam::EnsureLogitechCommandsMapped() {
 }
 
 bool V4L2Webcam::SetWebcamParameter(int fd, uint32_t control_id, int value) {
+  // Try to map the V4L2 control to the Logitech extension unit. If the
+  // connected camera does not implement these extension unit this will just
+  // silently fail and the standard camera terminal controls will be used.
+  if (control_id == V4L2_CID_PAN_ABSOLUTE) {
+    HANDLE_EINTR(ioctl(fd, UVCIOC_CTRL_MAP, &kLogitechPanAbsoluteMapping));
+  } else if (control_id == V4L2_CID_TILT_ABSOLUTE) {
+    HANDLE_EINTR(ioctl(fd, UVCIOC_CTRL_MAP, &kLogitechTiltAbsoluteMapping));
+  }
+
   struct v4l2_control v4l2_ctrl = {control_id, value};
   int res = HANDLE_EINTR(ioctl(fd, VIDIOC_S_CTRL, &v4l2_ctrl)) >= 0;
   return res >= 0;