media: gspca/sn9c20x: Add ability to control built-in webcam LEDs

If you image search "microdia sonix webcam", or SN9C120, you can find
 examples of the type of webcam I have. It has 6 built-in LEDs.
It's ancient (2006 maybe?) but in 2020 it was the only USB webcam I had.
It doesn't perform well, especially in low light.

The Windows XP drivers had the ability to toggle the LEDs, as well as
 "Auto" mode which would read and adjust the exposure and turn them
 on when it got "too dark", along with other nice features, like
 smoothing dead pixels, funky filters, effects and face tracking.

Watching Wireshark usbmon with the Windows driver I was able to discover
 which values are required to toggle the LEDs.

Reading ext-ctrls-flash.rst, V4L2_FLASH_LED_MODE_TORCH seems to describe
 mostly what I want it to do.
Ideally the control would be boolean/checkbox, but the existing
 implementation seems to require a menu.

This patch implements the ability to control the LEDs, attempting to
 minimise changes to external files and other webcams.

Review by anyone more familiar with the code base for unintended
 side effects would be welcome and appreciated. First kernel submission.
Signed-off-by: Pete Hemery <petehemery@hotmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/usb/gspca/sn9c20x.c

@@ -50,6 +50,7 @@ MODULE_LICENSE("GPL");
 #define HAS_NO_BUTTON	0x1
 #define LED_REVERSE	0x2 /* some cameras unset gpio to turn on leds */
 #define FLIP_DETECT	0x4
+#define HAS_LED_TORCH	0x8
 
 /* specific webcam descriptor */
 struct sd {
@@ -77,6 +78,8 @@ struct sd {
 	};
 	struct v4l2_ctrl *jpegqual;
 
+	struct v4l2_ctrl *led_mode;
+
 	struct work_struct work;
 
 	u32 pktsz;			/* (used by pkt_scan) */
@@ -1533,6 +1536,12 @@ static void set_gain(struct gspca_dev *gspca_dev, s32 g)
 	i2c_w(gspca_dev, gain);
 }
 
+static void set_led_mode(struct gspca_dev *gspca_dev, s32 val)
+{
+	reg_w1(gspca_dev, 0x1007, 0x60);
+	reg_w1(gspca_dev, 0x1006, val ? 0x40 : 0x00);
+}
+
 static void set_quality(struct gspca_dev *gspca_dev, s32 val)
 {
 	struct sd *sd = (struct sd *) gspca_dev;
@@ -1699,6 +1708,9 @@ static int sd_s_ctrl(struct v4l2_ctrl *ctrl)
 	case V4L2_CID_JPEG_COMPRESSION_QUALITY:
 		set_quality(gspca_dev, ctrl->val);
 		break;
+	case V4L2_CID_FLASH_LED_MODE:
+		set_led_mode(gspca_dev, ctrl->val);
+		break;
 	}
 	return gspca_dev->usb_err;
 }
@@ -1757,6 +1769,12 @@ static int sd_init_controls(struct gspca_dev *gspca_dev)
 
 	sd->jpegqual = v4l2_ctrl_new_std(hdl, &sd_ctrl_ops,
 			V4L2_CID_JPEG_COMPRESSION_QUALITY, 50, 90, 1, 80);
+
+	if (sd->flags & HAS_LED_TORCH)
+		sd->led_mode = v4l2_ctrl_new_std_menu(hdl, &sd_ctrl_ops,
+				V4L2_CID_FLASH_LED_MODE, V4L2_FLASH_LED_MODE_TORCH,
+				~0x5, V4L2_FLASH_LED_MODE_NONE);
+
 	if (hdl->error) {
 		pr_err("Could not initialize controls\n");
 		return hdl->error;
@@ -2048,6 +2066,8 @@ static int sd_start(struct gspca_dev *gspca_dev)
 		sd->pktsz = sd->npkt = 0;
 		sd->nchg = 0;
 	}
+	if (sd->led_mode)
+		v4l2_ctrl_s_ctrl(sd->led_mode, 0);
 
 	return gspca_dev->usb_err;
 }
@@ -2325,7 +2345,7 @@ static const struct sd_desc sd_desc = {
 
 static const struct usb_device_id device_table[] = {
 	{USB_DEVICE(0x0c45, 0x6240), SN9C20X(MT9M001, 0x5d, 0)},
-	{USB_DEVICE(0x0c45, 0x6242), SN9C20X(MT9M111, 0x5d, 0)},
+	{USB_DEVICE(0x0c45, 0x6242), SN9C20X(MT9M111, 0x5d, HAS_LED_TORCH)},
 	{USB_DEVICE(0x0c45, 0x6248), SN9C20X(OV9655, 0x30, 0)},
 	{USB_DEVICE(0x0c45, 0x624c), SN9C20X(MT9M112, 0x5d, 0)},
 	{USB_DEVICE(0x0c45, 0x624e), SN9C20X(SOI968, 0x30, LED_REVERSE)},