V4L/DVB (12411): em28xx: Fix artifacts with Silvercrest webcam

Silvercrest mt9v011 sensor produces a 640x480 image. However,
previously, the code were getting only half of the lines and merging two
consecutive frames to "produce" a 640x480 image.

With the addition of progressive mode, now em28xx is working with a full
image. However, when the number of lines is bigger than 240, the
beginning of some odd lines are filled with blank.

After lots of testing, and physically checking the device for a Xtal, it
was noticed experimentally that mt9v011 is using em28xx XCLK as its
clock. Due to that, changing XCLK value changes the maximum speed of the
stream.

At the tests, it were possible to produce up to 32 fps, using a 30 MHz
XCLK. However, at that rate, the artifacts happen even at 320x240. Lower
values of XCLK produces artifacts only at 640x480.

At some values of xclk (for example XCLKK = 6 MHz, 640x480), it is
possible to see an invalid sucession of artifacts with this pattern:

.xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
..xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
...xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
....xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
.xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
..xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
...xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
....xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

(where the dots represent the blanked pixels)

So, it seems that a waveform in the format of a ramp is interferring at
the image.

The cause of this interference is currently unknown. Some possibilities
are:
	- electrical interference (maybe this device is broken?);
	- some issue at mt9v011 programming;
	- some bug at em28xx chip.

So, for now, let's be conservative and use a value of XCLK that we know
for sure that it won't cause artifacts.

As I'm waiting for more of such devices with different em28xx chipset
revisions, I'll have the opportunity to double check the issue with
other pieces of hardware.

Later patches can vary XCLK depending on the vertical resolutions, if a
proper fix is not discovered.
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/em28xx/em28xx-cards.c

@@ -218,7 +218,7 @@ static struct em28xx_reg_seq silvercrest_reg_seq[] = {
 struct em28xx_board em28xx_boards[] = {
 	[EM2750_BOARD_UNKNOWN] = {
 		.name          = "EM2710/EM2750/EM2751 webcam grabber",
-		.xclk          = EM28XX_XCLK_FREQUENCY_48MHZ,
+		.xclk          = EM28XX_XCLK_FREQUENCY_20MHZ,
 		.tuner_type    = TUNER_ABSENT,
 		.is_webcam     = 1,
 		.input         = { {
@@ -1768,6 +1768,7 @@ static int em28xx_hint_sensor(struct em28xx *dev)
 	__be16 version_be;
 	u16 version;
 
+	/* Micron sensor detection */
 	dev->i2c_client.addr = 0xba >> 1;
 	cmd = 0;
 	i2c_master_send(&dev->i2c_client, &cmd, 1);
@@ -1776,16 +1777,27 @@ static int em28xx_hint_sensor(struct em28xx *dev)
 		return -EINVAL;
 
 	version = be16_to_cpu(version_be);
-
 	switch (version) {
 	case 0x8232:		/* mt9v011 640x480 1.3 Mpix sensor */
 	case 0x8243:		/* mt9v011 rev B 640x480 1.3 Mpix sensor */
 		dev->model = EM2820_BOARD_SILVERCREST_WEBCAM;
+		em28xx_set_model(dev);
+
 		sensor_name = "mt9v011";
 		dev->em28xx_sensor = EM28XX_MT9V011;
 		dev->sensor_xres = 640;
 		dev->sensor_yres = 480;
-		dev->sensor_xtal = 12150000;
+		/*
+		 * FIXME: mt9v011 uses I2S speed as xtal clk - at least with
+		 * the Silvercrest cam I have here for testing - for higher
+		 * resolutions, a high clock cause horizontal artifacts, so we
+		 * need to use a lower xclk frequency.
+		 * Yet, it would be possible to adjust xclk depending on the
+		 * desired resolution, since this affects directly the
+		 * frame rate.
+		 */
+		dev->board.xclk = EM28XX_XCLK_FREQUENCY_4_3MHZ;
+		dev->sensor_xtal = 4300000;
 
 		/* probably means GRGB 16 bit bayer */
 		dev->vinmode = 0x0d;
@@ -1794,6 +1806,8 @@ static int em28xx_hint_sensor(struct em28xx *dev)
 		break;
 	case 0x8431:
 		dev->model = EM2750_BOARD_UNKNOWN;
+		em28xx_set_model(dev);
+
 		sensor_name = "mt9m001";
 		dev->em28xx_sensor = EM28XX_MT9M001;
 		em28xx_initialize_mt9m001(dev);
@@ -1810,6 +1824,9 @@ static int em28xx_hint_sensor(struct em28xx *dev)
 		return -EINVAL;
 	}
 
+	/* Setup webcam defaults */
+	em28xx_pre_card_setup(dev);
+
 	em28xx_errdev("Sensor is %s, using model %s entry.\n",
 		      sensor_name, em28xx_boards[dev->model].name);
 
@@ -2169,7 +2186,20 @@ void em28xx_register_i2c_ir(struct em28xx *dev)
 
 void em28xx_card_setup(struct em28xx *dev)
 {
-	em28xx_set_model(dev);
+	/*
+	 * If the device can be a webcam, seek for a sensor.
+	 * If sensor is not found, then it isn't a webcam.
+	 */
+	if (dev->board.is_webcam) {
+		if (em28xx_hint_sensor(dev) < 0)
+			dev->board.is_webcam = 0;
+		else
+			dev->progressive = 1;
+	} else
+		em28xx_set_model(dev);
+
+	em28xx_info("Identified as %s (card=%d)\n",
+		    dev->board.name, dev->model);
 
 	dev->tuner_type = em28xx_boards[dev->model].tuner_type;
 	if (em28xx_boards[dev->model].tuner_addr)
@@ -2489,18 +2519,6 @@ static int em28xx_init_dev(struct em28xx **devhandle, struct usb_device *udev,
 	dev->vinmode = 0x10;
 	dev->vinctl  = 0x11;
 
-	/*
-	 * If the device can be a webcam, seek for a sensor.
-	 * If sensor is not found, then it isn't a webcam.
-	 */
-	if (dev->board.is_webcam)
-		if (em28xx_hint_sensor(dev) < 0)
-			dev->board.is_webcam = 0;
-
-	/* It makes no sense to use de-interlacing mode on webcams */
-	if (dev->board.is_webcam)
-		dev->progressive = 1;
-
 	/* Do board specific init and eeprom reading */
 	em28xx_card_setup(dev);