media: mt9p031: Fix corrupted frame after restarting stream

To prevent corrupted frames after starting and stopping the sensor its
datasheet specifies a specific pause sequence to follow:

Stopping:
	Set Pause_Restart Bit -> Set Restart Bit -> Set Chip_Enable Off

Restarting:
	Set Chip_Enable On -> Clear Pause_Restart Bit

The Restart Bit is cleared automatically and must not be cleared
manually as this would cause undefined behavior.

Signed-off-by: Dirk Bender <d.bender@phytec.de>
Signed-off-by: Stefan Riedmueller <s.riedmueller@phytec.de>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

diff --git a/drivers/media/i2c/mt9p031.c b/drivers/media/i2c/mt9p031.c
index ea90aff..ee27770 100644 (file)
--- a/drivers/media/i2c/mt9p031.c
+++ b/drivers/media/i2c/mt9p031.c
@@ -79,7 +79,9 @@
 #define                MT9P031_PIXEL_CLOCK_INVERT              (1 << 15)
 #define                MT9P031_PIXEL_CLOCK_SHIFT(n)            ((n) << 8)
 #define                MT9P031_PIXEL_CLOCK_DIVIDE(n)           ((n) << 0)
-#define MT9P031_FRAME_RESTART                          0x0b
+#define MT9P031_RESTART                                        0x0b
+#define                MT9P031_FRAME_PAUSE_RESTART             (1 << 1)
+#define                MT9P031_FRAME_RESTART                   (1 << 0)
 #define MT9P031_SHUTTER_DELAY                          0x0c
 #define MT9P031_RST                                    0x0d
 #define                MT9P031_RST_ENABLE                      1
@@ -456,9 +458,23 @@ static int mt9p031_set_params(struct mt9p031 *mt9p031)
 static int mt9p031_s_stream(struct v4l2_subdev *subdev, int enable)
 {
        struct mt9p031 *mt9p031 = to_mt9p031(subdev);
+       struct i2c_client *client = v4l2_get_subdevdata(subdev);
+       int val;
        int ret;
 
        if (!enable) {
+               /* enable pause restart */
+               val = MT9P031_FRAME_PAUSE_RESTART;
+               ret = mt9p031_write(client, MT9P031_RESTART, val);
+               if (ret < 0)
+                       return ret;
+
+               /* enable restart + keep pause restart set */
+               val |= MT9P031_FRAME_RESTART;
+               ret = mt9p031_write(client, MT9P031_RESTART, val);
+               if (ret < 0)
+                       return ret;
+
                /* Stop sensor readout */
                ret = mt9p031_set_output_control(mt9p031,
                                                 MT9P031_OUTPUT_CONTROL_CEN, 0);
@@ -478,6 +494,16 @@ static int mt9p031_s_stream(struct v4l2_subdev *subdev, int enable)
        if (ret < 0)
                return ret;
 
+       /*
+        * - clear pause restart
+        * - don't clear restart as clearing restart manually can cause
+        *   undefined behavior
+        */
+       val = MT9P031_FRAME_RESTART;
+       ret = mt9p031_write(client, MT9P031_RESTART, val);
+       if (ret < 0)
+               return ret;
+
        return mt9p031_pll_enable(mt9p031);
 }