[PATCH v2 5/5] media: mt9p031: Fix corrupted frame after restarting stream

[Stefan Riedmueller]

From: Dirk Bender <d.ben...@phytec.de>

To prevent corrupted frames after starting and stopping the sensor it's
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.ben...@phytec.de>
Signed-off-by: Stefan Riedmueller <s.riedmuel...@phytec.de>
---
No changes in v2
---
 drivers/media/i2c/mt9p031.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/drivers/media/i2c/mt9p031.c b/drivers/media/i2c/mt9p031.c
index d10457361e6c..d59f66e3dcf3 100644
--- a/drivers/media/i2c/mt9p031.c
+++ b/drivers/media/i2c/mt9p031.c
@@ -80,6 +80,8 @@
 #define                MT9P031_PIXEL_CLOCK_SHIFT(n)            ((n) << 8)
 #define                MT9P031_PIXEL_CLOCK_DIVIDE(n)           ((n) << 0)
 #define MT9P031_FRAME_RESTART                          0x0b
+#define                MT9P031_FRAME_RESTART_SET               (1 << 0)
+#define                MT9P031_FRAME_PAUSE_RESTART_SET         (1 << 1)
 #define MT9P031_SHUTTER_DELAY                          0x0c
 #define MT9P031_RST                                    0x0d
 #define                MT9P031_RST_ENABLE                      1
@@ -483,9 +485,25 @@ 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) {
+               val = mt9p031_read(client, MT9P031_FRAME_RESTART);
+
+               /* enable pause restart */
+               val |= MT9P031_FRAME_PAUSE_RESTART_SET;
+               ret = mt9p031_write(client, MT9P031_FRAME_RESTART, val);
+               if (ret < 0)
+                       return ret;
+
+               /* enable restart + keep pause restart set */
+               val |= MT9P031_FRAME_RESTART_SET;
+               ret = mt9p031_write(client, MT9P031_FRAME_RESTART, val);
+               if (ret < 0)
+                       return ret;
+
                /* Stop sensor readout */
                ret = mt9p031_set_output_control(mt9p031,
                                                 MT9P031_OUTPUT_CONTROL_CEN, 0);
@@ -505,6 +523,13 @@ static int mt9p031_s_stream(struct v4l2_subdev *subdev, 
int enable)
        if (ret < 0)
                return ret;
 
+       val = mt9p031_read(client, MT9P031_FRAME_RESTART);
+       /* disable reset + pause restart */
+       val &= ~MT9P031_FRAME_PAUSE_RESTART_SET;
+       ret = mt9p031_write(client, MT9P031_FRAME_RESTART, val);
+       if (ret < 0)
+               return ret;
+
        return mt9p031_pll_enable(mt9p031);
 }
 
-- 
2.25.1