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Subject[PATCH v3 5/6] media: mt9p031: Fix corrupted frame after restarting stream
Date
From: Dirk Bender <d.bender@phytec.de>

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>
---
drivers/media/i2c/mt9p031.c | 28 +++++++++++++++++++++++++++-
1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/drivers/media/i2c/mt9p031.c b/drivers/media/i2c/mt9p031.c
index 6a6f16df3f4a..3511c4ff350d 100644
--- 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
@@ -482,9 +484,23 @@ 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);
@@ -504,6 +520,16 @@ 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);
}

--
2.25.1
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