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

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Hi Laurent,

On 05.10.20 15:08, Laurent Pinchart wrote:
Hi Stefan,

On Mon, Oct 05, 2020 at 11:28:21AM +0200, Stefan Riedmüller wrote:
On 02.10.20 02:05, Laurent Pinchart wrote:
On Wed, Sep 30, 2020 at 12:51:33PM +0200, Stefan Riedmueller wrote:
From: Dirk Bender <d.bender@xxxxxxxxx>

To prevent corrupted frames after starting and stopping the sensor it's

s/it's/its/

thanks, I'll fix that.

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@xxxxxxxxx>
Signed-off-by: Stefan Riedmueller <s.riedmueller@xxxxxxxxx>
---
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)

The fields are named Restart and Pause_Restart, I would drop _SET. Could
you also sort them from MSB to LSB as for the other registers ? Using
BIT() would be good too, although this could be done as an additional
patch to convert all the existing macros.

I'll do that. Also I will rename the register to MT9P031_RESTART and the
bits to MT9P031_FRAME_RESTART and MT9P031_FRAME_PAUSE_RESTART.

   #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);

Do you need to read the register ? Can't you write
MT9P031_FRAME_PAUSE_RESTART_SET and then MT9P031_FRAME_PAUSE_RESTART_SET
| MT9P031_FRAME_RESTART_SET ? And actually, can't we just write both
bits in one go, do we need two writes ?

I think you're right we don't necessarily need to read the registers. The
only other bit is not used by the driver.

But I think we do need two separate writes, at least that is what the
datasheet states.

So I would drop the read but keep both write, ok?

That's fine with me if required, although I don't see where this is
indicated in the datasheet, but I may have missed it.

It's in "Standby and Chip Enable". There is a Sequence for entering soft standby with two separate writes:

REG = 0x0B, 0x0002
REG = 0x0B, 0x0003

Regards,
Stefan


+
+		/* 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;

Same here, I think you can simply write MT9P031_FRAME_PAUSE_RESTART_SET.

I'll drop the read here as well. But I need to make sure, that the Restart
Bit is not cleared manually here.

+	ret = mt9p031_write(client, MT9P031_FRAME_RESTART, val);
+	if (ret < 0)
+		return ret;
+
   	return mt9p031_pll_enable(mt9p031);
   }





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