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SubjectRe: [PATCH v2 5/5] media: mt9p031: Fix corrupted frame after restarting stream
Hi Stefan,

Thank you for the patch.

On Wed, Sep 30, 2020 at 12:51:33PM +0200, Stefan Riedmueller wrote:
> From: Dirk Bender <d.bender@phytec.de>
>
> To prevent corrupted frames after starting and stopping the sensor it's

s/it's/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>
> ---
> 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.

> #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 ?

> +
> + /* 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.

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

--
Regards,

Laurent Pinchart

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