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

On 02.10.20 02:05, Laurent Pinchart wrote:
> 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/

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@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.

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?

>
>> +
>> + /* 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.

Regards,
Stefan

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

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