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Subject: Re: [PATCH v2 5/5] media: mt9p031: Fix corrupted frame after
 restarting stream
To:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc:     Mauro Carvalho Chehab <mchehab@kernel.org>,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        Dirk Bender <d.bender@phytec.de>
References: <20200930105133.139981-1-s.riedmueller@phytec.de>
 <20200930105133.139981-5-s.riedmueller@phytec.de>
 <20201002000549.GK3722@pendragon.ideasonboard.com>
From:   =?UTF-8?Q?Stefan_Riedm=c3=bcller?= <s.riedmueller@phytec.de>
Message-ID: <3c8853a6-de34-014d-d10a-d6a55083c4bf@phytec.de>
Date:   Mon, 5 Oct 2020 11:28:21 +0200
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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);
>>   }
>>   
>