Re: [PATCH 20/25] media: ov5647: Program mode only if it has changed

[Dafna Hirschfeld <dafna.hirschfeld@collabora.com>]

On 30.06.20 12:06, Jacopo Mondi wrote:
> Hi Dafna,
> 
> On Tue, Jun 30, 2020 at 11:32:12AM +0200, Dafna Hirschfeld wrote:
>>
>>
>> On 30.06.20 09:43, Jacopo Mondi wrote:
>>> Hi Dafna,
>>>
>>> On Mon, Jun 29, 2020 at 07:48:16PM +0200, Dafna Hirschfeld wrote:
>>>>
>>>>
>>>> On 23.06.20 18:55, Jacopo Mondi wrote:
>>>>> Store in the driver structure a pointer to the currently applied mode
>>>>> and program a new one at s_stream(1) time only if it has changed.
>>>>
>>>> Hi,
>>>> I think this can be more readably implemented with a 'is_streaming' boolean
>>>> field.
>>>
>>> How would you like to use an 'is_streaming' flag to decide if the
>>> sensor mode has to be updated ?
>>
>> since 'current_mode' is set to NULL upon `ov5647_stream_off`
>> and you return from 'ov5647_set_stream' immediately if 'mode == current_mode'
>> it seem very similar to returning immediately from 'ov5647_set_stream' if the
>> device is currently streaming.
> 
> No, the code returns immediately from ov5647_set_mode() if mode ==
> current_mode. The modes comparison makes sure the sensor is not
> reprogrammed if the mode hasn't changed. The remaning part of
> s_stream() is executed regardless of the mode configuration. Am I
> missing some part of the picture ?
> 
>>
>> But actually in this patch it seems to be possible to change the mode
>> while streaming, if the callbacks are executed:
>>
>> s_stream(1)
>> s_fmt
>> s_stream(1)
>>
>> which is maybe a bug?
> 
> The new format is stored in sensor->mode, and applied at the next
> s_stream(1) operation if it differs from the already programmed one,
> at least, this is how it is intended to work, have you found any
> failing s_stream/set_fmt/s_stream which could be caused by a bug ?

What I meant is that there could be valid sequence of calls

s_stream(enable=1)
s_fmt
s_stream(enable=1)

For example if two video devices are connected to the sensor and they
stream simultaneously. There was a discussion about adding a code to the core
to follow the s_stream callback and call it only if the subdev is not streaming
but currently subdevs should support it themselves.


Thanks,
Dafna

> 
> Thanks
>    j
>>
>> Thanks,
>> Dafna
>>
>>>
>>> Thanks
>>>      j
>>>
>>>
>>>>
>>>> Thanks,
>>>> Dafna
>>>>
>>>>>
>>>>> Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
>>>>> ---
>>>>>     drivers/media/i2c/ov5647.c | 16 +++++++++++++++-
>>>>>     1 file changed, 15 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/media/i2c/ov5647.c b/drivers/media/i2c/ov5647.c
>>>>> index 39e320f321bd8..ac114269e1c73 100644
>>>>> --- a/drivers/media/i2c/ov5647.c
>>>>> +++ b/drivers/media/i2c/ov5647.c
>>>>> @@ -96,6 +96,7 @@ struct ov5647 {
>>>>>     	bool				clock_ncont;
>>>>>     	struct v4l2_ctrl_handler	ctrls;
>>>>>     	struct ov5647_mode		*mode;
>>>>> +	struct ov5647_mode		*current_mode;
>>>>>     };
>>>>>     static inline struct ov5647 *to_sensor(struct v4l2_subdev *sd)
>>>>> @@ -750,9 +751,13 @@ static int ov5647_set_virtual_channel(struct v4l2_subdev *sd, int channel)
>>>>>     static int ov5647_set_mode(struct v4l2_subdev *sd)
>>>>>     {
>>>>>     	struct i2c_client *client = v4l2_get_subdevdata(sd);
>>>>> +	struct ov5647 *sensor = to_sensor(sd);
>>>>>     	u8 resetval, rdval;
>>>>>     	int ret;
>>>>> +	if (sensor->mode == sensor->current_mode)
>>>>> +		return 0;
>>>>> +
>>>>>     	ret = ov5647_read(sd, OV5647_SW_STANDBY, &rdval);
>>>>>     	if (ret < 0)
>>>>>     		return ret;
>>>>> @@ -778,6 +783,8 @@ static int ov5647_set_mode(struct v4l2_subdev *sd)
>>>>>     			return ret;
>>>>>     	}
>>>>> +	sensor->current_mode = sensor->mode;
>>>>> +
>>>>>     	return 0;
>>>>>     }
>>>>> @@ -816,6 +823,7 @@ static int ov5647_stream_on(struct v4l2_subdev *sd)
>>>>>     static int ov5647_stream_off(struct v4l2_subdev *sd)
>>>>>     {
>>>>> +	struct ov5647 *sensor = to_sensor(sd);
>>>>>     	int ret;
>>>>>     	ret = ov5647_write(sd, OV5647_REG_MIPI_CTRL00, MIPI_CTRL00_CLOCK_LANE_GATE |
>>>>> @@ -827,7 +835,13 @@ static int ov5647_stream_off(struct v4l2_subdev *sd)
>>>>>     	if (ret < 0)
>>>>>     		return ret;
>>>>> -	return ov5647_write(sd, OV5640_REG_PAD_OUT, 0x01);
>>>>> +	ret = ov5647_write(sd, OV5640_REG_PAD_OUT, 0x01);
>>>>> +	if (ret < 0)
>>>>> +		return ret;
>>>>> +
>>>>> +	sensor->current_mode = NULL;
>>>>> +
>>>>> +	return 0;
>>>>>     }
>>>>>     static int set_sw_standby(struct v4l2_subdev *sd, bool standby)
>>>>>