[Linux-stm32] [PATCH v2] media: ov5640: add support of V4L2_CID_LINK_FREQ

[Hugues FRUCHET]

Hi Sakari,

On 6/27/19 6:05 PM, Sakari Ailus wrote:
> Hi Hugues,
> 
> On Thu, Jun 27, 2019 at 02:57:04PM +0200, Hugues Fruchet wrote:
>> Add support of V4L2_CID_LINK_FREQ, this is needed
>> by some CSI-2 receivers.
>>
>> 384MHz is exposed for the time being, corresponding
>> to 96MHz pixel clock with 2 bytes per pixel on 2 data lanes.
>>
>> This setup has been tested successfully with ST MIPID02
>> CSI-2 to parallel bridge.
>>
>> Signed-off-by: Hugues Fruchet <hugues.fruchet at st.com>
>> ---
> 
> Thanks for the patch.
> 
> The driver calculates the sensor configuration based on its configuration,
> and this needs to be reflected in the link frequency: it's not a static
> value. See e.g. ov5640_calc_sys_clk().
> 

I know this code, but for a reason I don't understand yet, this seems
to not have effects on the CSI-2 link frequency.

This has been verified with MIPID02 CSI-2 bridge which only work with
this fixed link frequency as input to program its ui_x4 register 
setting, see 
https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg2028171.html.
All resolutions and all framerate have been tested succesfully with this 
setting.

Initially I tried to set the link frequency according to the value 
computed in ov5640_calc_sys_clk() but it was only functional when 
resolutions/framerate was close to the 384MHz value...

As OV5640 D3 engineering board has been initially developped for 
dragonboard, I'll dig into this and found this commit:
https://lore.kernel.org/patchwork/patch/886794/
which set a fixed pixel rate value to 96MHz, which match perfectly
with the 384MHz value I found for link frequency...

Perhaps other CSI-2 OV5640 users can comment about it and have the 
explanations of what I experiment...
Maxime, Jacopo, do you have any idea about it ?


>> version 2:
>>    - do not set control read only as per Hans' comment:
>>      See https://www.mail-archive.com/linux-media@vger.kernel.org/msg147910.html
>>
>>   drivers/media/i2c/ov5640.c | 10 ++++++++++
>>   1 file changed, 10 insertions(+)
>>
>> diff --git a/drivers/media/i2c/ov5640.c b/drivers/media/i2c/ov5640.c
>> index 82d4ce9..e6307f3 100644
>> --- a/drivers/media/i2c/ov5640.c
>> +++ b/drivers/media/i2c/ov5640.c
>> @@ -218,6 +218,7 @@ struct ov5640_ctrls {
>>   	struct v4l2_ctrl *test_pattern;
>>   	struct v4l2_ctrl *hflip;
>>   	struct v4l2_ctrl *vflip;
>> +	struct v4l2_ctrl *link_freq;
>>   };
>>   
>>   struct ov5640_dev {
>> @@ -2198,6 +2199,10 @@ static int ov5640_try_fmt_internal(struct v4l2_subdev *sd,
>>   	return 0;
>>   }
>>   
>> +static const s64 link_freq_menu_items[] = {
>> +	384000000,
>> +};
>> +
>>   static int ov5640_set_fmt(struct v4l2_subdev *sd,
>>   			  struct v4l2_subdev_pad_config *cfg,
>>   			  struct v4l2_subdev_format *format)
>> @@ -2636,6 +2641,8 @@ static int ov5640_s_ctrl(struct v4l2_ctrl *ctrl)
>>   	case V4L2_CID_VFLIP:
>>   		ret = ov5640_set_ctrl_vflip(sensor, ctrl->val);
>>   		break;
>> +	case V4L2_CID_LINK_FREQ:
>> +		return 0;
>>   	default:
>>   		ret = -EINVAL;
>>   		break;
>> @@ -2703,6 +2710,9 @@ static int ov5640_init_controls(struct ov5640_dev *sensor)
>>   				       V4L2_CID_POWER_LINE_FREQUENCY_AUTO, 0,
>>   				       V4L2_CID_POWER_LINE_FREQUENCY_50HZ);
>>   
>> +	ctrls->link_freq = v4l2_ctrl_new_int_menu(hdl, ops, V4L2_CID_LINK_FREQ,
>> +						  0, 0, link_freq_menu_items);
>> +
>>   	if (hdl->error) {
>>   		ret = hdl->error;
>>   		goto free_ctrls;
>> -- 
>> 2.7.4
>>
> 

BR,
Hugues.