Re: [RFC/PATCH 3/6] V4L: Add g_embedded_data subdev callback

[Sakari Ailus <sakari.ailus@iki.fi>]

Hi Laurent,

Laurent Pinchart wrote:
> On Saturday 18 February 2012 00:33:23 Sylwester Nawrocki wrote:
>> On 02/18/2012 12:23 AM, Laurent Pinchart wrote:
>>>>   struct v4l2_subdev_video_ops {
>>>>   
>>>>   	int (*s_routing)(struct v4l2_subdev *sd, u32 input, u32 output, u32
>>>>
>>>> config); @@ -321,6 +329,8 @@ struct v4l2_subdev_video_ops {
>>>>
>>>>   			     struct v4l2_mbus_config *cfg);
>>>>   	
>>>>   	int (*s_mbus_config)(struct v4l2_subdev *sd,
>>>>   	
>>>>   			     const struct v4l2_mbus_config *cfg);
>>>>
>>>> +	int (*g_embedded_data)(struct v4l2_subdev *sd, unsigned int *size,
>>>> +			       void **buf);
>>>>
>>>>   };
>>>
>>> How is the embedded data transferred from the sensor to the host in your
>>> case ? Over I2C ?
>>
>> It's transferred over MIPI-CSI2 bus and is intercepted by the MIPI-CSI2
>> receiver, before the image data DMA. The MIPI-CSI2 doesn't have its own
>> DMA engine. More details can be found in patch 6/6.
> 
> As the data is transmitted by the device without any polling from the host, 
> shouldn't it just go to a metadata plane in the V4L2 buffer ?

I'd say that if it can be given to the user space separately, a way
should be provided to do that. It's all about timing: software
controlled digital camera depend on that.

Some receivers are also able to put such metadata into a separate memory
area using DMA, such as the OMAP 3 ISP CCP-2 receiver.

Cheers,

-- 
Sakari Ailus
sakari.ailus@iki.fi