Re: [PATCH RFC] libv4lconvert: SDR conversion from U8 to FLOAT

[Hans Verkuil <hverkuil@xs4all.nl>]

On 11/11/2013 02:40 PM, Antti Palosaari wrote:
> On 11.11.2013 15:14, Hans Verkuil wrote:
>> On 11/10/2013 06:16 PM, Antti Palosaari wrote:
>>> Convert unsigned 8 to float 32 [-1 to +1], which is commonly
>>> used format for baseband signals.
>>>
>>> Signed-off-by: Antti Palosaari <crope@iki.fi>
>>> ---
>>>   contrib/freebsd/include/linux/videodev2.h |  4 ++++
>>>   include/linux/videodev2.h                 |  4 ++++
>>>   lib/libv4lconvert/libv4lconvert.c         | 29 ++++++++++++++++++++++++++++-
>>>   3 files changed, 36 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/contrib/freebsd/include/linux/videodev2.h b/contrib/freebsd/include/linux/videodev2.h
>>> index 1fcfaeb..8829400 100644
>>> --- a/contrib/freebsd/include/linux/videodev2.h
>>> +++ b/contrib/freebsd/include/linux/videodev2.h
>>> @@ -465,6 +465,10 @@ struct v4l2_pix_format {
>>>   #define V4L2_PIX_FMT_SE401      v4l2_fourcc('S', '4', '0', '1') /* se401 janggu compressed rgb */
>>>   #define V4L2_PIX_FMT_S5C_UYVY_JPG v4l2_fourcc('S', '5', 'C', 'I') /* S5C73M3 interleaved UYVY/JPEG */
>>>
>>> +/* SDR */
>>> +#define V4L2_PIX_FMT_FLOAT    v4l2_fourcc('D', 'F', '3', '2') /* float 32-bit */
>>> +#define V4L2_PIX_FMT_U8       v4l2_fourcc('D', 'U', '0', '8') /* unsigned 8-bit */
>>> +
>>>   /*
>>>    *	F O R M A T   E N U M E R A T I O N
>>>    */
>>> diff --git a/include/linux/videodev2.h b/include/linux/videodev2.h
>>> index 437f1b0..14299a6 100644
>>> --- a/include/linux/videodev2.h
>>> +++ b/include/linux/videodev2.h
>>> @@ -431,6 +431,10 @@ struct v4l2_pix_format {
>>>   #define V4L2_PIX_FMT_SE401      v4l2_fourcc('S', '4', '0', '1') /* se401 janggu compressed rgb */
>>>   #define V4L2_PIX_FMT_S5C_UYVY_JPG v4l2_fourcc('S', '5', 'C', 'I') /* S5C73M3 interleaved UYVY/JPEG */
>>>
>>> +/* SDR */
>>> +#define V4L2_PIX_FMT_FLOAT    v4l2_fourcc('D', 'F', '3', '2') /* float 32-bit */
>>> +#define V4L2_PIX_FMT_U8       v4l2_fourcc('D', 'U', '0', '8') /* unsigned 8-bit */
>>
>> I would prefer V4L2_PIX_FMT_SDR_FLOAT and _FMT_SDR_U8.
>>
>> That way it is clear that this format refers to - and should be interpreted as - an SDR format.
>>
>> Otherwise it looks fine to me (but it needs to be documented as well, of course).
> 
> Thanks for the comments!
> 
> What do you think is it OK to abuse/reuse pixelformat for radio signals? 
> Basically the only one field needed is just that, whilst those image 
> only fields (width/height) are not needed at all. Good point to reuse 
> existing things as much as possible is that it does not bloat Kernel 
> data structures etc.

I've no problems with that. While usually the buffers contain images, this
is not always the case. Strictly speaking it is just a DMA API and pixelformat
is used to define the contents. We use it to transport VBI data as well, and
in rare cases even audio (even though we shouldn't).

Regards,

	Hans

> I am also going to make some tests to find out if actual float 
> conversion is faster against pre-calculated LUT, in Kernel or in 
> libv4lconvert and so. Worst scenario I have currently is Mirics ADC with 
> 14-bit resolution => 16384 quantization levels => 32-bit float LUT will 
> be 16384 * 4 = 65536 bytes. Wonder if that much big LUT is allowed to 
> library - but maybe you could alloc() and populate LUT on the fly if 
> needed. Or maybe native conversion is fast enough.
> 
> regards
> Antti
> 
> 
>>
>> Regards,
>>
>> 	Hans
>>
>>> +
>>>   /*
>>>    *	F O R M A T   E N U M E R A T I O N
>>>    */
>>> diff --git a/lib/libv4lconvert/libv4lconvert.c b/lib/libv4lconvert/libv4lconvert.c
>>> index e2afc27..38c9125 100644
>>> --- a/lib/libv4lconvert/libv4lconvert.c
>>> +++ b/lib/libv4lconvert/libv4lconvert.c
>>> @@ -78,7 +78,8 @@ static void v4lconvert_get_framesizes(struct v4lconvert_data *data,
>>>   	{ V4L2_PIX_FMT_RGB24,		24,	 1,	 5,	0 }, \
>>>   	{ V4L2_PIX_FMT_BGR24,		24,	 1,	 5,	0 }, \
>>>   	{ V4L2_PIX_FMT_YUV420,		12,	 6,	 1,	0 }, \
>>> -	{ V4L2_PIX_FMT_YVU420,		12,	 6,	 1,	0 }
>>> +	{ V4L2_PIX_FMT_YVU420,		12,	 6,	 1,	0 }, \
>>> +	{ V4L2_PIX_FMT_FLOAT,		 0,	 0,	 0,	0 }
>>>
>>>   static const struct v4lconvert_pixfmt supported_src_pixfmts[] = {
>>>   	SUPPORTED_DST_PIXFMTS,
>>> @@ -131,6 +132,8 @@ static const struct v4lconvert_pixfmt supported_src_pixfmts[] = {
>>>   	{ V4L2_PIX_FMT_Y6,		 8,	20,	20,	0 },
>>>   	{ V4L2_PIX_FMT_Y10BPACK,	10,	20,	20,	0 },
>>>   	{ V4L2_PIX_FMT_Y16,		16,	20,	20,	0 },
>>> +	/* SDR formats */
>>> +	{ V4L2_PIX_FMT_U8,		0,	0,	0,	0 },
>>>   };
>>>
>>>   static const struct v4lconvert_pixfmt supported_dst_pixfmts[] = {
>>> @@ -1281,6 +1284,25 @@ static int v4lconvert_convert_pixfmt(struct v4lconvert_data *data,
>>>   		}
>>>   		break;
>>>
>>> +	/* SDR */
>>> +	case V4L2_PIX_FMT_U8:
>>> +		switch (dest_pix_fmt) {
>>> +		case V4L2_PIX_FMT_FLOAT:
>>> +			{
>>> +				/* 8-bit unsigned to 32-bit float */
>>> +				unsigned int i;
>>> +				float ftmp;
>>> +				for (i = 0; i < src_size; i++) {
>>> +					ftmp = *src++;
>>> +					ftmp -= 127.5;
>>> +					ftmp /= 127.5;
>>> +					memcpy(dest, &ftmp, 4);
>>> +					dest += 4;
>>> +				}
>>> +			}
>>> +		}
>>> +		break;
>>> +
>>>   	default:
>>>   		V4LCONVERT_ERR("Unknown src format in conversion\n");
>>>   		errno = EINVAL;
>>> @@ -1349,6 +1371,11 @@ int v4lconvert_convert(struct v4lconvert_data *data,
>>>   		temp_needed =
>>>   			my_src_fmt.fmt.pix.width * my_src_fmt.fmt.pix.height * 3 / 2;
>>>   		break;
>>> +	/* SDR */
>>> +	case V4L2_PIX_FMT_FLOAT:
>>> +		dest_needed = src_size * 4; /* 8-bit to 32-bit */
>>> +		temp_needed = dest_needed;
>>> +		break;
>>>   	default:
>>>   		V4LCONVERT_ERR("Unknown dest format in conversion\n");
>>>   		errno = EINVAL;
>>>
>>
> 
>