Re: [PATCH v3 4/5] media: vsp1: Split out pre-filter multiplier

[Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>]

Hi Laurent

On 18/04/2019 07:37, Laurent Pinchart wrote:
> Hi Kieran,
> 
> Thank you for the patch.
> 
> On Thu, Apr 11, 2019 at 05:12:55PM +0100, Kieran Bingham wrote:
>> The 'mp' value is used through many calculations in determining the scaling
>> factors of the UDS. Factor this out so that it can be reused in further
>> calculations, and also ensure that if the BLADV control is ever changed only a
>> single function needs to be modified.
>>
>> Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
>> ---
>>  drivers/media/platform/vsp1/vsp1_uds.c | 22 ++++++++++++++--------
>>  1 file changed, 14 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/media/platform/vsp1/vsp1_uds.c b/drivers/media/platform/vsp1/vsp1_uds.c
>> index 27012af973b2..c71c24363d54 100644
>> --- a/drivers/media/platform/vsp1/vsp1_uds.c
>> +++ b/drivers/media/platform/vsp1/vsp1_uds.c
>> @@ -46,6 +46,18 @@ void vsp1_uds_set_alpha(struct vsp1_entity *entity, struct vsp1_dl_body *dlb,
>>  		       alpha << VI6_UDS_ALPVAL_VAL0_SHIFT);
>>  }
>>  
>> +/*
>> + * Determine the pre-filter multiplication value.
> 
> This would benefit from a more detailed description, and in particular a
> definition of what "pre-filter" means.

There is a pre-filter processing stage to the scaling filter. I think it
does some form of pixel binning. The specifics are not documented.

I could update this to:

/*
 * Determine the pre-filter binning divider
 *
 * The UDS uses a two stage filter scaler process. This determines the
 * rate at which pixels are reduced for large down-scaling ratios before
 * being fed into the bicubic filter.
 */

>> + *
>> + * This calculation assumes that the BLADV control is unset.
> 
> s/control/bit/ ?
> s/unset/not set/ ?
> 

Sure.

>> + */
>> +static unsigned int uds_multiplier(int ratio)
> 
> Should the function be renamed to uds_pre_multiplier() ? And isn't it a
> divisor ? :-)

Indeed in the pipeline, the component is used when  downscaling, and so
I believe it is part of a pre-filter divider.

How about: uds_binning_ratio() ?




>> +{
>> +	unsigned int mp = ratio / 4096;
>> +
>> +	return mp < 4 ? 1 : (mp < 8 ? 2 : 4);
>> +}
>> +
>>  /*
>>   * uds_output_size - Return the output size for an input size and scaling ratio
>>   * @input: input size in pixels
>> @@ -55,10 +67,7 @@ static unsigned int uds_output_size(unsigned int input, unsigned int ratio)
>>  {
>>  	if (ratio > 4096) {
>>  		/* Down-scaling */
>> -		unsigned int mp;
>> -
>> -		mp = ratio / 4096;
>> -		mp = mp < 4 ? 1 : (mp < 8 ? 2 : 4);
>> +		unsigned int mp = uds_multiplier(ratio);
>>  
>>  		return (input - 1) / mp * mp * 4096 / ratio + 1;
>>  	} else {
>> @@ -88,10 +97,7 @@ static unsigned int uds_passband_width(unsigned int ratio)
>>  {
>>  	if (ratio >= 4096) {
>>  		/* Down-scaling */
>> -		unsigned int mp;
>> -
>> -		mp = ratio / 4096;
>> -		mp = mp < 4 ? 1 : (mp < 8 ? 2 : 4);
>> +		unsigned int mp = uds_multiplier(ratio);
>>  
>>  		return 64 * 4096 * mp / ratio;
>>  	} else {
> 
--
Regards

Kieran