Re: [PATCH 24/24] drm/omap: cleanup color space conversion

[Tomi Valkeinen <tomi.valkeinen@ti.com>]

On 27/02/18 16:08, Laurent Pinchart wrote:
> Hi Tomi,
> 
> Thank you for the patch.
> 
> On Monday, 12 February 2018 11:44:54 EET Tomi Valkeinen wrote:
>> The setup code for color space conversion is a bit messy. This patch
>> cleans it up.
>>
>> For some reason the TRM uses values in YCrCb order, which is also used
>> in the current driver, whereas everywhere else it's YCbCr (which also
>> matches YUV order). This patch changes the tables to use the common
>> order to avoid confusion.
>>
>> The tables are split into separate lines, and comments added for
>> clarity.
>>
>> WB color conversion registers are similar but different than non-WB, but
>> the same function was used to write both. It worked fine because the
>> coef table was adjusted accordingly, but that was rather confusing. This
>> patch adds a separate function to write the WB values so that the coef
>> table can be written in an understandable way.
>>
>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
>> ---
>>  drivers/gpu/drm/omapdrm/dss/dispc.c | 59 ++++++++++++++++++++++++++--------
>>  1 file changed, 44 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/omapdrm/dss/dispc.c
>> b/drivers/gpu/drm/omapdrm/dss/dispc.c index ff09e2be470f..697274317f7c
>> 100644
>> --- a/drivers/gpu/drm/omapdrm/dss/dispc.c
>> +++ b/drivers/gpu/drm/omapdrm/dss/dispc.c
>> @@ -345,11 +345,6 @@ static const struct {
>>  	},
>>  };
>>
>> -struct color_conv_coef {
>> -	int ry, rcr, rcb, gy, gcr, gcb, by, bcr, bcb;
>> -	int full_range;
>> -};
>> -
>>  static unsigned long dispc_fclk_rate(void);
>>  static unsigned long dispc_core_clk_rate(void);
>>  static unsigned long dispc_mgr_lclk_rate(enum omap_channel channel);
>> @@ -841,9 +836,18 @@ static void dispc_ovl_set_scale_coef(enum omap_plane_id
>> plane, int fir_hinc, }
>>  }
>>
>> +struct csc_coef_yuv2rgb {
>> +	int ry, rcb, rcr, gy, gcb, gcr, by, bcb, bcr;
> 
> If you made this a 3x3 matrix without explicit names for the fields I think 
> you wouldn't need two structure and two functions.

That is true, but I think it would also make the code more difficult to
follow. It's not exactly obvious which coefficients go where.

>> +	bool full_range;
>> +};
>> +
>> +struct csc_coef_rgb2yuv {
>> +	int yr, yg, yb, cbr, cbg, cbb, crr, crg, crb;
>> +	bool full_range;
>> +};
>>
>>  static void dispc_ovl_write_color_conv_coef(enum omap_plane_id plane,
>> -		const struct color_conv_coef *ct)
>> +		const struct csc_coef_yuv2rgb *ct)
>>  {
>>  #define CVAL(x, y) (FLD_VAL(x, 26, 16) | FLD_VAL(y, 10, 0))
>>
>> @@ -853,7 +857,24 @@ static void dispc_ovl_write_color_conv_coef(enum
>> omap_plane_id plane, dispc_write_reg(DISPC_OVL_CONV_COEF(plane, 3),
>> CVAL(ct->bcr, ct->by)); dispc_write_reg(DISPC_OVL_CONV_COEF(plane, 4),
>> CVAL(0, ct->bcb));
>>
>> -	REG_FLD_MOD(DISPC_OVL_ATTRIBUTES(plane), ct->full_range, 11, 11);
>> +	REG_FLD_MOD(DISPC_OVL_ATTRIBUTES(plane), !!ct->full_range, 11, 11);
> 
> true and false should be equal to 1 and 0 respectively, so the !! shouldn't be 
> needed.

Yep.

>> +
>> +#undef CVAL
>> +}
>> +
>> +static void dispc_wb_write_color_conv_coef(const struct csc_coef_rgb2yuv
>> *ct)
>> +{
>> +	const enum omap_plane_id plane = OMAP_DSS_WB;
>> +
>> +#define CVAL(x, y) (FLD_VAL(x, 26, 16) | FLD_VAL(y, 10, 0))
>> +
>> +	dispc_write_reg(DISPC_OVL_CONV_COEF(plane, 0), CVAL(ct->yg,  ct->yr));
>> +	dispc_write_reg(DISPC_OVL_CONV_COEF(plane, 1), CVAL(ct->crr, ct->yb));
>> +	dispc_write_reg(DISPC_OVL_CONV_COEF(plane, 2), CVAL(ct->crb, ct->crg));
>> +	dispc_write_reg(DISPC_OVL_CONV_COEF(plane, 3), CVAL(ct->cbg, ct->cbr));
>> +	dispc_write_reg(DISPC_OVL_CONV_COEF(plane, 4), CVAL(0, ct->cbb));
>> +
>> +	REG_FLD_MOD(DISPC_OVL_ATTRIBUTES(plane), !!ct->full_range, 11, 11);
>>
>>  #undef CVAL
>>  }
>> @@ -862,20 +883,28 @@ static void dispc_setup_color_conv_coef(void)
>>  {
>>  	int i;
>>  	int num_ovl = dispc_get_num_ovls();
>> -	const struct color_conv_coef ctbl_bt601_5_ovl = {
>> -		/* YUV -> RGB */
>> -		298, 409, 0, 298, -208, -100, 298, 0, 517, 0,
>> +
>> +	/* YUV -> RGB, ITU-R BT.601, limited range */
>> +	const struct csc_coef_yuv2rgb coefs_yuv2rgb_bt601_lim = {
>> +		298,    0,  409,	/* ry, rcb, rcr */
>> +		298, -100, -208,	/* gy, gcb, gcr */
>> +		298,  516,    0,	/* by, bcb, bcr */
> 
> The 517 turned into 516, was that intentional ?

Good point. It's been a while, but I did recalculate these, and with
rounding, all the other values match except the 517, so I changed it
according to my calculations.

That said, I'm not sure if the original calculations are correct, as
they seem to use 256 as multiplier, which would not result 0xff from 1.0
value. In any case, I changed the single value that seemed to be off
from the other ones.

 Tomi

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