Re: [PATCH v3] drm/exynos: mixer: document YCbCr magic numbers

[Tobias Jakobi <tjakobi@math.uni-bielefeld.de>]

Inki Dae wrote:
> 2017-03-29 20:56 GMT+09:00 Tobias Jakobi <tjakobi@math.uni-bielefeld.de>:
>> Hello Daniel,
>>
>> same question here. Patch doesn't introduce any functional changes (just
>> adds code documentation), so can you merge it through drm-misc?
>>
> 
> Sorry for late. Confirmed just now. I will check it on next Monday.
You have added the wrong patch (v2 instead of v3).

- Tobias


> Thanks,
> Inki Dae
> 
>> With best wishes,
>> Tobias
>>
>>
>> Tobias Jakobi wrote:
>>> The output stage of the mixer uses YCbCr for the internal
>>> computations, which is the reason that some registers take
>>> YCbCr related data as input. In particular this applies
>>> to MXR_BG_COLOR{0,1,2} and MXR_CM_COEFF_{Y,CB,CR}.
>>>
>>> Document the formatting of the data which we write to
>>> these registers.
>>>
>>> While at it, unify wording of comments in the register header.
>>>
>>> Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
>>> Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
>>> ---
>>> Changes in v2:
>>> - use floating point values as input for the macros, as
>>>   suggested by Andrzej
>>> - the floating point values have been tuned to exactly match
>>>   the values that are currently used
>>>
>>> Changes in v3:
>>> - use only three digit values (pointed out by Andrzej)
>>>
>>>  drivers/gpu/drm/exynos/exynos_mixer.c | 33 +++++++++++++++++++++++++--------
>>>  drivers/gpu/drm/exynos/regs-mixer.h   |  7 +++++--
>>>  2 files changed, 30 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/exynos/exynos_mixer.c b/drivers/gpu/drm/exynos/exynos_mixer.c
>>> index 41d0c36..9648dd5 100644
>>> --- a/drivers/gpu/drm/exynos/exynos_mixer.c
>>> +++ b/drivers/gpu/drm/exynos/exynos_mixer.c
>>> @@ -45,6 +45,22 @@
>>>  #define MIXER_WIN_NR         3
>>>  #define VP_DEFAULT_WIN               2
>>>
>>> +/*
>>> + * Mixer color space conversion coefficient triplet.
>>> + * Used for CSC from RGB to YCbCr.
>>> + * Each coefficient is a 10-bit fixed point number with
>>> + * sign and no integer part, i.e.
>>> + * [0:8] = fractional part (representing a value y = x / 2^9)
>>> + * [9] = sign
>>> + * Negative values are encoded with two's complement.
>>> + */
>>> +#define MXR_CSC_C(x) ((int)((x) * 512.0) & 0x3ff)
>>> +#define MXR_CSC_CT(a0, a1, a2) \
>>> +  ((MXR_CSC_C(a0) << 20) | (MXR_CSC_C(a1) << 10) | (MXR_CSC_C(a2) << 0))
>>> +
>>> +/* YCbCr value, used for mixer background color configuration. */
>>> +#define MXR_YCBCR_VAL(y, cb, cr) (((y) << 16) | ((cb) << 8) | ((cr) << 0))
>>> +
>>>  /* The pixelformats that are natively supported by the mixer. */
>>>  #define MXR_FORMAT_RGB565    4
>>>  #define MXR_FORMAT_ARGB1555  5
>>> @@ -391,13 +407,14 @@ static void mixer_cfg_rgb_fmt(struct mixer_context *ctx, unsigned int height)
>>>       case 1080:
>>>       default:
>>>               val = MXR_CFG_RGB709_16_235;
>>> +             /* Configure the BT.709 CSC matrix for full range RGB. */
>>>               mixer_reg_write(res, MXR_CM_COEFF_Y,
>>> -                             (1 << 30) | (94 << 20) | (314 << 10) |
>>> -                             (32 << 0));
>>> +                     MXR_CSC_CT( 0.184,  0.614,  0.063) |
>>> +                     MXR_CM_COEFF_RGB_FULL);
>>>               mixer_reg_write(res, MXR_CM_COEFF_CB,
>>> -                             (972 << 20) | (851 << 10) | (225 << 0));
>>> +                     MXR_CSC_CT(-0.102, -0.338,  0.440));
>>>               mixer_reg_write(res, MXR_CM_COEFF_CR,
>>> -                             (225 << 20) | (820 << 10) | (1004 << 0));
>>> +                     MXR_CSC_CT( 0.440, -0.399, -0.040));
>>>               break;
>>>       }
>>>
>>> @@ -715,10 +732,10 @@ static void mixer_win_reset(struct mixer_context *ctx)
>>>       /* reset default layer priority */
>>>       mixer_reg_write(res, MXR_LAYER_CFG, 0);
>>>
>>> -     /* setting background color */
>>> -     mixer_reg_write(res, MXR_BG_COLOR0, 0x008080);
>>> -     mixer_reg_write(res, MXR_BG_COLOR1, 0x008080);
>>> -     mixer_reg_write(res, MXR_BG_COLOR2, 0x008080);
>>> +     /* set all background colors to RGB (0,0,0) */
>>> +     mixer_reg_write(res, MXR_BG_COLOR0, MXR_YCBCR_VAL(0, 128, 128));
>>> +     mixer_reg_write(res, MXR_BG_COLOR1, MXR_YCBCR_VAL(0, 128, 128));
>>> +     mixer_reg_write(res, MXR_BG_COLOR2, MXR_YCBCR_VAL(0, 128, 128));
>>>
>>>       if (test_bit(MXR_BIT_VP_ENABLED, &ctx->flags)) {
>>>               /* configuration of Video Processor Registers */
>>> diff --git a/drivers/gpu/drm/exynos/regs-mixer.h b/drivers/gpu/drm/exynos/regs-mixer.h
>>> index 7f22df5..c311f57 100644
>>> --- a/drivers/gpu/drm/exynos/regs-mixer.h
>>> +++ b/drivers/gpu/drm/exynos/regs-mixer.h
>>> @@ -140,11 +140,11 @@
>>>  #define MXR_INT_EN_VSYNC             (1 << 11)
>>>  #define MXR_INT_EN_ALL                       (0x0f << 8)
>>>
>>> -/* bit for MXR_INT_STATUS */
>>> +/* bits for MXR_INT_STATUS */
>>>  #define MXR_INT_CLEAR_VSYNC          (1 << 11)
>>>  #define MXR_INT_STATUS_VSYNC         (1 << 0)
>>>
>>> -/* bit for MXR_LAYER_CFG */
>>> +/* bits for MXR_LAYER_CFG */
>>>  #define MXR_LAYER_CFG_GRP1_VAL(x)    MXR_MASK_VAL(x, 11, 8)
>>>  #define MXR_LAYER_CFG_GRP1_MASK              MXR_LAYER_CFG_GRP1_VAL(~0)
>>>  #define MXR_LAYER_CFG_GRP0_VAL(x)    MXR_MASK_VAL(x, 7, 4)
>>> @@ -152,5 +152,8 @@
>>>  #define MXR_LAYER_CFG_VP_VAL(x)              MXR_MASK_VAL(x, 3, 0)
>>>  #define MXR_LAYER_CFG_VP_MASK                MXR_LAYER_CFG_VP_VAL(~0)
>>>
>>> +/* bits for MXR_CM_COEFF_Y */
>>> +#define MXR_CM_COEFF_RGB_FULL                (1 << 30)
>>> +
>>>  #endif /* SAMSUNG_REGS_MIXER_H */
>>>
>>>
>>
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