Brief documentation about pre-defined transfer function usage on AMD display driver and standardized EOTFs and inverse EOTFs. Co-developed-by: Harry Wentland <harry.wentland@xxxxxxx> Signed-off-by: Harry Wentland <harry.wentland@xxxxxxx> Signed-off-by: Melissa Wen <mwen@xxxxxxxxxx> --- .../amd/display/amdgpu_dm/amdgpu_dm_color.c | 39 +++++++++++++++++++ 1 file changed, 39 insertions(+) diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c index cc2187c0879a..7f13bcdaf016 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c @@ -85,6 +85,45 @@ void amdgpu_dm_init_color_mod(void) } #ifdef AMD_PRIVATE_COLOR +/* Pre-defined Transfer Functions (TF) + * + * AMD driver supports pre-defined mathematical functions for transferring + * between encoded values and optical/linear space. Depending on HW color caps, + * ROMs and curves built by the AMD color module support these transforms. + * + * The driver-specific color implementation exposes properties for pre-blending + * degamma TF, shaper TF (before 3D LUT), and blend(dpp.ogam) TF and + * post-blending regamma (mpc.ogam) TF. However, only pre-blending degamma + * supports ROM curves. AMD color module uses pre-defined coefficients to build + * curves for the other blocks. What can be done by each color block is + * described by struct dpp_color_capsand struct mpc_color_caps. + * + * AMD driver-specific color API exposes the following pre-defined transfer + * functions: + * + * - Linear/Unity: linear/identity relationship between pixel value and + * luminance value; + * - Gamma 2.2, Gamma 2.4, Gamma 2.6: pure gamma functions; + * - sRGB: 2.4 gamma with small initial linear section as standardized by IEC + * 61966-2-1:1999; + * - BT.709 (BT.1886): 2.4 gamma with differences in the dark end of the scale. + * Used in HD-TV and standardized by ITU-R BT.1886; + * - PQ (Perceptual Quantizer): used for HDR display, allows luminance range + * capability of 0 to 10,000 nits; standardized by SMPTE ST 2084. + * + * In the driver-specific API, color block names attached to TF properties + * suggest the intention regarding non-linear encoding pixel's luminance + * values. As some newer encodings don't use gamma curve, we make encoding and + * decoding explicit by defining an enum list of transfer functions supported + * in terms of EOTF and inverse EOTF, where: + * + * - EOTF (electro-optical transfer function): is the transfer function to go + * from the encoded value to an optical (linear) value. De-gamma functions + * traditionally do this. + * - Inverse EOTF (simply the inverse of the EOTF): is usually intended to go + * from an optical/linear space (which might have been used for blending) + * back to the encoded values. Gamma functions traditionally do this. + */ static const char * const amdgpu_transfer_function_names[] = { [AMDGPU_TRANSFER_FUNCTION_DEFAULT] = "Default", -- 2.40.1