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author | Melissa Wen <mwen@igalia.com> | 2023-11-16 18:57:47 -0100 |
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committer | Alex Deucher <alexander.deucher@amd.com> | 2023-12-13 15:09:54 -0500 |
commit | e4cddd51bfab2a40529a4af35bd2c912b5a0c239 (patch) | |
tree | 7e5a5d2c0ad9c89c736fc376b5a0d8b612f647eb /drivers/gpu/drm/amd/display | |
parent | 5a3b965b5810bd602d2c7d8ea79ffe8c6e81268d (diff) | |
download | linux-stable-e4cddd51bfab2a40529a4af35bd2c912b5a0c239.tar.gz linux-stable-e4cddd51bfab2a40529a4af35bd2c912b5a0c239.tar.bz2 linux-stable-e4cddd51bfab2a40529a4af35bd2c912b5a0c239.zip |
drm/amd/display: document AMDGPU pre-defined transfer functions
Brief documentation about pre-defined transfer function usage on AMD
display driver and standardized EOTFs and inverse EOTFs.
v3:
- Document BT709 OETF (Pekka)
- Fix description of sRGB and pure power funcs (Pekka)
v4:
- Add description of linear and non-linear forms (Harry)
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Co-developed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Diffstat (limited to 'drivers/gpu/drm/amd/display')
-rw-r--r-- | drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c | 62 |
1 files changed, 62 insertions, 0 deletions
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 a32abbd93a61..49faaf606cfe 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 +85,68 @@ 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: + * + * - Identity: linear/identity relationship between pixel value and + * luminance value; + * - Gamma 2.2, Gamma 2.4, Gamma 2.6: pure power functions; + * - sRGB: 2.4: The piece-wise transfer function from IEC 61966-2-1:1999; + * - BT.709: has a linear segment in the bottom part and then a power function + * with a 0.45 (~1/2.22) gamma for the rest of the range; standardized by + * ITU-R BT.709-6; + * - PQ (Perceptual Quantizer): used for HDR display, allows luminance range + * capability of 0 to 10,000 nits; standardized by SMPTE ST 2084. + * + * The AMD color model is designed with an assumption that SDR (sRGB, BT.709, + * Gamma 2.2, etc.) peak white maps (normalized to 1.0 FP) to 80 nits in the PQ + * system. This has the implication that PQ EOTF (non-linear to linear) maps to + * [0.0..125.0] where 125.0 = 10,000 nits / 80 nits. + * + * Non-linear and linear forms are described in the table below: + * + * ┌───────────┬─────────────────────┬──────────────────────┐ + * │ │ Non-linear │ Linear │ + * ├───────────┼─────────────────────┼──────────────────────┤ + * │ sRGB │ UNORM or [0.0, 1.0] │ [0.0, 1.0] │ + * ├───────────┼─────────────────────┼──────────────────────┤ + * │ BT709 │ UNORM or [0.0, 1.0] │ [0.0, 1.0] │ + * ├───────────┼─────────────────────┼──────────────────────┤ + * │ Gamma 2.x │ UNORM or [0.0, 1.0] │ [0.0, 1.0] │ + * ├───────────┼─────────────────────┼──────────────────────┤ + * │ PQ │ UNORM or FP16 CCCS* │ [0.0, 125.0] │ + * ├───────────┼─────────────────────┼──────────────────────┤ + * │ Identity │ UNORM or FP16 CCCS* │ [0.0, 1.0] or CCCS** │ + * └───────────┴─────────────────────┴──────────────────────┘ + * * CCCS: Windows canonical composition color space + * ** Respectively + * + * 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", |