Re: [PATCH v4 01/11] drm/colorop: Add DRM_COLOROP_FIXED_MATRIX

On 2026-07-30 06:59, Pekka Paalanen wrote:
> On Wed, 22 Jul 2026 09:45:57 -0400
> Harry Wentland <[email protected]> wrote:
> 
>> From: Chaitanya Kumar Borah <[email protected]>
>>
>> Introduce DRM_COLOROP_FIXED_MATRIX, a new colorop type representing a
>> hardware that performs a fixed matrix operation.
>>
>> Unlike CTM-based colorops, this block does not expose programmable
>> coefficients. Instead, userspace selects one of the predefined
>> hardware modes via a new FIXED_MATRIX_TYPE enum property. Supported modes
>> include common YCbCr->RGB and RGB709->RGB2020 conversions.
>>
>> v4:
>>  - Add limited-range YCbCr-RGB conversion matrix enums (Robert)
>>  - Document matrix values (Pekka)
>>  - Clarify RGB709 to RGB2020 is a full-range matrix (Pekka)
>>  - Fix confusing "CSC preset" doc (Pekka)
>>
>> v2:
>>  - Naming changes (Pekka)
>>
>> v3:
>>  - Fix NC matrix enum name and string (Melissa)
>>  - Rebase
>>
>> Co-developed-by: Harry Wentland <[email protected]>
>> Signed-off-by: Chaitanya Kumar Borah <[email protected]>
>> Signed-off-by: Harry Wentland <[email protected]>
>> Reviewed-by: Melissa Wen <[email protected]>
>> Reviewed-by: Harry Wentland <[email protected]>
>> Reviewed-by: Robert Mader <[email protected]>
>> ---
>>  drivers/gpu/drm/drm_atomic.c      |   4 +
>>  drivers/gpu/drm/drm_atomic_uapi.c |   7 ++
>>  drivers/gpu/drm/drm_colorop.c     | 109 ++++++++++++++++++++
>>  include/drm/drm_colorop.h         | 159 ++++++++++++++++++++++++++++++
>>  include/uapi/drm/drm_mode.h       |  12 +++
>>  5 files changed, 291 insertions(+)
> 
>> diff --git a/drivers/gpu/drm/drm_colorop.c b/drivers/gpu/drm/drm_colorop.c
>> index 682fcc651525..e7ccf7d053b8 100644
>> --- a/drivers/gpu/drm/drm_colorop.c
>> +++ b/drivers/gpu/drm/drm_colorop.c
>> @@ -68,6 +68,7 @@ static const struct drm_prop_enum_list drm_colorop_type_enum_list[] = {
>>  	{ DRM_COLOROP_CTM_3X4, "3x4 Matrix"},
>>  	{ DRM_COLOROP_MULTIPLIER, "Multiplier"},
>>  	{ DRM_COLOROP_3D_LUT, "3D LUT"},
>> +	{ DRM_COLOROP_FIXED_MATRIX, "Fixed Matrix"},
>>  };
>>  
>>  static const char * const colorop_curve_1d_type_names[] = {
>> @@ -90,6 +91,17 @@ static const struct drm_prop_enum_list drm_colorop_lut3d_interpolation_list[] =
>>  	{ DRM_COLOROP_LUT3D_INTERPOLATION_TETRAHEDRAL, "Tetrahedral" },
>>  };
>>  
>> +static const char * const colorop_fixed_matrix_type_names[] = {
>> +	[DRM_COLOROP_FM_YCBCR601_FULL_RGB] = "YCbCr 601 Full to RGB",
>> +	[DRM_COLOROP_FM_YCBCR601_LIMITED_RGB] = "YCbCr 601 Limited to RGB",
>> +	[DRM_COLOROP_FM_YCBCR709_FULL_RGB] = "YCbCr 709 Full to RGB",
>> +	[DRM_COLOROP_FM_YCBCR709_LIMITED_RGB] = "YCbCr 709 Limited to RGB",
>> +	[DRM_COLOROP_FM_YCBCR2020_NC_FULL_RGB] = "YCbCr 2020 NC Full to RGB",
>> +	[DRM_COLOROP_FM_YCBCR2020_NC_LIMITED_RGB] = "YCbCr 2020 NC Limited to RGB",
>> +	[DRM_COLOROP_FM_YCBCR_LIMITED_FULL] = "YCbCr limited to full",
>> +	[DRM_COLOROP_FM_RGB709_RGB2020] = "RGB709 to RGB2020",
>> +};
> 
> 
>> diff --git a/include/drm/drm_colorop.h b/include/drm/drm_colorop.h
>> index 224fae40ed2b..92eb6463c39f 100644
>> --- a/include/drm/drm_colorop.h
>> +++ b/include/drm/drm_colorop.h
>> @@ -134,6 +134,146 @@ enum drm_colorop_curve_1d_type {
>>  	DRM_COLOROP_1D_CURVE_COUNT
>>  };
>>  
>> +/**
>> + * enum drm_colorop_fixed_matrix_type - type of Fixed Matrix
>> + *
>> + * Describes a Fixed Matrix operation to be applied by the DRM_COLOROP_FIXED_MATRIX
>> + */
>> +enum drm_colorop_fixed_matrix_type {
>> +	/**
>> +	 * @DRM_COLOROP_FM_YCBCR601_FULL_RGB:
>> +	 *
>> +	 * enum string "YCbCr 601 Full to RGB"
>> +	 *
>> +	 * Converts full-range YCbCr into full-range RGB using the BT.601
>> +	 * coefficients. Y is normalized to [0, 1] and Cb, Cr are centered
>> +	 * at 0 (the nominal 0.5 offset removed) before the matrix::
>> +	 *
>> +	 *   | R |   | 1.0   0.000000   1.402000 |   | Y  |
>> +	 *   | G | = | 1.0  -0.344136  -0.714136 | x | Cb |
>> +	 *   | B |   | 1.0   1.772000   0.000000 |   | Cr |
>> +	 */
>> +	DRM_COLOROP_FM_YCBCR601_FULL_RGB,
>> +
>> +	/**
>> +	 * @DRM_COLOROP_FM_YCBCR601_LIMITED_RGB:
>> +	 *
>> +	 * enum string "YCbCr 601 Limited to RGB"
>> +	 *
>> +	 * Converts limited- (narrow-) range YCbCr into full-range RGB using
>> +	 * the BT.601 coefficients. Before the matrix Y is offset by 16/255
>> +	 * and Cb, Cr are centered at 0, following the studio-range
>> +	 * convention of ITU-R BT.601::
>> +	 *
>> +	 *   | R |   | 1.164384   0.000000   1.596027 |   | Y - 16/255 |
>> +	 *   | G | = | 1.164384  -0.391762  -0.812968 | x | Cb         |
>> +	 *   | B |   | 1.164384   2.017232   0.000000 |   | Cr         |
>> +	 */
>> +	DRM_COLOROP_FM_YCBCR601_LIMITED_RGB,
>> +
>> +	/**
>> +	 * @DRM_COLOROP_FM_YCBCR709_FULL_RGB:
>> +	 *
>> +	 * enum string "YCbCr 709 Full to RGB"
>> +	 *
>> +	 * Converts full-range YCbCr into full-range RGB using the BT.709
>> +	 * coefficients. Y is normalized to [0, 1] and Cb, Cr are centered
>> +	 * at 0 (the nominal 0.5 offset removed) before the matrix::
>> +	 *
>> +	 *   | R |   | 1.0   0.000000   1.574800 |   | Y  |
>> +	 *   | G | = | 1.0  -0.187324  -0.468124 | x | Cb |
>> +	 *   | B |   | 1.0   1.855600   0.000000 |   | Cr |
>> +	 */
>> +	DRM_COLOROP_FM_YCBCR709_FULL_RGB,
>> +
>> +	/**
>> +	 * @DRM_COLOROP_FM_YCBCR709_LIMITED_RGB:
>> +	 *
>> +	 * enum string "YCbCr 709 Limited to RGB"
>> +	 *
>> +	 * Converts limited- (narrow-) range YCbCr into full-range RGB using
>> +	 * the BT.709 coefficients. Before the matrix Y is offset by 16/255
>> +	 * and Cb, Cr are centered at 0, following the studio-range
>> +	 * convention of ITU-R BT.709::
>> +	 *
>> +	 *   | R |   | 1.164384   0.000000   1.792741 |   | Y - 16/255 |
>> +	 *   | G | = | 1.164384  -0.213249  -0.532909 | x | Cb         |
>> +	 *   | B |   | 1.164384   2.112402   0.000000 |   | Cr         |
>> +	 */
>> +	DRM_COLOROP_FM_YCBCR709_LIMITED_RGB,
>> +
>> +	/**
>> +	 * @DRM_COLOROP_FM_YCBCR2020_NC_FULL_RGB:
>> +	 *
>> +	 * enum string "YCbCr 2020 NC Full to RGB"
>> +	 *
>> +	 * Converts full-range YCbCr into full-range RGB using the BT.2020
>> +	 * non-constant luminance coefficients. Y is normalized to [0, 1]
>> +	 * and Cb, Cr are centered at 0 (the nominal 0.5 offset removed)
>> +	 * before the matrix::
>> +	 *
>> +	 *   | R |   | 1.0   0.000000   1.474600 |   | Y  |
>> +	 *   | G | = | 1.0  -0.164553  -0.571353 | x | Cb |
>> +	 *   | B |   | 1.0   1.881400   0.000000 |   | Cr |
>> +	 */
>> +	DRM_COLOROP_FM_YCBCR2020_NC_FULL_RGB,
>> +
>> +	/**
>> +	 * @DRM_COLOROP_FM_YCBCR2020_NC_LIMITED_RGB:
>> +	 *
>> +	 * enum string "YCbCr 2020 NC Limited to RGB"
>> +	 *
>> +	 * Converts limited- (narrow-) range YCbCr into full-range RGB using
>> +	 * the BT.2020 non-constant luminance coefficients. Before the matrix
>> +	 * Y is offset by 16/255 and Cb, Cr are centered at 0, following the
>> +	 * studio-range convention of ITU-R BT.2020::
>> +	 *
>> +	 *   | R |   | 1.164384   0.000000   1.678674 |   | Y - 16/255 |
>> +	 *   | G | = | 1.164384  -0.187326  -0.650424 | x | Cb         |
>> +	 *   | B |   | 1.164384   2.141772   0.000000 |   | Cr         |
>> +	 */
>> +	DRM_COLOROP_FM_YCBCR2020_NC_LIMITED_RGB,
>> +
>> +	/**
>> +	 * @DRM_COLOROP_FM_YCBCR_LIMITED_FULL:
>> +	 *
>> +	 * enum string "YCbCr limited to full"
>> +	 *
>> +	 * Converts limited- (narrow-) range YCbCr into full-range YCbCr.
>> +	 * Though not strictly a matrix operation it can be represented as
>> +	 * one. Luma is expanded by 255/219 and chroma by 255/224, keeping
>> +	 * the black level (16/255) and chroma neutral point (0.5) fixed::
>> +	 *
>> +	 *   | Y'      |   | 1.164384  0.000000  0.000000 |   | Y - 16/255 |
>> +	 *   | Cb'-0.5 | = | 0.000000  1.138393  0.000000 | x | Cb - 0.5   |
>> +	 *   | Cr'-0.5 |   | 0.000000  0.000000  1.138393 |   | Cr - 0.5   |
>> +	 */
> 
> Hi Harry,
> 
> the prime notation (Y') is often used to signify an electrical domain
> while in the same context stimulus variables without prime signify an
> optical domain. Using both forms here might cause some confusion.
> Instead of an equals sign, maybe you could use an arrow to avoid having
> to rename all YCbCr variables? (e.g. x ← x + 1)
> 
> About the chroma offset for both ranges on all coefficients; it depends
> on the number of bits per channel B such that
> 
> 	N = 1 << B
> 	offset = (N / 2) / (N - 1)
> 
> I assume the drivers and hardware get this right, but I feel a little
> uncomfortable letting this approximation into the documentation since,
> strictly speaking, it's incorrect.
> 

I'm dropping DRM_COLOROP_FM_YCBCR_LIMITED_FULL and DRM_COLOROP_FM_RGB709_RGB2020
from v5 because we don't have any good non-IGT usermode testing these currently,
to my knowledge.

Chaitanya, I expect you'll re-add them for your Intel series. Make sure to take
Pekka's comments into account then. Would like to see how these fit into any
compositor implementation.

Harry

> 
>> +	DRM_COLOROP_FM_YCBCR_LIMITED_FULL,
>> +
>> +	/**
>> +	 * @DRM_COLOROP_FM_RGB709_RGB2020:
>> +	 *
>> +	 * enum string "RGB709 to RGB2020"
>> +	 *
>> +	 * Selects the matrix that converts full-range RGB with BT.709
>> +	 * primaries to full-range RGB with BT.2020 primaries. The
>> +	 * coefficients match the RGB-to-RGB conversion defined in
>> +	 * ITU-R BT.2087::
>> +	 *
>> +	 *   | R2020 |   | 0.6274  0.3293  0.0433 |   | R709 |
>> +	 *   | G2020 | = | 0.0691  0.9195  0.0114 | x | G709 |
>> +	 *   | B2020 |   | 0.0164  0.0880  0.8956 |   | B709 |
>> +	 */
>> +	DRM_COLOROP_FM_RGB709_RGB2020,
>> +
>> +	/**
>> +	 * @DRM_COLOROP_FM_COUNT:
>> +	 *
>> +	 * enum value denoting the size of the enum
>> +	 */
>> +	DRM_COLOROP_FM_COUNT
>> +};
> 
> I have verified all the matrices listed above.
> 
> I would prefer to see the notational issues addressed, but with or
> without:
> 
> Reviewed-by: Pekka Paalanen <[email protected]>
> 
> 
> Thanks,
> pq