Introduction ============ Modern hardwares have various color processing capabilities both at pre-blending and post-blending phases in the color pipeline. The current drm implementation exposes only the post-blending color hardware blocks. Support for pre-blending hardware is missing. There are multiple use cases where pre-blending color hardware will be useful: a) Linearization of input buffers encoded in various transfer functions. b) Color Space conversion c) Tone mapping d) Frame buffer format conversion e) Non-linearization of buffer(apply transfer function) f) 3D Luts and other miscellaneous color operations. Hence, there is a need to expose the color capabilities of the hardware to user-space. This will help userspace/middleware to use display hardware for color processing and blending instead of doing it through GPU shaders. Work done so far and relevant references ======================================== Some implementation is done by Intel and AMD/Igalia to address the same. Broad consensus is there that we need a generic API at drm core to suffice the use case of various HW vendors. Below are the links capturing the discussion so far. Intel's Plane Color Implementation: https://patchwork.freedesktop.org/series/90825/ AMD's Plane Color Implementation: https://patchwork.freedesktop.org/series/116862/ Hackfest conclusions ==================== HDR/Color Hackfest was organised by Redhat to bring all the industry stakeholders together and converge on a common uapi expectations. Participants from Intel, AMD, Nvidia, Collabora, Redhat, Igalia and other prominent user-space developers and maintainers. Discussions happened on the uapi expectations, opens, nature of hardware of multiple hardware vendors, challenges in generalizing the same and the path forward. Consensus was made that drm core should implement descriptive APIs and not go with prescriptive APIs. DRM core should just expose the hardware capabilities; enabling, customizing and programming the same should be done by the user-space. Driver should just honor the user space request without doing any operations internally. Thanks to Simon Ser, for nicely documenting the design consensus and an UAPI RFC which can be referred to here: https://lore.kernel.org/dri-devel/QMers3awXvNCQlyhWdTtsPwkp5ie9bze_hD5nAccFW7a_RXlWjYB7MoUW_8CKLT2bSQwIXVi5H6VULYIxCdgvryZoAoJnC5lZgyK1QWn488=@emersion.fr/ Design considerations ===================== Following are the important aspects taken into account while designing the current RFC proposal: 1. Individual HW blocks can be muxed. (e.g. out of two HW blocks only one can be used) 2. Position of the HW block in the pipeline can be programmable 3. LUTs can be one dimentional or three dimentional 4. Number of LUT entries can vary across platforms 5. Precision of LUT entries can vary across platforms 6. Distribution of LUT entries may vary. e.g Mutli-segmented, Logarithmic, Piece-Wise Linear(PWL) etc 7. There can be parameterized/non-parameterized fixed function HW blocks. e.g. Just a hardware bit, to convert from one color space to another. 8. Custom non-standard HW implementation. 9. Leaving scope for some vendor defined pescriptive implementation if required. 10.Scope to handle any modification in hardware as technology evolves The current proposal takes into account the above considerations while keeping the implementation as generic as possible leaving scope for future additions or modifications. This proposal is also in line to the details mentioned by Simon's RFC covering all the aspects discussed in hackfest. Outline of the implementation ============================ Each Color Hardware block will be represented by a data structure drm_color_op. These color operations will form the building blocks of a color pipeline which best represents the underlying Hardware. Color operations can be re-arranged, substracted or added to create distinct color pipelines to accurately describe the Hardware blocks present in the display engine. In this proposal, a color pipeline is represented as an array of struct drm_color_op. For individual color operation, we add blobs to advertise the capability of the particular Hardware block. This color pipeline is then packaged within a blob for the user space to retrieve it. To advertise the available color pipelines, an immutable ENUM property "GET_COLOR_PIPELINE" is introduced. This enum property has blob id's as values. With each blob id representing a distinct color pipeline based on underlying HW capabilities and their respective combinations. Once the user space decides on a color pipeline, it can set the pipeline and the corresponding data for the hardware blocks within the pipeline with the BLOB property "SET_COLOR_PIPELINE". Refer to Documentation/gpu/rfc/plane_color_pipeline.rst added in the patch IGT and test details ==================== A set of IGT tests is written to demonstrate the usage of the proposed UAPIs along with some sanity validation. Details of the IGT test can be found here: https://patchwork.freedesktop.org/series/123018/ Opens ===== a. To come up with a list of common HW blocks which can be defined generically by the DRM core in agreement with all the stakeholders b. To enhance/finalize the data structure to define segmented LUTs generically. Out of Scope ============ a. The coefficients for CTM and LUT value calculations are out of scope of the proposal. b. The onus of programming the HW blocks and their values is on user-space. Driver will just provide the interface for the same. c. In order to compute LUT values and coefficients, a helper library can be created in user-space. However, it is out of scope for the current proposal. Acknowledgements and credits ============================ There are multiple contributors who have helped us to reach to this proposal. Special mention to Ville Syrjala<ville.syrjala@xxxxxxxxxxxxxxx>, Pekka Paalanen<pekka.paalanen@xxxxxxxxxxxxx>, Simon Ser<contact@xxxxxxxxxxx>, Harry Wentland<harry.wentland@xxxxxxx>, Melissa Wen<mwen@xxxxxxxxxx>, Jonas<jadahl@xxxxxxxxxx>, Sebastian Wick<sebastian.wick@xxxxxxxxxx>, Bhanu<bhanuprakash.modem@xxxxxxxxx> and Shashank<shashank.sharma@xxxxxxx>. Also, thanks to Carlos <csoriano@xxxxxxxxxx> and the Redhat team for organizing the HDR hackfest. UAPI dependency and Usermode development ======================================== The current KMS implementation requires a user space consumer for it to be accepted upstream. Work is ongoing in weston and mutter community to get color management and HDR support implemented in the respective stacks. ================================================================================= We have tried to take care of all the scenarios and use-cases which possibly could exists in the current proposal. Thanks to everyone who has contributed in all color management discussions so far. Let's work together to improve the current proposal and get this thing implemented in upstream linux. All the feedback and suggestions to enhance the design are welcome. Regards, Uma Shankar Chaitanya Kumar Borah Cc: Ville Syrjala <ville.syrjala@xxxxxxxxxxxxxxx> Cc: Pekka Paalanen <pekka.paalanen@xxxxxxxxxxxxx> Cc: Simon Ser <contact@xxxxxxxxxxx> Cc: Harry Wentland <harry.wentland@xxxxxxx> Cc: Melissa Wen <mwen@xxxxxxxxxx> Cc: Jonas Ådahl <jadahl@xxxxxxxxxx> Cc: Sebastian Wick <sebastian.wick@xxxxxxxxxx> Cc: Shashank Sharma <shashank.sharma@xxxxxxx> Cc: Alexander Goins <agoins@xxxxxxxxxx> Chaitanya Kumar Borah (14): drm: Add color operation structure drm: Add plane get color pipeline property drm: Add helper to add color pipeline drm: Manage color blob states drm: Replace individual color blobs drm: Reset pipeline when user sends NULL blob drm: Reset plane color state on pipeline switch request drm/i915/color: Add HDR plane LUT range data to color pipeline drm/i915/color: Add SDR plane LUT range data to color pipeline drm/i915/color: Add color pipelines to plane drm/i915/color: Create and attach set color pipeline property drm/i915/color: Enable plane color features drm/i915/color: Add a dummy pipeline with 3D LUT drm/i915/color: Add example implementation for vendor specific color operation Uma Shankar (19): drm/doc/rfc: Add RFC document for proposed Plane Color Pipeline drm: Add structures for setting color pipeline drm: Add set colorpipeline property drm: Add Enhanced Gamma LUT precision structure drm: Add color lut range structure drm: Add color information to plane state drm/i915/color: Add lut range for SDR planes drm/i915/color: Add lut range for HDR planes drm/i915/color: Add color pipeline for HDR planes drm/i915/color: Add color pipeline for SDR planes drm/i915/color: Add plane color callbacks drm/i915/color: Load plane color luts from atomic flip drm/i915/xelpd: Add plane color check to glk_plane_color_ctl drm/i915/xelpd: Add register definitions for Plane Degamma drm/i915/color: Add color functions for ADL drm/i915/color: Program Plane Pre-CSC Registers drm/i915/xelpd: Add register definitions for Plane Post CSC drm/i915/xelpd: Program Plane Post CSC Registers drm/i915/color: Enable Plane CSC .../gpu/rfc/plane_color_pipeline.rst | 394 ++++++++++ drivers/gpu/drm/drm_atomic_state_helper.c | 21 + drivers/gpu/drm/drm_atomic_uapi.c | 218 ++++++ drivers/gpu/drm/drm_color_mgmt.c | 130 ++++ drivers/gpu/drm/i915/display/intel_color.c | 684 +++++++++++++++++- drivers/gpu/drm/i915/display/intel_color.h | 7 +- .../drm/i915/display/skl_universal_plane.c | 21 +- drivers/gpu/drm/i915/i915_reg.h | 124 ++++ include/drm/drm_plane.h | 82 +++ include/uapi/drm/drm_mode.h | 196 +++++ include/uapi/drm/i915_drm.h | 25 + 11 files changed, 1899 insertions(+), 3 deletions(-) create mode 100644 Documentation/gpu/rfc/plane_color_pipeline.rst -- 2.38.1
