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Nathan Lucas 3b906e1dc7 drm/amd/display: fix BT.2020 YCbCr limited output CSC matrix
COLOR_SPACE_YCBCR2020_TYPE, which is selected for
COLOR_SPACE_2020_YCBCR_LIMITED color_space, has coefficients that are
incorrect for limited-range output. Its luma and chroma scaling is
full-range so output is too bright and colors are incorrect.

COLOR_SPACE_YCBCR2020_TYPE is closer to a full-range conversion matrix with
incorrect luma offset, so correct the luma offset for full-range and rename
it to COLOR_SPACE_YCBCR2020_FULL_TYPE.

Add COLOR_SPACE_YCBCR2020_LIMITED_TYPE with correct scaling and range for
limited-range output.

Fix related functions so COLOR_SPACE_YCBCR2020_LIMITED_TYPE and
COLOR_SPACE_YCBCR2020_FULL_TYPE are correctly selected based on
dc_color_space.

Derivation of both matrices follows ITU-T H.273:

Table 4, MatrixCoefficients 9, BT.2020-NCL weights:
KR = 0.2627, KB = 0.0593, KG = 1 - KR - KB = 0.6780.

Equations 45-47 in matrix form:
            [  KR             KG             KB            0 ]
M2020_NCL = [ -KR/(2(1-KB))  -KG/(2(1-KB))   1/2           0 ]
            [  1/2           -KG/(2(1-KR))  -KB/(2(1-KR))  0 ]
            [  0              0              0             1 ]

Limited and Full transforms based on equations 30-32 and 36-38 with bit
depth 10, normalized by 1023:

            [ 876/1023   0         0         64/1023  ]
MLimited  = [ 0          896/1023  0         512/1023 ]
            [ 0          0         896/1023  512/1023 ]
            [ 0          0         0         1        ]

            [ 1023/1023  0         0         0        ]
    MFull = [ 0          1023/1023 0         512/1023 ]
            [ 0          0         1023/1023 512/1023 ]
            [ 0          0         0         1        ]

M2020_NCL_Limited = MLimited x M2020_NCL
M2020_NCL_Full    = MFull x M2020_NCL

The upper three rows of M2020_NCL_* are stored in CR, Y, CB order. Each
M2020_NCL_* value is stored as Round(value * 8192) in its 16-bit
two's-complement representation.

Fixes: 973a9c810c ("drm/amd/display: Fix COLOR_SPACE_YCBCR2020_TYPE matrix")
Assisted-by: OpenAI-Codex:GPT-5.6-Sol
Tested-by: Igor Paunovic <royalnet026@gmail.com>
Tested-by: Satyajit Roy <sroy14@alum.utk.edu>
Signed-off-by: Nathan Lucas <nlucasgit@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
History 2026-08-12 09:42:44 -04:00
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Linux kernel
============

The Linux kernel is the core of any Linux operating system. It manages hardware,
system resources, and provides the fundamental services for all other software.

Quick Start
-----------

* Report a bug: See Documentation/admin-guide/reporting-issues.rst
* Get the latest kernel: https://kernel.org
* Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst
* Join the community: https://lore.kernel.org/

Essential Documentation
-----------------------

All users should be familiar with:

* Building requirements: Documentation/process/changes.rst
* Code of Conduct: Documentation/process/code-of-conduct.rst
* License: See COPYING

Documentation can be built with make htmldocs or viewed online at:
https://www.kernel.org/doc/html/latest/


Who Are You?
============

Find your role below:

* New Kernel Developer - Getting started with kernel development
* Academic Researcher - Studying kernel internals and architecture
* Security Expert - Hardening and vulnerability analysis
* Backport/Maintenance Engineer - Maintaining stable kernels
* System Administrator - Configuring and troubleshooting
* Maintainer - Leading subsystems and reviewing patches
* Hardware Vendor - Writing drivers for new hardware
* Distribution Maintainer - Packaging kernels for distros
* AI Coding Assistant - LLMs and AI-powered development tools


For Specific Users
==================

New Kernel Developer
--------------------

Welcome! Start your kernel development journey here:

* Getting Started: Documentation/process/development-process.rst
* Your First Patch: Documentation/process/submitting-patches.rst
* Coding Style: Documentation/process/coding-style.rst
* Build System: Documentation/kbuild/index.rst
* Development Tools: Documentation/dev-tools/index.rst
* Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst
* Core APIs: Documentation/core-api/index.rst

Academic Researcher
-------------------

Explore the kernel's architecture and internals:

* Researcher Guidelines: Documentation/process/researcher-guidelines.rst
* Memory Management: Documentation/mm/index.rst
* Scheduler: Documentation/scheduler/index.rst
* Networking Stack: Documentation/networking/index.rst
* Filesystems: Documentation/filesystems/index.rst
* RCU (Read-Copy Update): Documentation/RCU/index.rst
* Locking Primitives: Documentation/locking/index.rst
* Power Management: Documentation/power/index.rst

Security Expert
---------------

Security documentation and hardening guides:

* Security Documentation: Documentation/security/index.rst
* LSM Development: Documentation/security/lsm-development.rst
* Self Protection: Documentation/security/self-protection.rst
* Reporting Vulnerabilities: Documentation/process/security-bugs.rst
* CVE Procedures: Documentation/process/cve.rst
* Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst
* Security Features: Documentation/userspace-api/seccomp_filter.rst

Backport/Maintenance Engineer
-----------------------------

Maintain and stabilize kernel versions:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* Backporting Guide: Documentation/process/backporting.rst
* Applying Patches: Documentation/process/applying-patches.rst
* Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git for Maintainers: Documentation/maintainer/configure-git.rst

System Administrator
--------------------

Configure, tune, and troubleshoot Linux systems:

* Admin Guide: Documentation/admin-guide/index.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst
* Tracing/Debugging: Documentation/trace/index.rst
* Performance Security: Documentation/admin-guide/perf-security.rst
* Hardware Monitoring: Documentation/hwmon/index.rst

Maintainer
----------

Lead kernel subsystems and manage contributions:

* Maintainer Handbook: Documentation/maintainer/index.rst
* Pull Requests: Documentation/maintainer/pull-requests.rst
* Managing Patches: Documentation/maintainer/modifying-patches.rst
* Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst
* Development Process: Documentation/process/maintainer-handbooks.rst
* Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git Configuration: Documentation/maintainer/configure-git.rst

Hardware Vendor
---------------

Write drivers and support new hardware:

* Driver API Guide: Documentation/driver-api/index.rst
* Driver Model: Documentation/driver-api/driver-model/driver.rst
* Device Drivers: Documentation/driver-api/infrastructure.rst
* Bus Types: Documentation/driver-api/driver-model/bus.rst
* Device Tree Bindings: Documentation/devicetree/bindings/
* Power Management: Documentation/driver-api/pm/index.rst
* DMA API: Documentation/core-api/dma-api.rst

Distribution Maintainer
-----------------------

Package and distribute the kernel:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* ABI Documentation: Documentation/ABI/README
* Kernel Configuration: Documentation/kbuild/kconfig.rst
* Module Signing: Documentation/admin-guide/module-signing.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst

AI Coding Assistant
-------------------

CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and
follow the AI coding assistants documentation before contributing to the Linux
kernel:

* Documentation/process/coding-assistants.rst

This documentation contains essential requirements about licensing, attribution,
and the Developer Certificate of Origin that all AI tools must comply with.


Communication and Support
=========================

* Mailing Lists: https://lore.kernel.org/
* IRC: #kernelnewbies on irc.oftc.net
* Bugzilla: https://bugzilla.kernel.org/
* MAINTAINERS file: Lists subsystem maintainers and mailing lists
* Email Clients: Documentation/process/email-clients.rst