From 106b4a2a78b2a2f14885604891957b84bba502db Mon Sep 17 00:00:00 2001 From: Adrian Betschart Date: Fri, 11 Sep 2026 17:13:14 +0200 Subject: drm/amd/display: Try RGB before YCbCr 4:4:4 in stream validation amdgpu_dm_create_validate_stream_for_sink() walks encoding_order[] and uses the first encoding that validates. YCbCr 4:4:4 is listed before RGB, so an HDMI sink that advertises 4:4:4 gets YCbCr 4:4:4 whenever the "color format" property is left at AUTO, even though RGB fits the same link. That contradicts the documented AUTO behaviour for HDMI in enum drm_connector_color_format (RGB, falling back to YCbCr 4:2:0 only when the bandwidth is not available or the mode is 4:2:0-only), which the amdgpu implementation of the property also describes. It also leaves the "Broadcast RGB" property without effect on such sinks, since the quantization range it selects only applies to RGB output. Try RGB first. The mask still holds every encoding the sink supports, so a mode that cannot carry RGB falls back exactly as before. For reference, v7.2 picked RGB here unless YCbCr 4:4:4 was forced through debugfs, while earlier kernels picked YCbCr 4:4:4 for any HDMI sink that advertised it. Fixes: 0b0ff65d3ca1 ("drm/amd/display: Refactor stream validation") Suggested-by: Adolfo Rodrigues Assisted-by: Claude Code:claude-fable-5-1 Signed-off-by: Adrian Betschart Reviewed-by: Fangzhi Zuo Tested-by: Adolfo Rodrigues Tested-by: Daniel Wheeler Signed-off-by: Alex Deucher (cherry picked from commit 7de432bc753133764dc40d37f9388da56de251e7) --- Documentation/process/programming-language.rst | 58 ++++++++++++++++++++++++++ 1 file changed, 58 insertions(+) create mode 100644 Documentation/process/programming-language.rst (limited to 'Documentation/process/programming-language.rst') diff --git a/Documentation/process/programming-language.rst b/Documentation/process/programming-language.rst new file mode 100644 index 000000000..c18e307cc --- /dev/null +++ b/Documentation/process/programming-language.rst @@ -0,0 +1,58 @@ +.. _programming_language: + +Programming Language +==================== + +The Linux kernel is written in the C programming language [c-language]_. +More precisely, it is typically compiled with ``gcc`` [gcc]_ +under ``-std=gnu11`` [gcc-c-dialect-options]_: the GNU dialect of ISO C11. +``clang`` [clang]_ is also supported; see documentation on +:ref:`Building Linux with Clang/LLVM `. + +This dialect contains many extensions to the language [gnu-extensions]_, +and many of them are used within the kernel as a matter of course. + +Attributes +---------- + +One of the common extensions used throughout the kernel are attributes +[gcc-attribute-syntax]_. Attributes allow to introduce +implementation-defined semantics to language entities (like variables, +functions or types) without having to make significant syntactic changes +to the language (e.g. adding a new keyword) [n2049]_. + +In some cases, attributes are optional (i.e. a compiler not supporting them +should still produce proper code, even if it is slower or does not perform +as many compile-time checks/diagnostics). + +The kernel defines pseudo-keywords (e.g. ``__pure``) instead of using +directly the GNU attribute syntax (e.g. ``__attribute__((__pure__))``) +in order to feature detect which ones can be used and/or to shorten the code. + +Please refer to ``include/linux/compiler_attributes.h`` for more information. + +Rust +---- + +The kernel has support for the Rust programming language +[rust-language]_ under ``CONFIG_RUST``. It is compiled with ``rustc`` [rustc]_ +under ``--edition=2021`` [rust-editions]_. Editions are a way to introduce +small changes to the language that are not backwards compatible. + +On top of that, some unstable features [rust-unstable-features]_ are used in +the kernel. Unstable features may change in the future, thus it is an important +goal to reach a point where only stable features are used. + +Please refer to Documentation/rust/index.rst for more information. + +.. [c-language] http://www.open-std.org/jtc1/sc22/wg14/www/standards +.. [gcc] https://gcc.gnu.org +.. [clang] https://clang.llvm.org +.. [gcc-c-dialect-options] https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html +.. [gnu-extensions] https://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html +.. [gcc-attribute-syntax] https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html +.. [n2049] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2049.pdf +.. [rust-language] https://www.rust-lang.org +.. [rustc] https://doc.rust-lang.org/rustc/ +.. [rust-editions] https://doc.rust-lang.org/edition-guide/editions/ +.. [rust-unstable-features] https://github.com/Rust-for-Linux/linux/issues/2 -- cgit v1.3.1