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Vidya Srinivas f61289af26
drm/i915/display: Fix NV12 ceiling division for bigjoiner case
Commit 16df4cc63c ("drm/i915/display: Use ceiling division for NV12
UV surface offset calculation") computes the UV (chroma) surface
start/size as ceiling(half of Y plane start/size) directly from the
U16.16 fixed-point source rectangle:

        x = fp_16_16_to_int_ceil(fp_16_16_div2(src.x1));

For a single pipe the source coordinates are integers, so this is
correct.
(UV start = ceiling(half of Y plane start)).

With bigjoiner + a plane scaler the picture changes. The pipe boundary
is a fixed integer destination pixel, but the plane's position and the
scaler ratio are arbitrary, so drm_rect_clip_scaled() maps the seam back
to a *fractional* per-pipe source. For a 1280->2407 upscaled NV12 plane
crossing the seam:

        master src: width = 1204 * 1280/2407 = 640.265899, x1 = 0
        joiner src: width = 1203 * 1280/2407 = 639.734115, x1 = 640.265884

The luma path floors this to an integer (src.x1 >> 16 = 640), but the
UV path takes ceiling(640.265884 / 2) = ceil(320.13) = 321. The Y plane
then starts at column 640 while the UV plane starts at 321*2 = 642,
pushing the chroma read one column past the 640-wide chroma surface on
the joiner secondary:

        [CRTC:382:pipe C] PLANE ATS fault
        [CRTC:382:pipe C][PLANE:267:plane 1C] fault (CTL=0x81009400, ...)

The spec "Y plane start" is the integer pixel the luma surface actually
programs (640), not the pre-floor fixed-point value (640.27). Convert
the Y plane start/size to integer first - matching skl_check_main_surface()
- and then apply the ceiling. This is a no-op for the integer (non-joiner)
case and yields the correct, in-bounds chroma offset for the fractional
joiner seam:

                     before fix      after fix
        master 1B:   x=0  w=321      x=0   w=320   -> [0, 320)
        slave  1C:   x=321 w=320     x=320 w=320   -> [320, 640)

The two halves now tile the 640-wide chroma plane exactly and the ATS
fault is gone.

Assisted-by: GitHub-Copilot:Claude-Opus-4.8
Fixes: 16df4cc63c ("drm/i915/display: Use ceiling division for NV12 UV surface offset calculation")
Signed-off-by: Vidya Srinivas <vidya.srinivas@intel.com>
Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Link: https://patch.msgid.link/20260618181837.687302-1-vidya.srinivas@intel.com
(cherry picked from commit 0c59cc78241c10e5f02d92b28d811b0435e706a7)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
2026-07-14 09:38:19 -04:00
arch s390 updates for 7.2-rc3 2026-07-12 11:38:00 -07:00
block block: remove redundant GD_NEED_PART_SCAN in add_disk_final() 2026-07-10 09:08:50 -06:00
certs treewide: fix indentation and whitespace in Kconfig files 2026-05-28 21:24:42 -07:00
crypto mm.git review status for mm-hotfixes-stable..mm-nonmm-stable 2026-06-21 13:20:19 -07:00
Documentation USB fixes for 7.2-rc3 2026-07-12 12:12:41 -07:00
drivers drm/i915/display: Fix NV12 ceiling division for bigjoiner case 2026-07-14 09:38:19 -04:00
fs Misc x86 fixes: 2026-07-11 10:09:23 -07:00
include Android/IIO bugfixes for 7.2-rc3 2026-07-12 12:37:28 -07:00
init mm.git review status for mm-hotfixes-stable..mm-nonmm-stable 2026-06-21 13:20:19 -07:00
io_uring io_uring-7.2-20260710 2026-07-11 09:24:38 -07:00
ipc kernel-7.2-rc1.misc 2026-06-15 03:05:50 +05:30
kernel tracing fixes for 7.2: 2026-07-12 09:46:37 -07:00
lib tracing: Prevent out-of-bounds read in glob matching 2026-07-07 10:42:28 -04:00
LICENSES LICENSES: Add modern form of the LGPL-2.1 tags to the usage guide section 2025-10-22 07:58:19 +02:00
mm mm: do file ownership checks with the proper mount idmap 2026-07-01 19:02:56 -07:00
net NFS Client Bugfixes for Linux 7.2-rc3 2026-07-10 18:15:26 -07:00
rust Rust changes for v7.2 (addendum) 2026-06-24 15:11:08 -07:00
samples tracing fixes for 7.2: 2026-07-12 09:46:37 -07:00
scripts scripts/sorttable: Handle RISC-V patchable ftrace entries 2026-06-25 13:15:03 -06:00
security selinux/stable-7.2 PR 20260710 2026-07-10 18:59:29 -07:00
sound sound fixes for 7.2-rc2 2026-07-05 05:26:45 -10:00
tools USB fixes for 7.2-rc3 2026-07-12 12:12:41 -07:00
usr kbuild: uapi: also test UAPI headers against C++ compilers 2026-03-25 13:24:42 +01:00
virt s390: 2026-06-25 10:21:13 -07:00
.clang-format clang-format: fix formatting of guard() and scoped_guard() statements 2026-05-28 21:24:41 -07:00
.clippy.toml rust: bump Clippy's MSRV and clean incompatible_msrv allows 2026-04-07 09:51:39 +02:00
.cocciconfig
.editorconfig editorconfig: add rst extension 2026-01-26 19:07:09 -08:00
.get_maintainer.ignore .get_maintainer.ignore: add myself 2026-04-02 16:48:25 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore SPDX patches for 7.2-rc1 2026-06-22 12:06:22 -07:00
.mailmap 20 hotfixes. 17 are for MM. 12 are cc:stable and the remaining 8 2026-07-06 18:51:36 -07:00
.pylintrc docs: Move the python libraries to tools/lib/python 2025-11-18 09:22:40 -07:00
.rustfmt.toml
COPYING
CREDITS mm.git review status for mm-hotfixes-stable..mm-nonmm-stable 2026-06-21 13:20:19 -07:00
Kbuild checksyscalls: move instance functionality into generic code 2026-04-05 09:21:32 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS USB fixes for 7.2-rc3 2026-07-12 12:12:41 -07:00
Makefile Linux 7.2-rc3 2026-07-12 14:16:39 -07:00
README docs: add AI Coding Assistants documentation 2026-01-06 14:55:06 -07:00

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