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Alexey Charkov 5814788834 clk: rockchip: Fractional PLL coefficient on RK3588/RK3576 is two's complement
When the PLL rates table was first committed for RK3588 (and later reused
for RK3576), the fractional PLL coefficient was defined as an unsigned
value, while the TRM clearly states that it is a two's complement 16-bit
value.

Treating the fractional PLL coefficient as unsigned in rate recalculation
results in a kernel-visible rate which deviates from what the hardware
actually generates by Fin / (p * 2^s), or 2 MHz for the two affected table
entries.

Rockchip's downstream kernel later revised the fractional PLL code [1] to
account for the two's complement nature of the coefficient, but that
change wasn't upstreamed.

Change the PLL table definition to use two's complement for the
fractional coefficient and update its users accordingly.

Note that a negative fractional coefficient is meant to be subtracted from
the next larger integer multiplier, so the m values in the table are
also adjusted accordingly for the two negative-k entries.

Rockchip's downstream commit introducing the two's complement logic for k
also does unrelated tweaks to the PLL parameters which are not explained
by the switch to the two's complement, so they are not replicated here.
If any of the parameters prove to need further tweaks (e.g. for precision
or jitter) that would better be done in targeted follow-up commits.

Fractional PLL rates don't seem to be used by any current mainline
consumers, so this is purely a correctness fix. It will also be important
to properly support DisplayPort output going forward, as the video output
controller derives its pixel clock from system PLLs with no dedicated PHY
PLL option for DP unlike HDMI, and some display modes are only achievable
using fractional PLL rates.

Link: 7a72bc05dc [1]
Fixes: f1c506d152 ("clk: rockchip: add clock controller for the RK3588")
Fixes: cc40f5baa9 ("clk: rockchip: Add clock controller for the RK3576")
Signed-off-by: Alexey Charkov <alchark@flipper.net>
Link: https://patch.msgid.link/20260723-rk3588-fracpll-v2-2-3adfb9dda235@flipper.net
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
History 2026-07-28 21:32:30 +02:00
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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/


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============

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* New Kernel Developer - Getting started with kernel development
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* 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
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---------------

Security documentation and hardening guides:

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* LSM Development: Documentation/security/lsm-development.rst
* Self Protection: Documentation/security/self-protection.rst
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* 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

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--------------------

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
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* Hardware Monitoring: Documentation/hwmon/index.rst

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----------

Lead kernel subsystems and manage contributions:

* Maintainer Handbook: Documentation/maintainer/index.rst
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---------------

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* 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.


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=========================

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