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Gabor Juhos d98f6fcec6
i2c: pxa: handle 'Early Bus Busy' condition on Armada 3700
Under some circumstances I2C recovery fails on Armada 3700. At least
on the Methode uDPU board, removing and replugging an SFP module fails
often, like this:

  [   36.953127] sfp sfp-eth1: module removed
  [   38.468549] i2c i2c-1: i2c_pxa: timeout waiting for bus free
  [   38.486960] sfp sfp-eth1: module MENTECHOPTO      POS22-LDCC-KR    rev 1.0  sn MNC208U90009     dc 200828
  [   38.496867] mvneta d0040000.ethernet eth1: unsupported SFP module: no common interface modes
  [   38.521448] hwmon hwmon2: temp1_input not attached to any thermal zone
  [   39.249196] sfp sfp-eth1: module removed
  ...
  [  292.568799] sfp sfp-eth1: please wait, module slow to respond
  ...
  [  625.208814] sfp sfp-eth1: failed to read EEPROM: -EREMOTEIO

Note that the 'unsupported SFP module' messages are not relevant. The
module is used only for testing the I2C recovery funcionality, because
the error can be triggered easily with this specific one.

Enabling debug in the i2c-pxa driver reveals the following:

  [   82.034678] sfp sfp-eth1: module removed
  [   90.008654] i2c i2c-1: slave_0x50 error: timeout with active message
  [   90.015112] i2c i2c-1: msg_num: 2 msg_idx: 0 msg_ptr: 0
  [   90.020464] i2c i2c-1: IBMR: 00000003 IDBR: 000000a0 ICR: 000007e0 ISR: 00000802
  [   90.027906] i2c i2c-1: log:
  [   90.030787]

This continues until the retries are exhausted ...

  [  110.192489] i2c i2c-1: slave_0x50 error: exhausted retries
  [  110.198012] i2c i2c-1: msg_num: 2 msg_idx: 0 msg_ptr: 0
  [  110.203323] i2c i2c-1: IBMR: 00000003 IDBR: 000000a0 ICR: 000007e0 ISR: 00000802
  [  110.210810] i2c i2c-1: log:
  [  110.213633]

... then the whole sequence starts again ...

  [  115.368641] i2c i2c-1: slave_0x50 error: timeout with active message

... while finally the SFP core gives up:

  [  671.975258] sfp sfp-eth1: failed to read EEPROM: -EREMOTEIO

When we analyze the log, it can be seen that bit 1 and 11 is set in the
ISR (Interface Status Register). Bit 1 indicates the ACK/NACK status, but
the purpose of bit 11 is not documented in the driver code unfortunately.

The 'Functional Specification' document of the Armada 3700 SoCs family
however says that this bit indicates an 'Early Bus Busy' condition. The
document also notes that whenever this bit is set, it is not possible to
initiate a transaction on the I2C bus. The observed behaviour corresponds
to this statement.

Unfortunately, I2C recovery does not help as it never runs in this
special case. Although the driver checks the busyness of the bus at
several places, but since it does not consider the A3700 specific bit
in these checks it can't determine the actual status of the bus correctly
which results in the errors above.

In order to fix the problem, add a new member to struct 'i2c_pxa' to
store a controller specific bitmask containing the bits indicating the
busy status, and use that in the code while checking the actual status
of the bus. This ensures that the correct status can be determined on
the Armada 3700 based devices without causing functional changes on
devices based on other SoCs.

With the change applied, the driver detects the busy condition, and runs
the recovery process:

  [  742.617312] i2c i2c-1: state:i2c_pxa_wait_bus_not_busy:449: ISR=00000802, ICR=000007e0, IBMR=03
  [  742.626099] i2c i2c-1: i2c_pxa: timeout waiting for bus free
  [  742.631933] i2c i2c-1: recovery: resetting controller, ISR=0x00000802
  [  742.638421] i2c i2c-1: recovery: IBMR 0x00000003 ISR 0x00000000

This clears the EBB bit in the ISR register, so it makes it possible to
initiate transactions on the I2C bus again.

After this patch, the SFP module used for testing can be removed and
replugged numerous times without causing the error described at the
beginning. Previously, the error happened after a few such attempts.

The patch has been tested also with the following kernel versions:
5.10.251, 5.15.201, 6.1.164, 6.6.127, 6.12.74, 6.14.11, 6.15.10, 6.16.1,
6.18.13, 6.19.3
It improves recovery on all of them.

Signed-off-by: Gabor Juhos <j4g8y7@gmail.com>
Reviewed-by: Imre Kaloz <kaloz@openwrt.org>
Tested-by: Robert Marko <robert.marko@sartura.hr>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/20260226-i2c-pxa-fix-i2c-communication-v4-2-797a091dae87@gmail.com
History 2026-04-15 00:13:33 +02:00
arch Fix incorrect hardware errors reported on Zen3 CPUs, such 2026-04-12 08:27:09 -07:00
block block-7.0-20260305 2026-03-06 08:36:18 -08:00
certs Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
crypto This push contains the following changes: 2026-04-12 08:11:02 -07:00
Documentation RISC-V updates for v7.0-rc8 2026-04-10 17:27:08 -07:00
drivers i2c: pxa: handle 'Early Bus Busy' condition on Armada 3700 2026-04-15 00:13:33 +02:00
fs vfs-7.0-rc8.fixes 2026-04-10 08:40:49 -07:00
include Two fixes for the time/timers subsystem: 2026-04-12 10:01:55 -07:00
init hardening fixes for v7.0-rc6 2026-03-25 14:47:18 -07:00
io_uring io_uring-7.0-20260403 2026-04-03 11:58:04 -07:00
ipc Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
kernel workqueue: Fixes for v7.0-rc7 2026-04-12 10:42:40 -07:00
lib kernfs: pass struct ns_common instead of const void * for namespace tags 2026-04-09 14:36:52 +02:00
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 8 hotfixes. All are cc:stable and 7 are for MM. 2026-04-07 10:24:44 -07:00
net vfs-7.0-rc8.fixes 2026-04-10 08:40:49 -07:00
rust rust: regulator: do not assume that regulator_get() returns non-null 2026-03-24 13:08:21 +00:00
samples Landlock fix for v7.0-rc6 2026-03-26 12:03:37 -07:00
scripts modpost: Declare extra_warn with unused attribute 2026-03-30 07:45:34 +02:00
security Landlock fix for v7.0-rc6 2026-03-26 12:03:37 -07:00
sound ASoC: Fixes for v7.0 2026-04-09 07:00:53 +02:00
tools RISC-V updates for v7.0-rc8 2026-04-10 17:27:08 -07:00
usr kbuild: uapi: drop dependency on CC_CAN_LINK 2026-01-16 15:02:11 -07:00
virt KVM generic changes for 7.0 2026-03-11 18:01:55 +01:00
.clang-format Devicetree updates for v7.0: 2026-02-11 18:27:08 -08:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.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 rust: kbuild: add proc macro library support 2025-11-24 17:15:36 +01:00
.mailmap MAINTAINERS, mailmap: Change Ulf Hansson's email 2026-04-07 14:17:48 +02:00
.pylintrc docs: Move the python libraries to tools/lib/python 2025-11-18 09:22:40 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: remove Thomas Falcon from IBM ibmvnic 2026-03-05 07:35:45 -08:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS spi: Fixes for v7.0 2026-04-11 12:49:21 -07:00
Makefile Linux 7.0 2026-04-12 13:48:06 -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
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* 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.


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

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