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5600722460If IC_EMPTYFIFO_HOLD_MASTER_EN parameter is 0, "Stop" and "Repeated Start"
bits in command register do not exist, thus it is impossible to send
several consecutive write messages in a single hardware batch. The
existing implementation worked with such configuration incorrectly:
all consecutive write messages are joined into a single message without
any Start/Stop or Repeated Start conditions. For example, the following
command:
i2ctransfer -y 0 w1@0x55 0x00 w1@0x55 0x01
does the same as
i2ctransfer -y 0 w2@0x55 0x00 0x01
In i2c_dw_msg_is_valid(), we ensure that we do not have such sequence
of messages requiring a RESTART, aborting the transfer on controller
that cannot emit them explicitly.
This behavior is activated by compatible entries because the state of
the IC_EMPTYFIFO_HOLD_MASTER_EN parameter cannot be detected at runtime.
The new flag emptyfifo_hold_master reflects the state of the parameter,
it is set to true for all controllers except those found in Mobileye
SoCs. For now, the controllers in Mobileye SoCs are the only ones known
to need the workaround. The behavior of the driver is left unmodified
for other controllers.
There is another possible problem with this controller configuration:
When the CPU is putting commands to the FIFO, this process must not be
interrupted because if FIFO buffer gets empty, the controller finishes
the I2C transaction and generates STOP condition on the bus.
If we continue writing the remainder of the message to the FIFO, the
controller will start emitting a new transaction with those data. This
turns a single message into multiple I2C transactions. To protect against
FIFO underrun, two changes are done:
First we flag the interrupt with IRQF_NO_THREAD, to prevent it from
running in a thread on PREEMPT-RT kernel. This ensures that we are
not interrupted when filling the FIFO as it is very time-senstive. For
example, being preempted after writing a single byte in the FIFO with
a 1MHz bus gives us only 18µs before an underrun. DMA would allow us
to keep the interrupt threaded but it is not available on Mobileye SoC
for I2C.
Second in i2c_dw_process_transfer(), we abort if a STOP is detected
while a read or a write is in progress. This can occur when processing
a message larger than the FIFO. In that case the message is processed in
parts, and rely on the TX EMPTY interrupt to refill the FIFO when it gets
below a threshold. If servicing this interrupt is delayed for too long,
it can trigger a FIFO underrun, thus an unwanted STOP.
Originally-by: Dmitry Guzman <dmitry.guzman@mobileye.com>
Signed-off-by: Benoît Monin <benoit.monin@bootlin.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/20260130-i2c-dw-v6-3-08ca1e9ece07@bootlin.com
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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 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 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