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Currently, a timeout error could happen at a repeated START condition.
For a (non-repeated) START condition, the controller starts sending
data when the UNIPHIER_FI2C_CR_STA bit is set. However, for a repeated
START condition, the hardware starts running when the slave address is
written to the TX FIFO - the write to the UNIPHIER_FI2C_CR register is
actually unneeded.
Because the hardware is already running before the IRQ is enabled for
a repeated START, the driver may miss the IRQ event. In most cases,
this problem does not show up since modern CPUs are much faster than
the I2C transfer. However, it is still possible that a context switch
happens after the controller starts, but before the IRQ register is
set up.
To fix this,
- Do not write UNIPHIER_FI2C_CR for repeated START conditions.
- Enable IRQ *before* writing the slave address to the TX FIFO.
- Disable IRQ for the current CPU while queuing up the TX FIFO;
If the CPU is interrupted by some task, the interrupt handler
might be invoked due to the empty TX FIFO before completing the
setup.
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.