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After the power-down bit is cleared, the chip internally triggers a
global reset. According to the KSZ9031 documentation, we have to wait at
least 1ms for the reset to finish.
If the chip is accessed during reset, read will return 0xffff, while
write will be ignored. Depending on the system performance and MDIO bus
speed, we may or may not run in to this issue.
This bug was discovered on an iMX6QP system with KSZ9031 PHY and
attached PHY interrupt line. If IRQ was used, the link status update was
lost. In polling mode, the link status update was always correct.
The investigation showed, that during a read-modify-write access, the
read returned 0xffff (while the chip was still in reset) and
corresponding write hit the chip _after_ reset and triggered (due to the
0xffff) another reset in an undocumented bit (register 0x1f, bit 1),
resulting in the next write being lost due to the new reset cycle.
This patch fixes the issue by adding a 1...2 ms sleep after the
genphy_resume().
Fixes:
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| 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.
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.