d8f5613c5c
[ Upstream commit 4dd432d985ef258e3bc436e568fba4b987b59171 ]
Reconfiguring the clock divider to the exact same value is observed
on an i.MX8MN to often cause a longer than usual clock pause, probably
because the divider restarts counting whenever the register is rewritten.
This issue doesn't show up normally, because the clock framework will
take care to not call set_rate when the clock rate is the same.
However, when we reconfigure an upstream clock, the common code will
call set_rate with the newly calculated rate on all children, e.g.:
- sai5 is running normally and divides Audio PLL out by 16.
- Audio PLL rate is increased by 32Hz (glitch-free kdiv change)
- rates for children are recalculated and rates are set recursively
- imx8m_clk_composite_divider_set_rate(sai5) is called with
32/16 = 2Hz more
- imx8m_clk_composite_divider_set_rate computes same divider as before
- divider register is written, so it restarts counting from zero and
MCLK is briefly paused, so instead of e.g. 40ns, MCLK is low for 120ns.
Some external clock consumers can be upset by such unexpected clock pauses,
so let's make sure we only rewrite the divider value when the value to be
written is actually different.
Fixes:
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|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| 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.