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44a9e78f92
The PLL status polling loops in the set_rate callbacks of some PLLs have no timeout detection and may become endless loops when something goes wrong with the PLL. For some PLLs there is already the ktime API based timeout detection, but it will not work in all conditions when .set_rate gets called. In particular, before the clocksource is initialized or when the timekeeping is suspended. This patch adds a common helper with the PLL status bit polling and timeout detection. For conditions where the timekeeping API should not be used a simple readl_relaxed/cpu_relax() busy loop is added with the iterations limit derived from measurements of readl_relaxed() execution time for various PLL types and Exynos SoCs variants. Actual PLL lock time depends on the P divider value, the VCO frequency and a constant PLL type specific LOCK_FACTOR and can be calculated as lock_time = Pdiv * LOCK_FACTOR / VCO_freq For the ktime API use cases a common timeout value of 20 ms is applied for all the PLLs with an assumption that maximum possible value of Pdiv is 64, maximum possible LOCK_FACTOR value is 3000 and minimum VCO frequency is 24 MHz. Link: https://lore.kernel.org/r/20201120155731.26898-1-s.nawrocki@samsung.com Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org> Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com> |
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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.