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All arm64 CPUs feature an architected timer, which offers a relatively
low-latency interface to a per-cpu clocksource and timer. For the most
part, using this interface is a no-brainer, with the exception of SoCs
where it cannot be used to wake up from deep idle state (i.e.
CLOCK_EVT_FEAT_C3STOP is set).
On the contrary, the Exynos MCT is extremely slow to access yet can be
used as a wakeup source. In preparation for using the Exynos MCT as a
potential wakeup timer for the Arm architected timer, reduce its ratings
so that the architected timer is preferred.
This effectively reverts the decision made in 6282edb72b
("clocksource/drivers/exynos_mct: Increase priority over ARM arch timer")
for arm64, as the reasoning for the original change was to work around
a 32-bit SoC design.
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Chanwoo Choi <cw00.choi@samsung.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Will Deacon <will@kernel.org>
Tested-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com> # exynos-5422
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210608154341.10794-2-will@kernel.org
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.