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The SAM9x5 main clock implements a mux with a set_parent hook, but doesn't provide a determine_rate implementation. This is a bit odd, since set_parent() is there to, as its name implies, change the parent of a clock. However, the most likely candidates to trigger that parent change are either the assigned-clock-parents device tree property or a call to clk_set_rate(), with determine_rate() figuring out which parent is the best suited for a given rate. The other trigger would be a call to clk_set_parent(), but it's far less used, and it doesn't look like there's any obvious user for that clock. Similarly, it doesn't look like the device tree using that clock driver uses any of the assigned-clock properties on that clock. So, the set_parent hook is effectively unused, possibly because of an oversight. However, it could also be an explicit decision by the original author to avoid any reparenting but through an explicit call to clk_set_parent(). The latter case would be equivalent to setting the determine_rate implementation to clk_hw_determine_rate_no_reparent(). Indeed, if no determine_rate implementation is provided, clk_round_rate() (through clk_core_round_rate_nolock()) will call itself on the parent if CLK_SET_RATE_PARENT is set, and will not change the clock rate otherwise. And if it was an oversight, then we are at least explicit about our behavior now and it can be further refined down the line. Cc: Alexandre Belloni <alexandre.belloni@bootlin.com> Cc: Claudiu Beznea <claudiu.beznea@microchip.com> Cc: Nicolas Ferre <nicolas.ferre@microchip.com> Cc: linux-arm-kernel@lists.infradead.org Signed-off-by: Maxime Ripard <maxime@cerno.tech> Link: https://lore.kernel.org/r/20221018-clk-range-checks-fixes-v4-9-971d5077e7d2@cerno.tech Signed-off-by: Stephen Boyd <sboyd@kernel.org> |
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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.