clk: ux500: prcmu: Add a determine_rate hook

clk: ux500: prcmu: Add a determine_rate hook

The UX500 PRCMU "clkout" 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 PRCMU binding also allows to specify the default clock parent
through a device tree cell. This will be enforced at prepare time by the
driver.

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.

The result is that the driver relies on prepare to set the default
parent, and thus the set_parent hook is effectively unused by design.

We can make that decision explicit by setting the determine_rate
implementation to clk_hw_determine_rate_no_reparent() that will keep the
same behaviour. 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.

Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: linux-arm-kernel@lists.infradead.org
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20221018-clk-range-checks-fixes-v4-37-971d5077e7d2@cerno.tech
Signed-off-by: Stephen Boyd <sboyd@kernel.org>