Hi Stephen,
Le sam. 13 mars 2021 à 14:28, Stephen Boyd <sboyd@xxxxxxxxxx> a écrit
:
Quoting Paul Cercueil (2021-03-07 09:07:41)
The purpose of this function is to be used along with the notifier
mechanism.
When a parent clock can see its rate externally changed at any
moment,
and a driver needs a specific clock rate to function, it can
register a
notifier on the parent clock, and call clk_set_rate() on the base
clock
to adjust its frequency according to the new parent clock.
Can the driver use the rate locking mechanism to get a certain rate
instead of registering for notifiers and trying to react to changes?
You mean with clk_rate_exclusive_get()? That sounds like a good idea,
but what would happen when a different driver calls the non-exclusive
clk_set_rate() on this clock (or the parent), would it return -EBUSY,
lock on a mutex? ...
Cheers,
-Paul
This works fine, until the base clock has the CLK_SET_RATE_PARENT
flag
set. In that case, calling clk_set_rate() on the base clock will
call
clk_set_rate() on the parent clock, which will trigger the notifier
again, and we're in a loop.
For that reason, we need to register the notifier on the parent
clock of
the first ancestor of the base clock that will effectively modify
its
rate when clk_set_rate() is called, which we can now obtain with
clk_get_first_to_set_rate().
Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
