mutual exculsion between clk_prepare_enable /clk_disable_unprepareand clk_set_parent

From: Xiaoguang Chen
Date: Wed Jan 22 2014 - 01:03:34 EST

Hi, Mike

We met a issue between clk_prepare_enable /clk_disable_unprepare and

As we know, clk preprare/unprare will grab preprare lock, and clk
enable/disable will grab enable lock. clk_set_parent will grab prepare

but there is no lock protection in clk_prepare_enable /clk_disable_unprepare,
for example, in clk_disable_unprepare, it is expended as clk_disable +

and if below condition occurs, there will be problem
thread1 thread 2
call clk_disable_unprepare
1) clk_disable
get enable lock
release enable lock

call clk_set_parent
get prepare lock
set clock's
parent to another parent
release prepare lock

2) clk_unprepare
get prepare lock
unprepare parent clock <<--------------
release prepare lock

In above sequence, After thread 1 call clock disable, thread 2 change
clk's parent to another clock, then in thread1 step2, it will
unprepare clk's new parent, but not old parent, this will cause old
parent is not unprepared, but new parent is unprepared even when it is
not prepared yet.

So How can we use this API: clk_prepare_enable and clk_disable_unprepare ?
Should we add lock to protect this API, if we get a prepare lock
inside this API, like
clk_disable_unprepare ()

is above sequence ok? if so, I can provide a patch for this.

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