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Diffstat (limited to 'Documentation/clk.txt')
| -rw-r--r-- | Documentation/clk.txt | 34 |
1 files changed, 34 insertions, 0 deletions
diff --git a/Documentation/clk.txt b/Documentation/clk.txt index 699ef2a323b1..c9c399af7c08 100644 --- a/Documentation/clk.txt +++ b/Documentation/clk.txt @@ -255,3 +255,37 @@ are sorted out. To bypass this disabling, include "clk_ignore_unused" in the bootargs to the kernel. + + Part 7 - Locking + +The common clock framework uses two global locks, the prepare lock and the +enable lock. + +The enable lock is a spinlock and is held across calls to the .enable, +.disable and .is_enabled operations. Those operations are thus not allowed to +sleep, and calls to the clk_enable(), clk_disable() and clk_is_enabled() API +functions are allowed in atomic context. + +The prepare lock is a mutex and is held across calls to all other operations. +All those operations are allowed to sleep, and calls to the corresponding API +functions are not allowed in atomic context. + +This effectively divides operations in two groups from a locking perspective. + +Drivers don't need to manually protect resources shared between the operations +of one group, regardless of whether those resources are shared by multiple +clocks or not. However, access to resources that are shared between operations +of the two groups needs to be protected by the drivers. An example of such a +resource would be a register that controls both the clock rate and the clock +enable/disable state. + +The clock framework is reentrant, in that a driver is allowed to call clock +framework functions from within its implementation of clock operations. This +can for instance cause a .set_rate operation of one clock being called from +within the .set_rate operation of another clock. This case must be considered +in the driver implementations, but the code flow is usually controlled by the +driver in that case. + +Note that locking must also be considered when code outside of the common +clock framework needs to access resources used by the clock operations. This +is considered out of scope of this document. |