diff options
Diffstat (limited to 'Documentation/clk.txt')
| -rw-r--r-- | Documentation/clk.txt | 99 |
1 files changed, 76 insertions, 23 deletions
diff --git a/Documentation/clk.txt b/Documentation/clk.txt index 6f68ba0d1e0..1fee72f4d33 100644 --- a/Documentation/clk.txt +++ b/Documentation/clk.txt @@ -68,12 +68,27 @@ the operations defined in clk.h: int (*is_enabled)(struct clk_hw *hw); unsigned long (*recalc_rate)(struct clk_hw *hw, unsigned long parent_rate); - long (*round_rate)(struct clk_hw *hw, unsigned long, - unsigned long *); + long (*round_rate)(struct clk_hw *hw, + unsigned long rate, + unsigned long *parent_rate); + long (*determine_rate)(struct clk_hw *hw, + unsigned long rate, + unsigned long *best_parent_rate, + struct clk **best_parent_clk); int (*set_parent)(struct clk_hw *hw, u8 index); u8 (*get_parent)(struct clk_hw *hw); - int (*set_rate)(struct clk_hw *hw, unsigned long); + int (*set_rate)(struct clk_hw *hw, + unsigned long rate, + unsigned long parent_rate); + int (*set_rate_and_parent)(struct clk_hw *hw, + unsigned long rate, + unsigned long parent_rate, + u8 index); + unsigned long (*recalc_accuracy)(struct clk_hw *hw, + unsigned long parent_accuracy); void (*init)(struct clk_hw *hw); + int (*debug_init)(struct clk_hw *hw, + struct dentry *dentry); }; Part 3 - hardware clk implementations @@ -179,26 +194,30 @@ mandatory, a cell marked as "n" implies that either including that callback is invalid or otherwise unnecessary. Empty cells are either optional or must be evaluated on a case-by-case basis. - clock hardware characteristics - ----------------------------------------------------------- - | gate | change rate | single parent | multiplexer | root | - |------|-------------|---------------|-------------|------| -.prepare | | | | | | -.unprepare | | | | | | - | | | | | | -.enable | y | | | | | -.disable | y | | | | | -.is_enabled | y | | | | | - | | | | | | -.recalc_rate | | y | | | | -.round_rate | | y | | | | -.set_rate | | y | | | | - | | | | | | -.set_parent | | | n | y | n | -.get_parent | | | n | y | n | - | | | | | | -.init | | | | | | - ----------------------------------------------------------- + clock hardware characteristics + ----------------------------------------------------------- + | gate | change rate | single parent | multiplexer | root | + |------|-------------|---------------|-------------|------| +.prepare | | | | | | +.unprepare | | | | | | + | | | | | | +.enable | y | | | | | +.disable | y | | | | | +.is_enabled | y | | | | | + | | | | | | +.recalc_rate | | y | | | | +.round_rate | | y [1] | | | | +.determine_rate | | y [1] | | | | +.set_rate | | y | | | | + | | | | | | +.set_parent | | | n | y | n | +.get_parent | | | n | y | n | + | | | | | | +.recalc_accuracy| | | | | | + | | | | | | +.init | | | | | | + ----------------------------------------------------------- +[1] either one of round_rate or determine_rate is required. Finally, register your clock at run-time with a hardware-specific registration function. This function simply populates struct clk_foo's @@ -242,3 +261,37 @@ 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. |