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author | Michael Ellerman <mpe@ellerman.id.au> | 2017-07-31 12:20:29 +0200 |
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committer | Michael Ellerman <mpe@ellerman.id.au> | 2017-07-31 12:20:29 +0200 |
commit | bb272221e9db79f13d454e1f3fb6b05013be985e (patch) | |
tree | 36f4acc50e3fabac71fadd34c720c0a6011db470 /Documentation/clk.txt | |
parent | powerpc/powernv/pci: Return failure for some uses of dma_set_mask() (diff) | |
parent | Linux v4.13-rc1 (diff) | |
download | linux-bb272221e9db79f13d454e1f3fb6b05013be985e.tar.xz linux-bb272221e9db79f13d454e1f3fb6b05013be985e.zip |
Merge tag 'v4.13-rc1' into fixes
The fixes branch is based off a random pre-rc1 commit, because we had
some fixes that needed to go in before rc1 was released.
However we now need to fix some code that went in after that point, but
before rc1, so merge rc1 to get that code into fixes so we can fix it!
Diffstat (limited to 'Documentation/clk.txt')
-rw-r--r-- | Documentation/clk.txt | 189 |
1 files changed, 106 insertions, 83 deletions
diff --git a/Documentation/clk.txt b/Documentation/clk.txt index 22f026aa2f34..be909ed45970 100644 --- a/Documentation/clk.txt +++ b/Documentation/clk.txt @@ -1,12 +1,16 @@ - The Common Clk Framework - Mike Turquette <mturquette@ti.com> +======================== +The Common Clk Framework +======================== + +:Author: Mike Turquette <mturquette@ti.com> This document endeavours to explain the common clk framework details, and how to port a platform over to this framework. It is not yet a detailed explanation of the clock api in include/linux/clk.h, but perhaps someday it will include that information. - Part 1 - introduction and interface split +Introduction and interface split +================================ The common clk framework is an interface to control the clock nodes available on various devices today. This may come in the form of clock @@ -35,10 +39,11 @@ is defined in struct clk_foo and pointed to within struct clk_core. This allows for easy navigation between the two discrete halves of the common clock interface. - Part 2 - common data structures and api +Common data structures and api +============================== Below is the common struct clk_core definition from -drivers/clk/clk.c, modified for brevity: +drivers/clk/clk.c, modified for brevity:: struct clk_core { const char *name; @@ -59,7 +64,7 @@ struct clk. That api is documented in include/linux/clk.h. Platforms and devices utilizing the common struct clk_core use the struct clk_ops pointer in struct clk_core to perform the hardware-specific parts of -the operations defined in clk-provider.h: +the operations defined in clk-provider.h:: struct clk_ops { int (*prepare)(struct clk_hw *hw); @@ -95,19 +100,20 @@ the operations defined in clk-provider.h: struct dentry *dentry); }; - Part 3 - hardware clk implementations +Hardware clk implementations +============================ The strength of the common struct clk_core comes from its .ops and .hw pointers which abstract the details of struct clk from the hardware-specific bits, and vice versa. To illustrate consider the simple gateable clk implementation in -drivers/clk/clk-gate.c: +drivers/clk/clk-gate.c:: -struct clk_gate { - struct clk_hw hw; - void __iomem *reg; - u8 bit_idx; - ... -}; + struct clk_gate { + struct clk_hw hw; + void __iomem *reg; + u8 bit_idx; + ... + }; struct clk_gate contains struct clk_hw hw as well as hardware-specific knowledge about which register and bit controls this clk's gating. @@ -115,7 +121,7 @@ Nothing about clock topology or accounting, such as enable_count or notifier_count, is needed here. That is all handled by the common framework code and struct clk_core. -Let's walk through enabling this clk from driver code: +Let's walk through enabling this clk from driver code:: struct clk *clk; clk = clk_get(NULL, "my_gateable_clk"); @@ -123,70 +129,71 @@ Let's walk through enabling this clk from driver code: clk_prepare(clk); clk_enable(clk); -The call graph for clk_enable is very simple: +The call graph for clk_enable is very simple:: -clk_enable(clk); - clk->ops->enable(clk->hw); - [resolves to...] - clk_gate_enable(hw); - [resolves struct clk gate with to_clk_gate(hw)] - clk_gate_set_bit(gate); + clk_enable(clk); + clk->ops->enable(clk->hw); + [resolves to...] + clk_gate_enable(hw); + [resolves struct clk gate with to_clk_gate(hw)] + clk_gate_set_bit(gate); -And the definition of clk_gate_set_bit: +And the definition of clk_gate_set_bit:: -static void clk_gate_set_bit(struct clk_gate *gate) -{ - u32 reg; + static void clk_gate_set_bit(struct clk_gate *gate) + { + u32 reg; - reg = __raw_readl(gate->reg); - reg |= BIT(gate->bit_idx); - writel(reg, gate->reg); -} + reg = __raw_readl(gate->reg); + reg |= BIT(gate->bit_idx); + writel(reg, gate->reg); + } -Note that to_clk_gate is defined as: +Note that to_clk_gate is defined as:: -#define to_clk_gate(_hw) container_of(_hw, struct clk_gate, hw) + #define to_clk_gate(_hw) container_of(_hw, struct clk_gate, hw) This pattern of abstraction is used for every clock hardware representation. - Part 4 - supporting your own clk hardware +Supporting your own clk hardware +================================ When implementing support for a new type of clock it is only necessary to -include the following header: +include the following header:: -#include <linux/clk-provider.h> + #include <linux/clk-provider.h> To construct a clk hardware structure for your platform you must define -the following: +the following:: -struct clk_foo { - struct clk_hw hw; - ... hardware specific data goes here ... -}; + struct clk_foo { + struct clk_hw hw; + ... hardware specific data goes here ... + }; To take advantage of your data you'll need to support valid operations -for your clk: +for your clk:: -struct clk_ops clk_foo_ops { - .enable = &clk_foo_enable; - .disable = &clk_foo_disable; -}; + struct clk_ops clk_foo_ops { + .enable = &clk_foo_enable; + .disable = &clk_foo_disable; + }; -Implement the above functions using container_of: +Implement the above functions using container_of:: -#define to_clk_foo(_hw) container_of(_hw, struct clk_foo, hw) + #define to_clk_foo(_hw) container_of(_hw, struct clk_foo, hw) -int clk_foo_enable(struct clk_hw *hw) -{ - struct clk_foo *foo; + int clk_foo_enable(struct clk_hw *hw) + { + struct clk_foo *foo; - foo = to_clk_foo(hw); + foo = to_clk_foo(hw); - ... perform magic on foo ... + ... perform magic on foo ... - return 0; -}; + return 0; + }; Below is a matrix detailing which clk_ops are mandatory based upon the hardware capabilities of that clock. A cell marked as "y" means @@ -194,41 +201,56 @@ 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 [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. +.. table:: 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 data and then passes the common struct clk parameters to the framework -with a call to: +with a call to:: -clk_register(...) + clk_register(...) -See the basic clock types in drivers/clk/clk-*.c for examples. +See the basic clock types in ``drivers/clk/clk-*.c`` for examples. - Part 5 - Disabling clock gating of unused clocks +Disabling clock gating of unused clocks +======================================= Sometimes during development it can be useful to be able to bypass the default disabling of unused clocks. For example, if drivers aren't enabling @@ -239,7 +261,8 @@ are sorted out. To bypass this disabling, include "clk_ignore_unused" in the bootargs to the kernel. - Part 6 - Locking +Locking +======= The common clock framework uses two global locks, the prepare lock and the enable lock. |