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Documentation: clk: update file names containing referenced structures
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Commit 'b09d6d991' removes include/linux/clk-private.h and
re-arranges the clock related structures contained in it in
different files. The documentation has not been updated
accordingly, thus it wasn't anymore consistent.

Place the structures referenced by Documentation/clk.txt in the
correct files and update their contents to the latest status.

Signed-off-by: Andi Shyti <[email protected]>
[geert: Fix path to clk.c, whitespace, more clk_core, ...]
Signed-off-by: Geert Uytterhoeven <[email protected]>
Signed-off-by: Jonathan Corbet <[email protected]>
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Andi Shyti authored and Jonathan Corbet committed Aug 14, 2016
1 parent a55a51d commit 6203a64
Showing 1 changed file with 22 additions and 20 deletions.
42 changes: 22 additions & 20 deletions Documentation/clk.txt
Original file line number Diff line number Diff line change
Expand Up @@ -31,41 +31,45 @@ serve as a convenient shorthand for the implementation of the
hardware-specific bits for the hypothetical "foo" hardware.

Tying the two halves of this interface together is struct clk_hw, which
is defined in struct clk_foo and pointed to within struct clk. This
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

Below is the common struct clk definition from
include/linux/clk-private.h, modified for brevity:
Below is the common struct clk_core definition from
drivers/clk/clk.c, modified for brevity:

struct clk {
struct clk_core {
const char *name;
const struct clk_ops *ops;
struct clk_hw *hw;
char **parent_names;
struct clk **parents;
struct clk *parent;
struct hlist_head children;
struct hlist_node child_node;
struct module *owner;
struct clk_core *parent;
const char **parent_names;
struct clk_core **parents;
u8 num_parents;
u8 new_parent_index;
...
};

The members above make up the core of the clk tree topology. The clk
api itself defines several driver-facing functions which operate on
struct clk. That api is documented in include/linux/clk.h.

Platforms and devices utilizing the common struct clk use the struct
clk_ops pointer in struct clk to perform the hardware-specific parts of
the operations defined in 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:

struct clk_ops {
int (*prepare)(struct clk_hw *hw);
void (*unprepare)(struct clk_hw *hw);
int (*is_prepared)(struct clk_hw *hw);
void (*unprepare_unused)(struct clk_hw *hw);
int (*enable)(struct clk_hw *hw);
void (*disable)(struct clk_hw *hw);
int (*is_enabled)(struct clk_hw *hw);
void (*disable_unused)(struct clk_hw *hw);
unsigned long (*recalc_rate)(struct clk_hw *hw,
unsigned long parent_rate);
long (*round_rate)(struct clk_hw *hw,
Expand All @@ -84,14 +88,16 @@ the operations defined in clk.h:
u8 index);
unsigned long (*recalc_accuracy)(struct clk_hw *hw,
unsigned long parent_accuracy);
int (*get_phase)(struct clk_hw *hw);
int (*set_phase)(struct clk_hw *hw, int degrees);
void (*init)(struct clk_hw *hw);
int (*debug_init)(struct clk_hw *hw,
struct dentry *dentry);
};

Part 3 - hardware clk implementations

The strength of the common struct clk comes from its .ops and .hw pointers
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:
Expand All @@ -107,7 +113,7 @@ struct clk_gate contains struct clk_hw hw as well as hardware-specific
knowledge about which register and bit controls this clk's gating.
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.
framework code and struct clk_core.

Let's walk through enabling this clk from driver code:

Expand Down Expand Up @@ -139,22 +145,18 @@ static void clk_gate_set_bit(struct clk_gate *gate)

Note that to_clk_gate is defined as:

#define to_clk_gate(_hw) container_of(_hw, struct clk_gate, clk)
#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

When implementing support for a new type of clock it only necessary to
When implementing support for a new type of clock it is only necessary to
include the following header:

#include <linux/clk-provider.h>

include/linux/clk.h is included within that header and clk-private.h
must never be included from the code which implements the operations for
a clock. More on that below in Part 5.

To construct a clk hardware structure for your platform you must define
the following:

Expand Down

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