介绍Clock的功能和使用方法。
模块介绍
Clock是时钟模块的控制器。
功能介绍
Linux为了做好时钟管理，提供了一个时钟管理框架Common Clock Framework（以下简称CCF），为设备驱动提供统一的操作接口，使设备驱动不必关心时钟硬件实现的具体细节。
其结构包括以下几个部分：
clock provider：对应上图的右侧部分，即clock controller，负责提供系统所需的各种时钟。
clock consumer：对应上图的左侧部分，即使用时钟的一些设备驱动。
clock framework：CCF的核心部分，向clock consumers提供操作clock的通用API；实现时钟管理的核心逻辑，将与硬件相关的clock控制逻辑封装成操作函数集，交由clock provider实现。
device tree：CCF允许在设备树中声明可用的时钟与设备的关联。
Clock系统相关的器件包括：
- 用于产生clock的Oscillator（有源振荡器，也称作谐振荡器）或者Crystal（无源振荡器，也称晶振）
- 用于倍频的PLL（锁相环，Phase Locked Loop）
- 用于分频的Divider
- 用于时钟源选择的Mux
- 用于时钟开关控制的Gate
系统中可能存在很多个这样的硬件模块，呈树形结构，linux将他们管理成一个时钟树（clock-tree），根节点一般是晶振，接着是pll，然后是mux或者div，最终叶子节点一般是gate。CCF实现了多种基础时钟类型，例如固定速率时钟fixed_rate clock、门控时钟gate clock、分频器时钟divider clock和复用器时钟mux clock等。一般为了方便使用，会根据时钟树设计，实现一些时钟类型。
源码结构介绍
Clock控制器驱动代码在drivers/clk/spacemit目录下：
drivers/clk/spacemit
|-- ccu_ddn.c #ddn时钟类型源码
|-- ccu_ddn.h
|-- ccu_ddr.c #ddr时钟类型源码
|-- ccu_ddr.h
|-- ccu_dpll.c #dpll时钟类型源码
|-- ccu_dpll.h
|-- ccu_mix.c #mix时钟类型源码
|-- ccu_mix.h
|-- ccu_pll.c #pll时钟类型源码
|-- ccu_pll.h
|-- ccu-spacemit-k1x.c #k1 clock controller驱动
|-- ccu-spacemit-k1x.h
|-- Kconfig
|-- Makefile
clock控制器驱动实现了5种时钟类型:
- pll类型，锁相环类型
- dpll类型，ddr相关的锁相环类型
- ddn类型，分数divider，有一级除频，对应分母，一级倍频，对应分子
- mix类型，混合类型，支持gate/mux/divider的任一种或者随意组合
- ddr类型，ddr相关的特殊时钟类型
配置介绍
主要包括驱动使能配置和dts配置
CONFIG配置
CONFIG_COMMON_CLK为Common Clock Framework提供支持，默认情况下，此选项为Y
Device Drivers
Common Clock Framework (COMMON_CLK[=y])
CONFIG_SPACEMIT_K1X_CCU 为K1 Clock控制器驱动提供支持，默认情况下，此选型为Y
Device Drivers
Common Clock Framework (COMMON_CLK[=y])
Clock support for Spacemit k1x SoCs (SPACEMIT_K1X_CCU [=y])
DTS配置
clock controller的dts配置如下：
/ {
clocks {
#address-cells = <0x2>;
#size-cells = <0x2>;
ranges;
vctcxo_24: clock-vctcxo_24 {
#clock-cells = <0>;
compatible = "fixed-clock";
clock-frequency = <24000000>;
clock-output-names = "vctcxo_24";
};
vctcxo_3: clock-vctcxo_3 {
#clock-cells = <0>;
compatible = "fixed-clock";
clock-frequency = <3000000>;
clock-output-names = "vctcxo_3";
};
vctcxo_1: clock-vctcxo_1 {
#clock-cells = <0>;
compatible = "fixed-clock";
clock-frequency = <1000000>;
clock-output-names = "vctcxo_1";
};
pll1_2457p6_vco: clock-pll1_2457p6_vco {
#clock-cells = <0>;
compatible = "fixed-clock";
clock-frequency = <2457600000>;
clock-output-names = "pll1_2457p6_vco";
};
clk_32k: clock-clk32k {
#clock-cells = <0>;
compatible = "fixed-clock";
clock-frequency = <32000>;
clock-output-names = "clk_32k";
};
pll_clk_cluster0: clock-pll_clk_cluster0 {
#clock-cells = <0>;
compatible = "fixed-clock";
clock-frequency = <10000000>;
clock-output-names = "pll_clk_cluster0";
};
pll_clk_cluster1: clock-pll_clk_cluster1 {
#clock-cells = <0>;
compatible = "fixed-clock";
clock-frequency = <10000000>;
clock-output-names = "pll_clk_cluster1";
};
};
soc: soc {
...
ccu: clock-controller@d4050000 {
compatible = "spacemit,k1x-clock";
reg = <0x0 0xd4050000 0x0 0x209c>,
<0x0 0xd4282800 0x0 0x400>,
<0x0 0xd4015000 0x0 0x1000>,
<0x0 0xd4090000 0x0 0x1000>,
<0x0 0xd4282c00 0x0 0x400>,
<0x0 0xd8440000 0x0 0x98>,
<0x0 0xc0000000 0x0 0x4280>,
<0x0 0xf0610000 0x0 0x20>,
<0x0 0xc0880000 0x0 0x2050>,
<0x0 0xc0888000 0x0 0x30>;
reg-names = "mpmu", "apmu", "apbc", "apbs", "ciu", "dciu", "ddrc", "apbc2", "rcpu", "rcpu2";
clocks = <&vctcxo_24>, <&vctcxo_3>, <&vctcxo_1>, <&pll1_2457p6_vco>,
<&clk_32k>;
clock-names = "vctcxo_24", "vctcxo_3", "vctcxo_1", "pll1_2457p6_vco",
"clk_32k";
#clock-cells = <1>;
status = "okay";
};
...
};
};
模块如要使用clock功能，需要在dts配置clocks和clock-names属性，然后在驱动中通过CCF API进行Clock相关的操作。以can为例：
flexcan0: fdcan@d4028000 {
compatible = "spacemit,k1x-flexcan";
reg = <0x0 0xd4028000 0x0 0x4000>;
interrupts = <16>;
interrupt-parent = <&intc>;
clocks = <&ccu CLK_CAN0>,<&ccu CLK_CAN0_BUS>; #配置模块需要使用的时钟index
clock-names = "per","ipg"; #配置clocks对应的名称，驱动里可以通过这个字符串获取对应时钟
resets = <&reset RESET_CAN0>;
fsl,clk-source = <0>;
status = "disabled";
};
接口描述
API介绍
CCF为设备驱动提供了通用的时钟操作的接口
- get接口
/*
* clk_get - get clk
* @dev: device
* @id: clock name of dts "clock-names"
*/
struct clk *clk_get(struct device *dev, const char *id);
/*
* clk_get - get clk
* @dev: device
* @id: clock name of dts "clock-names"
*/
struct clk *clk_get(struct device *dev, const char *id);
/*
* devm_clk_get - get clk
* @dev：device
* @id：clock name of dts "clock-names"
*/
struct clk *devm_clk_get(struct device *dev, const char *id);
/*
* of_clk_get_by_name - get clk by name
* @np：device_node
* @id：clock name of dts "clock-names"
*/
struct clk *of_clk_get_by_name(struct device_node *np, const char *name);
上述接口，第二个参数如果缺省，会默认获取dts里"clocks"项配置的第一个时钟。
- put接口
/*
* clk_put - put clk
* @dev: device
* @id: clock name of dts "clock-names"
*/
void clk_put(struct clk *clk);
/*
* devm_clk_put - put clk
* @dev: device
* @id: clock name of dts "clock-names"
*/
void devm_clk_put(struct device *dev, struct clk *clk);
- prepare
/**
* clk_prepare - prepare a clock source
* @clk: clock source
* This prepares the clock source for use.
* Must not be called from within atomic context.
*/
int clk_prepare(struct clk *clk);
- unprepare
/**
* clk_unprepare - undo preparation of a clock source
* @clk: clock source
* This undoes a previously prepared clock. The caller must balance
* the number of prepare and unprepare calls.
* Must not be called from within atomic context.
*/
void clk_unprepare(struct clk *clk);
- enable
/**
* clk_enable - inform the system when the clock source should be running.
* @clk: clock source
* If the clock can not be enabled/disabled, this should return success.
* May be called from atomic contexts.
* Returns success (0) or negative errno.
*/
int clk_enable(struct clk *clk);
- disable
/**
* clk_disable - inform the system when the clock source is no longer required.
* @clk: clock source
* Inform the system that a clock source is no longer required by
* a driver and may be shut down.
* May be called from atomic contexts.
* Implementation detail: if the clock source is shared between
* multiple drivers, clk_enable() calls must be balanced by the
* same number of clk_disable() calls for the clock source to be
* disabled.
*/
void clk_disable(struct clk *clk);
clk_prepare_enable是clk_prepare和clk_enable的组合，clk_disable_unprepare是clk_unprepare和clk_disable的组合
- set rate
/**
* clk_set_rate - set the clock rate for a clock source
* @clk: clock source
* @rate: desired clock rate in Hz
* Updating the rate starts at the top-most affected clock and then
* walks the tree down to the bottom-most clock that needs updating.
* Returns success (0) or negative errno.
*/
int clk_set_rate(struct clk *clk, unsigned long rate);
- get rate
/**
* clk_get_rate - obtain the current clock rate (in Hz) for a clock source.
* This is only valid once the clock source has been enabled.
* @clk: clock source
*/
unsigned long clk_get_rate(struct clk *clk);
- set parent
/**
* clk_set_parent - set the parent clock source for this clock
* @clk: clock source
* @parent: parent clock source
* Returns success (0) or negative errno.
*/
int clk_set_parent(struct clk *clk, struct clk *parent);
- get parent
/**
* clk_get_parent - get the parent clock source for this clock
* @clk: clock source
* Returns struct clk corresponding to parent clock source, or
* valid IS_ERR() condition containing errno.
*/
struct clk *clk_get_parent(struct clk *clk);
- round rate
/**
* clk_round_rate - adjust a rate to the exact rate a clock can provide
* @clk: clock source
* @rate: desired clock rate in Hz
* This answers the question "if I were to pass @rate to clk_set_rate(),
* what clock rate would I end up with?" without changing the hardware
* in any way. In other words:
* rate = clk_round_rate(clk, r);
* and:
* clk_set_rate(clk, r);
* rate = clk_get_rate(clk);
* are equivalent except the former does not modify the clock hardware
* in any way.
* Returns rounded clock rate in Hz, or negative errno.
*/
long clk_round_rate(struct clk *clk, unsigned long rate);
Debug介绍
可以通过debugfs进行调试
- 打印时钟树
/sys/kernel/debug/clk/clk_summary常用于打印时钟树结构，查看各个时钟节点的状态，频率，父时钟等信息。
root# cat /sys/kernel/debug/clk/clk_summary
- 查看具体时钟节点
还可以单独查看具体时钟节点的状态，频率，父时钟等信息。以can0_clk为例：
root:/sys/kernel/debug/clk/can0_clk # ls -l
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_accuracy
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_duty_cycle
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_enable_count
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_flags
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_max_rate
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_min_rate
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_notifier_count
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_parent
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_phase
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_possible_parents
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_prepare_count
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_prepare_enable
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_protect_count
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_rate
root:/sys/kernel/debug/clk/can0_clk# cat clk_prepare_count #查看enable状态
0
root:/sys/kernel/debug/clk/can0_clk# cat clk_rate #查看当前频率
20000000
root:/sys/kernel/debug/clk/can0_clk# cat clk_parent #查看当前父时钟
pll3_20
root:/sys/kernel/debug/clk/can0_clk#
- 改变时钟配置
在driver/clk/clk.c中加上CLOCK_ALLOW_WRITE_DEBUGFS宏定义，就可以对debugfs下的一些clk节点进行写操作，否则只有读操作权限
/sys/kernel/debug/clk/can0_clk # ls -l
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_accuracy
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_duty_cycle
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_enable_count
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_flags
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_max_rate
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_min_rate
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_notifier_count
-rw-r--r-- 1 root root 0 Jan 1 08:03 clk_parent #可读可写
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_phase
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_possible_parents
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_prepare_count
-rw-r--r-- 1 root root 0 Jan 1 08:03 clk_prepare_enable #可读可写
-r--r--r-- 1 root root 0 Jan 1 08:03 clk_protect_count
-rw-r--r-- 1 root root 0 Jan 1 08:03 clk_rate #可读可写
/sys/kernel/debug/clk/can0_clk # cat clk_rate #查看频率
20000000
/sys/kernel/debug/clk/can0_clk # echo 40000000 > clk_rate #设置频率为40MHz
/sys/kernel/debug/clk/can0_clk # cat clk_rate #确认设置结果
40000000
/sys/kernel/debug/clk/can0_clk # cat clk_parent #查看父时钟
pll3_40
/sys/kernel/debug/clk/can0_clk # echo 0 > clk_parent #设置父时钟为index为0的时钟源
/sys/kernel/debug/clk/can0_clk # cat clk_parent #确认设置结果
pll3_20
/sys/kernel/debug/clk/can0_clk # cat clk_prepare_enable #查看prepare_enable状态
0
/sys/kernel/debug/clk/can0_clk # echo 1 > clk_prepare_enable #prepare并enable时钟节点
/sys/kernel/debug/clk/can0_clk # cat clk_prepare_enable #确认设置结果
1
/sys/kernel/debug/clk/can0_clk # echo 0 > clk_prepare_enable #unprepare并disable时钟节点
/sys/kernel/debug/clk/can0_clk # cat clk_prepare_enable #确认设置结果
0
/sys/kernel/debug/clk/can0_clk #