By: fulinux
E-mail: fulinux@sina.com
Blog: https://blog.csdn.net/fulinus
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1. 概述

很多设备里面系统时钟架构极其复杂，让学习Clock驱动的盆友头大。这里我参考S3C2440的clock驱动写了一个virtual clock，即虚拟时钟驱动，分别包含clock的provider和consumer。
因为本文驱动示例对环境没有要求，所以本文就是在Ubuntu环境下进行。

2. virtual clock设计

设计一个虚拟的时钟引脚环境，尽量包括晶振osc、锁相环mpll(main pll)，分频器divider, 选择器mux和开关gate。这里我们预设osc时钟频率为12MHz,
mpll为400MHz，分频器可以获得100MHz、133Mhz、66MHz、50M。他们的连接方式如下：

虚拟时钟框架就是这么简单。

3. 虚拟时钟驱动

下一步就是实现虚拟时钟驱动程序，时钟驱动程序分为provider和consumer。以下分别介绍

3.1. provider驱动

provider驱动我们使用platform驱动框架，因此可以分两部分，一个是platform device部分，另一个是platform driver部分；

3.1.1. provider platform device部分

这一部分的代码较为简单如下所示：

//device/vir_clk_device.c 
#include <linux/init.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include "vir_clk_device.h"static struct vir_clk_platform_data vir_clk_info = {.data = 0,.index = 2333,
};static void vir_clk_release(struct device *dev)
{
}static struct platform_device vir_clk_device = {.name = "vir_clk",.id = -1,.dev = {.platform_data = &vir_clk_info,.release = vir_clk_release,}
};static int __init vir_clk_dev_init(void)
{int ret = 0;printk("[%s:%d]\\n", __func__, __LINE__);ret = platform_device_register(&vir_clk_device);return ret;
}static void __exit vir_clk_dev_exit(void)
{printk("[%s:%d]\\n", __func__, __LINE__);platform_device_unregister(&vir_clk_device);
}module_init(vir_clk_dev_init);
module_exit(vir_clk_dev_exit);
MODULE_DESCRIPTION("virtual clk platform device");
MODULE_LICENSE("GPL");

同时包含一个头文件：

//device/vir_clk_device.h 
#ifndef __VIR_CLK_DEVICE_H__
#define __VIR_CLK_DEVICE_H__struct vir_clk_platform_data {int data;int index;
};
#endif

它的Makefile文件如下：

OBJ_NAME := vir_clk_device
TARGET := $(OBJ_NAME).ko
obj-m := $(OBJ_NAME).o
PWD := $(shell pwd)KERNEL_SOURCE=/lib/modules/$(shell uname -r)/build
#KBUILD_EXTRA_SYMBOLS := $(KDIR)Module.symvers
all:$(MAKE) -C $(KERNEL_SOURCE) M=$(PWD) modulesclean:rm -rf .*.cmd *.o *.mod.c *.ko .tmp_versions *.order *symvers *Module.markers.PHONY: all clean install

为了方便查看内核信息，我们先讲dmesg信息清空：

sudo dmesg -c

编译和安装驱动：

$ sudo insmod vir_clk_device.ko 

查看下对应的运行信息：

$ dmesg 
[  723.980546] vir_clk_device: loading out-of-tree module taints kernel.
[  723.980574] vir_clk_device: module verification failed: signature and/or required key missing - tainting kernel
[  723.981650] [vir_clk_dev_init:27]

3.1.2. provider platform driver部分

//driver/vir_clk_driver.c 
#include <linux/module.h>
#include <linux/init.h>
#include <linux/platform_device.h>
#include <linux/clk-provider.h>
#include <linux/clkdev.h>#include "../device/vir_clk_device.h"static const char *osc_name[] = {"osc"};
static const char *mpll_p[] = {"div_mpll_4", "div_mpll_3"};
static const char *mpll_name[] = {"mpll"};
static const char *hclk_name[] = {"hclk"};
static unsigned int muxreg = 0;
static void __iomem *muxconf = &muxreg;
static unsigned int divreg = 0;
static void __iomem *divconf = &divreg;
static DEFINE_SPINLOCK(vir_clk_lock);struct virtual_clock {unsigned int endisable;struct clk_hw hw;
};#define to_virtual_clock(_hw) container_of(_hw, struct virtual_clock, hw)static int vir_clk_register_osc(struct platform_device *pdev)
{int ret = 0;struct clk *clk;clk = clk_register_fixed_rate(&pdev->dev, "osc", NULL, 0, 12000000);if (IS_ERR(clk)) {printk("[%s:%d] failed to register osc clock %ld\\n", __func__, __LINE__, PTR_ERR(clk));return -1;}ret = clk_register_clkdev(clk, "alias_osc", "osc");if (ret)printk("[%s:%d] failed to register clock lookup for osc\\n", __func__, __LINE__);return ret;
}static unsigned long mpll_recalc_rate(struct clk_hw *hw, unsigned long parent_rate)
{printk("[%s:%d] parent_rate = %ld\\n", __func__, __LINE__, parent_rate);return 400000000;//400M
}static int mpll_enable(struct clk_hw *hw)
{printk("[%s:%d] enable\\n", __func__, __LINE__);return 0;
}static void mpll_disable(struct clk_hw *hw)
{printk("[%s:%d] enable\\n", __func__, __LINE__);
}static long mpll_round_rate(struct clk_hw *hw,unsigned long drate, unsigned long *prate)
{printk("[%s:%d] drate = %ld\\n", __func__, __LINE__, drate);return drate;
}static int mpll_set_rate(struct clk_hw *hw,unsigned long drate, unsigned long prate)
{printk("[%s:%d] drate = %ld, prate = %ld\\n", __func__, __LINE__, drate, prate);return 0;
}static const struct clk_ops mpll_clk_ops = {.recalc_rate = mpll_recalc_rate,.enable     = mpll_enable,.disable    = mpll_disable,.round_rate = mpll_round_rate,.set_rate   = mpll_set_rate,
};static int vir_clk_register_pll(struct platform_device *pdev)
{int ret = 0;struct clk *clk;struct clk_hw hw;struct clk_init_data init;init.name = mpll_name[0];init.flags = CLK_GET_RATE_NOCACHE;init.parent_names = osc_name;init.num_parents = 1;init.ops = &mpll_clk_ops;hw.init = &init;clk = clk_register(&pdev->dev, &hw);if (IS_ERR(clk)) {printk("[%s:%d] mpll: failed to register pll clock %ld\\n", __func__, __LINE__, PTR_ERR(clk));return -1;}ret = clk_register_clkdev(clk, "fclk", "mpll");if (ret) {printk("[%s:%d] mpll: failed to register lookup for %d\\n", __func__, __LINE__, ret);return ret;}return 0;
}static struct clk_div_table div_mpll_4_d[] = {{ .val = 0, .div = 4},{ .val = 1, .div = 8},{/* sentinel */ },
};static struct clk_div_table div_mpll_3_d[] = {{ .val = 0, .div = 3},{ .val = 1, .div = 6},{/* sentinel */ },
};static int vir_clk_register_div(struct platform_device *pdev)
{int ret;struct clk *clk;clk = clk_register_divider_table(&pdev->dev,"div_mpll_4", "mpll", 0, divconf, 0, 1, 0, div_mpll_4_d, &vir_clk_lock);if (IS_ERR(clk)) {printk("[%s:%d] failed to register divides clock %ld\\n", __func__, __LINE__, PTR_ERR(clk));return -1;}ret = clk_register_clkdev(clk, "div_mpll_4", "div_mpll_4");if (ret) {printk("[%s:%d] mpll: failed to register lookup for %d\\n", __func__, __LINE__, ret);return ret;}clk = clk_register_divider_table(&pdev->dev,"div_mpll_3", "mpll", 0, divconf, 0, 1, 0, div_mpll_3_d, &vir_clk_lock);if (IS_ERR(clk)) {printk("[%s:%d] failed to register divides clock %ld\\n", __func__, __LINE__, PTR_ERR(clk));return -1;}ret = clk_register_clkdev(clk, "div_mpll_4", "div_mpll_3");if (ret) {printk("[%s:%d] mpll: failed to register lookup for %d\\n", __func__, __LINE__, ret);return ret;}return 0;
}static int vir_clk_register_muxes(struct platform_device *pdev)
{int ret;struct clk *clk;clk = clk_register_mux(&pdev->dev, hclk_name[0], mpll_p, 2, 0, muxconf, 1, 2, 0, &vir_clk_lock);if (IS_ERR(clk)) {printk("[%s:%d] failed to register mux clock %ld\\n", __func__, __LINE__, PTR_ERR(clk));return -1;}ret = clk_register_clkdev(clk, "alias_muxclk", "muxclk");if (ret) {printk("[%s:%d] mpll: failed to register lookup for %d\\n", __func__, __LINE__, ret);return ret;}return 0;
}static int virtual_clock_enable(struct clk_hw *hw)
{struct virtual_clock *virtual_clock_ptr = to_virtual_clock(hw);virtual_clock_ptr->endisable = 1;printk("%s %d gate enable\\n", __func__, __LINE__);return 0;
}static void virtual_clock_disable(struct clk_hw *hw)
{struct virtual_clock *virtual_clock_ptr = to_virtual_clock(hw);virtual_clock_ptr->endisable = 0;printk("%s %d gate disable\\n", __func__, __LINE__);
}static int virtual_clock_is_enabled(struct clk_hw *hw)
{struct virtual_clock *virtual_clock_ptr = to_virtual_clock(hw);printk("%s %d gate endisable = %d\\n", __func__, __LINE__, virtual_clock_ptr->endisable);return virtual_clock_ptr->endisable;
}static struct clk_ops virtual_clock_ops = {.enable = virtual_clock_enable,.disable = virtual_clock_disable,.is_enabled = virtual_clock_is_enabled,
};static int vir_clk_register_gate(struct platform_device *pdev)
{int ret = 0;struct virtual_clock *clk_gate_ptr = NULL;struct clk_init_data init_data;int gate_flag = 0;struct clk *clk;struct vir_clk_platform_data *pdata = (struct vir_clk_platform_data *)(pdev->dev.platform_data);clk_gate_ptr = devm_kzalloc(&pdev->dev, sizeof(struct virtual_clock), GFP_KERNEL);if (!clk_gate_ptr)return -ENOMEM;printk("%s %d\\n", __func__, __LINE__);memset(&init_data, 0, sizeof(init_data));init_data.parent_names = hclk_name;init_data.num_parents = 1;init_data.ops = &virtual_clock_ops;init_data.name = pdev->name;//init_data_flags = CLK_IS_ROOT;if (pdata != NULL) {clk_gate_ptr->endisable = 0;clk_gate_ptr->hw.init = &init_data;printk("%s %d\\n", __func__, __LINE__);if (pdata->data)gate_flag = 1;elsegate_flag = 2;printk("%s %d gate_flag = %d\\n", __func__, __LINE__, gate_flag);}printk("%s %d gate index = %d\\n", __func__, __LINE__, pdata->index);clk = devm_clk_register(&pdev->dev, &clk_gate_ptr->hw);if (IS_ERR(clk))return -EINVAL;printk("%s %d\\n", __func__, __LINE__);if (pdev->dev.of_node != NULL)ret = of_clk_add_provider(pdev->dev.of_node, of_clk_src_simple_get, clk);elseret = clk_register_clkdev(clk, "vir_clock", NULL);return ret;}static int vir_clk_probe(struct platform_device *pdev)
{int ret;ret = vir_clk_register_osc(pdev);printk("[%s:%d] ret = %d\\n", __func__, __LINE__, ret);ret = vir_clk_register_pll(pdev);printk("[%s:%d] ret = %d\\n", __func__, __LINE__, ret);ret = vir_clk_register_div(pdev);printk("[%s:%d] ret = %d\\n", __func__, __LINE__, ret);ret = vir_clk_register_muxes(pdev);printk("[%s:%d] ret = %d\\n", __func__, __LINE__, ret);ret = vir_clk_register_gate(pdev);printk("[%s:%d] ret=%d\\n", __func__, __LINE__, ret);return 0;
}static int vir_clk_remove(struct platform_device *pdev)
{printk("%s %d\\n", __func__, __LINE__);return 0;
}#ifdef CONFIG_OF
static const struct of_device_id of_vir_clk_match[] = {{ .compatible = "vir_clk", },{},
};
#endifstatic struct platform_driver vir_clk_driver = {.probe      = vir_clk_probe,.remove     = vir_clk_remove,.driver     = {.name   = "vir_clk",.owner  = THIS_MODULE,.of_match_table = of_match_ptr(of_vir_clk_match),},
};module_platform_driver(vir_clk_driver);MODULE_AUTHOR("fulinux");
MODULE_DESCRIPTION("virtual clk driver");
MODULE_LICENSE("GPL");

对应的Makefile文件：

OBJ_NAME := vir_clk_driver
TARGET := $(OBJ_NAME).ko
obj-m := $(OBJ_NAME).o
PWD := $(shell pwd)KERNEL_SOURCE=/lib/modules/$(shell uname -r)/build
#KBUILD_EXTRA_SYMBOLS := $(KDIR)Module.symvers
all:$(MAKE) -C $(KERNEL_SOURCE) M=$(PWD) modulesclean:rm -rf .*.cmd *.o *.mod.c *.ko .tmp_versions *.order *symvers *Module.markers.PHONY: all clean install

编译和安装驱动：

$ sudo insmod vir_clk_driver.ko 

查看内核打印信息：

[ 1009.333889] [vir_clk_probe:280] ret = 0
[ 1009.333891] [mpll_recalc_rate:59] parent_rate = 12000000
[ 1009.333895] [vir_clk_probe:283] ret = 0
[ 1009.333904] [vir_clk_probe:286] ret = 0
[ 1009.333909] [vir_clk_probe:290] ret = 0
[ 1009.333909] vir_clk_register_gate 237
[ 1009.333910] vir_clk_register_gate 250
[ 1009.333910] vir_clk_register_gate 255 gate_flag = 2
[ 1009.333910] vir_clk_register_gate 258 gate index = 2333
[ 1009.333914] vir_clk_register_gate 264
[ 1009.333914] [vir_clk_probe:293] ret=0

此时可以看到时钟的总览信息：

3.2. consumer驱动

consumer驱动我们使用platform驱动框架，因此也可以分两部分，一个是platform device部分，另一个是platform driver部分；

3.2.1. consumer platform device驱动

platform device源文件如下：

//device/vir_consumer_device.c 
#include <linux/init.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include "vir_consumer_device.h"static struct vir_clk_consumer_data data_info = {.con_id = "vir_clock",
};static void vir_clk_gate_consumer_release(struct device *dev)
{
}static struct platform_device vir_clk_gate_consumer_device = {.name = "vir_clk_consumer",.id = -1,.dev = {.platform_data = &data_info,.release = vir_clk_gate_consumer_release,}
};static int __init vir_clk_gate_consumer_init(void)
{int ret = 0;printk("%s:%d\\n\\n", __func__, __LINE__);ret = platform_device_register(&vir_clk_gate_consumer_device);return ret;
}static void __exit vir_clk_gate_consumer_exit(void)
{printk("%s:%d\\n\\n", __func__, __LINE__);platform_device_unregister(&vir_clk_gate_consumer_device);
}module_init(vir_clk_gate_consumer_init);
module_exit(vir_clk_gate_consumer_exit);
MODULE_DESCRIPTION("virtual clk gate platform device");
MODULE_LICENSE("GPL");
MODULE_AUTHOR("fulinux");

还有一个头文件：

//device/vir_consumer_device.h 
#ifndef __VIR_CONSUMER_DEVICE_H__
#define __VIR_CONSUMER_DEVICE_H__struct vir_clk_consumer_data {const char *con_id;
};#endif

对应的Makefile文件：

OBJ_NAME := vir_consumer_device
TARGET := $(OBJ_NAME).ko
obj-m := $(OBJ_NAME).o
PWD := $(shell pwd)KERNEL_SOURCE=/lib/modules/$(shell uname -r)/build
#KBUILD_EXTRA_SYMBOLS := $(KDIR)Module.symvers
all:$(MAKE) -C $(KERNEL_SOURCE) M=$(PWD) modulesclean:rm -rf .*.cmd *.o *.mod.c *.ko .tmp_versions *.order *symvers *Module.markers.PHONY: all clean install

3.2.2. consumer platform driver驱动

platform driver源文件如下：

//driver/vir_consumer_driver.c 
#include <linux/init.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/clk-provider.h>
#include <linux/clkdev.h>
#include <linux/clk.h>
#include "../device/vir_consumer_device.h"struct vir_clk_consumer {struct clk *clk;
};static int vir_clk_consumer_probe(struct platform_device *pdev)
{struct vir_clk_consumer_data *pdata = (struct vir_clk_consumer_data *)(pdev->dev.platform_data);struct vir_clk_consumer *consumer_ptr = NULL;printk("[%s:%d]\\n", __func__, __LINE__);consumer_ptr = devm_kzalloc(&pdev->dev, sizeof(struct vir_clk_consumer), GFP_KERNEL);if (!consumer_ptr)return -ENOMEM;printk("[%s:%d] clk_get 1\\n", __func__, __LINE__);consumer_ptr->clk = clk_get(&pdev->dev, pdata->con_id);printk("[%s:%d] clk_get 2\\n", __func__, __LINE__);if (IS_ERR(consumer_ptr->clk)) {printk("[%s:%d]\\n", __func__, __LINE__);return PTR_ERR(consumer_ptr->clk);}platform_set_drvdata(pdev, consumer_ptr);printk("[%s:%d] clk_prepare_enable 1\\n", __func__, __LINE__);clk_prepare_enable(consumer_ptr->clk);printk("[%s:%d] clk_prepare_enable 2\\n", __func__, __LINE__);return 0;
}static int vir_clk_consumer_remove(struct platform_device *pdev)
{struct vir_clk_consumer *consumer_ptr = platform_get_drvdata(pdev);printk("[%s:%d] clk_disable_unprepare 1\\n", __func__, __LINE__);clk_disable_unprepare(consumer_ptr->clk);printk("[%s:%d] clk_disable_unprepare 2\\n", __func__, __LINE__);printk("[%s:%d] clk_put 1\\n", __func__, __LINE__);clk_put(consumer_ptr->clk);printk("[%s:%d] clk_put 2\\n", __func__, __LINE__);return 0;
}#ifdef CONFIG_OF
static const struct of_device_id of_vir_clk_consumer_match[] = {{ .compatible = "vir_clk_consumer"},{},
};
#endifstatic struct platform_driver vir_clk_gate_driver = {.probe      = vir_clk_consumer_probe,.remove     = vir_clk_consumer_remove,.driver     = {.name   = "vir_clk_consumer",.owner  = THIS_MODULE,.of_match_table = of_match_ptr(of_vir_clk_consumer_match),},
};module_platform_driver(vir_clk_gate_driver);MODULE_DESCRIPTION("virtual clk gate platform driver");
MODULE_LICENSE("GPL");
MODULE_AUTHOR("fulinux");

编译后安装：

sudo insmod vir_consumer_driver.ko 

查看内核dmesg信息：

[ 5653.909066] [vir_clk_consumer_probe:18]
[ 5653.909067] [vir_clk_consumer_probe:24] clk_get 1
[ 5653.909068] [vir_clk_consumer_probe:26] clk_get 2
[ 5653.909069] [vir_clk_consumer_probe:33] clk_prepare_enable 1
[ 5653.909071] [mpll_enable:66] enable
[ 5653.909071] [virtual_clock_enable:199] gate enable
[ 5653.909072] [vir_clk_consumer_probe:35] clk_prepare_enable 2

同时我们查看下clock的总览信息：

可以看到这里除了div_mpll3没有被使用之外，其他几个都被prepare和enable了。而且也能够看到频率的依赖关系。

4. 结束语

最终的文件和目录结构：

需要注意：
因为clock provider驱动框架没有提供释放的api接口函数，所以这里如果驱动出现异常或者修改，都需要重启系统方可释放时钟资源。

参考：https://jerry-cheng.blog.csdn.net/article/details/107804007