分析用的内核版本为5.1.3
1.MFD全称
Multi-function Device,多功能设备
2. 为何会出现MFD子系统
由于出现了一类具有多种功能的外围设备或cpu内部集成的硬件模块
3. 有哪些多功能设备呢?
3.1 PMIC,电源管理芯片
da9063: 调节器,led控制器,看门狗,实时时钟控制器,温度传感器,震动马达驱动,长按关机功能(ON key)
max77843: 调节器,充电器,燃油量表,触觉反馈,led控制器,micro USB接口控制器
wm831x: 调节器,时钟,实时时钟控制器,看门狗,触摸控制器,温度传感器,背光控制器,状态led控制器,GPIO,长按关机功能(ON key),ADC
其它: 甚至具有codec功能
3.2 atmel-hlcdc: 显示控制器和背光pwm
3.3 Diolan DLN2: USB转I2C,SPI和GPIO控制器
3.4 Realtek PCI-E读卡器: SD/MMC和记忆棒读取器
4. MFD子系统解决的主要问题
在不同的内核子系统中注册这些驱动。特别是外部外围设备仅仅由一个结构体struct device(或是指定的i2c_client或spi_device)呈现
5. MFD子系统的优点有哪些?
5.1 允许在多个子系统中注册相同的设备
5.2 MFD驱动必须能否复用总线(主要是关于锁的处理)和处理中断请求
5.3 处理时钟
5.4 需要配置IP
5.5 允许驱动重用,多个多功能设备能重用其它子系统中的驱动
6. MFD提供的API
int mfd_add_devices(struct device *parent,int id, const struct mfd_cell *cells, int n_devs,
struct resource *mem_base, int irq_base, struct irq_domain *irq_domain);
extern void mfd_remove_devices(struct device *parent);
这些接口定义在include/linux/mfd/core.h中,在drivers/mfd/mtd-core.c中被实现
7. MFD提供的结构体
struct mfd_cell { const char *name; int id; /* refcounting for multiple drivers to use a single cell */ atomic_t *usage_count; int (*enable)(struct platform_device *dev); int (*disable)(struct platform_device *dev); int (*suspend)(struct platform_device *dev); int (*resume)(struct platform_device *dev); /* platform data passed to the sub devices drivers */ void *platform_data; size_t pdata_size; /* device properties passed to the sub devices drivers */ struct property_entry *properties; /* * Device Tree compatible string * See: Documentation/devicetree/usage-model.txt Chapter 2.2 for details */ const char *of_compatible; /* Matches ACPI */ const struct mfd_cell_acpi_match *acpi_match; /* * These resources can be specified relative to the parent device. * For accessing hardware you should use resources from the platform dev */ int num_resources; const struct resource *resources; /* don't check for resource conflicts */ bool ignore_resource_conflicts; /* * Disable runtime PM callbacks for this subdevice - see * pm_runtime_no_callbacks(). */ bool pm_runtime_no_callbacks; /* A list of regulator supplies that should be mapped to the MFD * device rather than the child device when requested */ const char * const *parent_supplies; int num_parent_supplies; };
8. 示例分析
8.1 分析tps6507x的多功能驱动
8.1.1 涉及的文件
drivers/mfd/tps6507x.c
include/linux/mfd/tps6507x.h
drivers/regulator/tps6507x-regulator.c
drivers/input/touchscreen/tps6507x-ts.c
8.1.2 涉及的结构体
static const struct mfd_cell tps6507x_devs[] = { { .name = "tps6507x-pmic", }, { .name = "tps6507x-ts", }, };
从以上结构体可以得出,tps6507x系列芯片提供两种功能: 电源管理功能(regulator)+触摸屏功能(touchscreen)
static struct i2c_driver tps6507x_i2c_driver = { .driver = { .name = "tps6507x", .of_match_table = of_match_ptr(tps6507x_of_match), }, .probe = tps6507x_i2c_probe, .id_table = tps6507x_i2c_id, };
这个结构体为tps6507x提供探测函数tps6507x_i2c_probe
struct tps6507x_dev { struct device *dev; struct i2c_client *i2c_client; int (*read_dev)(struct tps6507x_dev *tps6507x, char reg, int size, void *dest); int (*write_dev)(struct tps6507x_dev *tps6507x, char reg, int size, void *src); /* Client devices */ struct tps6507x_pmic *pmic; };
tps6507x 的读写接口就是放在这个结构体中,这也就是所谓的共性
8.1.3 对tps6507x进行初始化
subsys_initcall(tps6507x_i2c_init);
调用路径如下:
tps6507x_i2c_init->i2c_add_driver
8.1.4 探测函数tps6507x_i2c_probe做了些什么？
注册tps6507x的读写函数: tps6507x_i2c_read_device和tps6507x_i2c_write_device到结构体struct tps6507x_dev中
8.1.5 tps6507x的两种功能实现在哪里呢?
drivers/regulator/tps6507x-regulator.c,这里面实现电源管理功能（电压调节器驱动）
drivers/input/touchscreen/tps6507x-ts.c,这里面实现触摸屏功能
8.1.6 tps6507x电压调节器驱动
8.1.6.1 调用路径
subsys_initcall(tps6507x_pmic_init);
tps6507x_pmic_init->platform_driver_register
8.1.6.2 探测函数tps6507x_pmic_probe干了些什么?
获取共用的结构体struct tps6507x_dev
再注册相关的结构体以便提供pmic的相关操作接口,如下:
static struct regulator_ops tps6507x_pmic_ops = { .is_enabled = tps6507x_pmic_is_enabled, 检查tps6507x的pmic功能是否已经使能了 .enable = tps6507x_pmic_enable, 使能tps6507x的pmic功能 .disable = tps6507x_pmic_disable, 禁用tsp6507x的pmic功能 .get_voltage_sel = tps6507x_pmic_get_voltage_sel, 获取电压值 .set_voltage_sel = tps6507x_pmic_set_voltage_sel, 设置电压值 .list_voltage = regulator_list_voltage_table, 列出电压表 .map_voltage = regulator_map_voltage_ascend, };
8.1.7 tps6507x触摸屏驱动
8.1.7.1 驱动在哪里?
drivers/input/touchscreen/tps6507x-ts.c
8.1.7.2 分析probe函数都做了些什么?
获取公用的结构体struct tps6507x_dev
填充结构体struct tps6507x_ts，关键是注册了函数tps6507x_ts_poll
参考资料: