Linux 内核提供了一套可缓存的设备 IO 寄存器访问机制，即 regmap。regmap 机制支持以统一的接口，访问多种不同类型的设备 IO 寄存器，如内存映射的设备 IO 寄存器，和需要通过 I2C、I3C、SPI、AC97 和 SLIMBUS 等总线访问的设备寄存器等。内存映射设备 IO 寄存器和 I2C 总线是嵌入式系统中比较常见的控制设备的方式，regmap 机制对这些方式提供了良好的支持。
内存映射设备 IO 寄存器访问
内存映射设备 IO 寄存器的设备将设备的 IO 寄存器映射到物理内存地址空间，软件访问设备 IO 寄存器就像访问普通的物理内存一样。设备的 IO 寄存器在物理内存地址空间中的具体区域，由整个硬件系统的设计决定。
由于内存管理单元 MMU 及虚拟内存的应用，在 Linux 内核设备驱动程序中，也无法直接通过物理内存地址来访问设备的 IO 寄存器。在 Linux 内核设备驱动程序中，访问内存映射设备 IO 寄存器的方法如下：
- 在设备树文件的设备节点定义中说明内存映射设备 IO 寄存器在物理内存地址空间中的地址范围，这包括起始物理地址和地址空间大小，如 arch/arm64/boot/dts/rockchip/rk3399.dtsi 文件中 I2S0 设备节点的定义：
i2s0: i2s@ff880000 {
compatible = "rockchip,rk3399-i2s", "rockchip,rk3066-i2s";
reg = <0x0 0xff880000 0x0 0x1000>;
. . . . . .
};
reg = <0x0 0xff880000 0x0 0x1000>; 行说明了这个设备的内存映射设备 IO 寄存器在物理内存地址空间中的地址范围，起始地址为 0xff880000，地址空间大小为 0x1000，即 4KB。
- 创建寄存器映射配置，如 sound/soc/rockchip/rockchip_i2s.c 文件中的寄存器映射配置：
static bool rockchip_i2s_wr_reg(struct device *dev, unsigned int reg)
{
switch (reg) {
case I2S_TXCR:
case I2S_RXCR:
case I2S_CKR:
case I2S_DMACR:
case I2S_INTCR:
case I2S_XFER:
case I2S_CLR:
case I2S_TXDR:
return true;
default:
return false;
}
}
static bool rockchip_i2s_rd_reg(struct device *dev, unsigned int reg)
{
switch (reg) {
case I2S_TXCR:
case I2S_RXCR:
case I2S_CKR:
case I2S_DMACR:
case I2S_INTCR:
case I2S_XFER:
case I2S_CLR:
case I2S_TXDR:
case I2S_RXDR:
case I2S_FIFOLR:
case I2S_INTSR:
return true;
default:
return false;
}
}
static bool rockchip_i2s_volatile_reg(struct device *dev, unsigned int reg)
{
switch (reg) {
case I2S_INTSR:
case I2S_CLR:
case I2S_FIFOLR:
case I2S_TXDR:
case I2S_RXDR:
return true;
default:
return false;
}
}
static bool rockchip_i2s_precious_reg(struct device *dev, unsigned int reg)
{
switch (reg) {
case I2S_RXDR:
return true;
default:
return false;
}
}
static const struct reg_default rockchip_i2s_reg_defaults[] = {
{0x00, 0x0000000f},
{0x04, 0x0000000f},
{0x08, 0x00071f1f},
{0x10, 0x001f0000},
{0x14, 0x01f00000},
};
static const struct regmap_config rockchip_i2s_regmap_config = {
.reg_bits = 32,
.reg_stride = 4,
.val_bits = 32,
.max_register = I2S_RXDR,
.reg_defaults = rockchip_i2s_reg_defaults,
.num_reg_defaults = ARRAY_SIZE(rockchip_i2s_reg_defaults),
.writeable_reg = rockchip_i2s_wr_reg,
.readable_reg = rockchip_i2s_rd_reg,
.volatile_reg = rockchip_i2s_volatile_reg,
.precious_reg = rockchip_i2s_precious_reg,
.cache_type = REGCACHE_FLAT,
};
寄存器映射配置由 struct regmap_config 结构体来描述，它告诉 regmap 机制设备寄存器的位宽，设备寄存器的值的位宽，最大的设备寄存器，有特殊默认值的设备寄存器的默认值，设备寄存器的读写属性，及设备寄存器访问的缓存类型等。
Linux 设备驱动程序通过寄存器映射配置，为 regmap 机制提供缓存访问所需的信息。
可能有很多人觉得，由于设备 IO 寄存器的特殊性，对设备 IO 寄存器的访问都是不加缓存的。实际上，CPU 不缓存对设备 IO 寄存器的访问，但 Linux 内核的 regmap 机制，在内存中开辟了一块区域来做设备 IO 寄存器的缓存访问。
- 在设备驱动程序的
probe操作中，获得 IO 重映射资源，并初始化内存映射 IO，创建struct regmap结构对象，如 sound/soc/rockchip/rockchip_i2s.c 文件中的rockchip_i2s_probe()操作：
static int rockchip_i2s_probe(struct platform_device *pdev)
{
struct device_node *node = pdev->dev.of_node;
const struct of_device_id *of_id;
struct rk_i2s_dev *i2s;
struct snd_soc_dai_driver *soc_dai;
struct resource *res;
void __iomem *regs;
. . . . . .
regs = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
if (IS_ERR(regs)) {
ret = PTR_ERR(regs);
goto err_clk;
}
i2s->regmap = devm_regmap_init_mmio(&pdev->dev, regs,
&rockchip_i2s_regmap_config);
if (IS_ERR(i2s->regmap)) {
dev_err(&pdev->dev,
"Failed to initialise managed register map\n");
ret = PTR_ERR(i2s->regmap);
goto err_clk;
}
. . . . . .
return ret;
}
这里看到 devm_platform_get_and_ioremap_resource() 函数，获得在设备树文件中定义的 IO 重映射资源。它的返回值是类型为 void __iomem * 的内存映射设备 IO 寄存器地址空间基地址在内核内存地址空间的虚拟地址，并通过传出参数 struct resource 返回内存映射设备 IO 寄存器的物理地址空间。
通过 devm_platform_get_and_ioremap_resource() 函数返回的指针，Linux 设备驱动程序可以像访问普通内存一样访问设备 IO 寄存器，如：
u32 val;
. . . . . .
val = readl(regs + I2C_REG_STATUS);
. . . . . .
writel(regs + I2C_REG_CONFIGURE, 1);
regmap 机制可以提供的更多，如方便的读、写和更新操作函数，缓存的访问，及通过 debugfs 分析调试的能力等。调用 devm_regmap_init_mmio() 函数创建 struct regmap 是明智的。
- 通过 regmap 机制提供的读、写和更新等操作函数访问设备 IO 寄存器，如 sound/soc/rockchip/rockchip_i2s.c 文件中的如下代码片段：
if (!i2s->rx_start) {
regmap_update_bits(i2s->regmap, I2S_XFER,
I2S_XFER_TXS_START |
I2S_XFER_RXS_START,
I2S_XFER_TXS_STOP |
I2S_XFER_RXS_STOP);
udelay(150);
regmap_update_bits(i2s->regmap, I2S_CLR,
I2S_CLR_TXC | I2S_CLR_RXC,
I2S_CLR_TXC | I2S_CLR_RXC);
regmap_read(i2s->regmap, I2S_CLR, &val);
/* Should wait for clear operation to finish */
while (val) {
regmap_read(i2s->regmap, I2S_CLR, &val);
retry--;
if (!retry) {
dev_warn(i2s->dev, "fail to clear\n");
break;
}
}
}
可用以访问设备 IO 寄存器的函数有很多，如：
int regmap_write(struct regmap *map, unsigned int reg, unsigned int val);
int regmap_write_async(struct regmap *map, unsigned int reg, unsigned int val);
int regmap_raw_write(struct regmap *map, unsigned int reg,
const void *val, size_t val_len);
int regmap_read(struct regmap *map, unsigned int reg, unsigned int *val);
int regmap_raw_read(struct regmap *map, unsigned int reg,
void *val, size_t val_len);
int regmap_update_bits_base(struct regmap *map, unsigned int reg,
unsigned int mask, unsigned int val,
bool *change, bool async, bool force);
static inline int regmap_update_bits(struct regmap *map, unsigned int reg,
unsigned int mask, unsigned int val)
{
return regmap_update_bits_base(map, reg, mask, val, NULL, false, false);
}
static inline int regmap_set_bits(struct regmap *map,
unsigned int reg, unsigned int bits)
{
return regmap_update_bits_base(map, reg, bits, bits,
NULL, false, false);
}
static inline int regmap_clear_bits(struct regmap *map,
unsigned int reg, unsigned int bits)
{
return regmap_update_bits_base(map, reg, bits, 0, NULL, false, false);
}
int regmap_test_bits(struct regmap *map, unsigned int reg, unsigned int bits);
访问内存映射的设备 IO 寄存器是设备驱动程序所需的最基本的操作。
regmap 的实现
struct regmap_config 的定义 (位于 include/linux/regmap.h) 如下：
enum regcache_type {
REGCACHE_NONE,
REGCACHE_RBTREE,
REGCACHE_COMPRESSED,
REGCACHE_FLAT,
};
. . . . . .
struct reg_default {
unsigned int reg;
unsigned int def;
};
. . . . . .
struct regmap_range {
unsigned int range_min;
unsigned int range_max;
};
#define regmap_reg_range(low, high) { .range_min = low, .range_max = high, }
. . . . . .
struct regmap_access_table {
const struct regmap_range *yes_ranges;
unsigned int n_yes_ranges;
const struct regmap_range *no_ranges;
unsigned int n_no_ranges;
};
typedef void (*regmap_lock)(void *);
typedef void (*regmap_unlock)(void *);
. . . . . .
struct regmap_config {
const char *name;
int reg_bits;
int reg_stride;
int pad_bits;
int val_bits;
bool (*writeable_reg)(struct device *dev, unsigned int reg);
bool (*readable_reg)(struct device *dev, unsigned int reg);
bool (*volatile_reg)(struct device *dev, unsigned int reg);
bool (*precious_reg)(struct device *dev, unsigned int reg);
bool (*writeable_noinc_reg)(struct device *dev, unsigned int reg);
bool (*readable_noinc_reg)(struct device *dev, unsigned int reg);
bool disable_locking;
regmap_lock lock;
regmap_unlock unlock;
void *lock_arg;
int (*reg_read)(void *context, unsigned int reg, unsigned int *val);
int (*reg_write)(void *context, unsigned int reg, unsigned int val);
bool fast_io;
unsigned int max_register;
const struct regmap_access_table *wr_table;
const struct regmap_access_table *rd_table;
const struct regmap_access_table *volatile_table;
const struct regmap_access_table *precious_table;
const struct regmap_access_table *wr_noinc_table;
const struct regmap_access_table *rd_noinc_table;
const struct reg_default *reg_defaults;
unsigned int num_reg_defaults;
enum regcache_type cache_type;
const void *reg_defaults_raw;
unsigned int num_reg_defaults_raw;
unsigned long read_flag_mask;
unsigned long write_flag_mask;
bool zero_flag_mask;
bool use_single_read;
bool use_single_write;
bool can_multi_write;
enum regmap_endian reg_format_endian;
enum regmap_endian val_format_endian;
const struct regmap_range_cfg *ranges;
unsigned int num_ranges;
bool use_hwlock;
unsigned int hwlock_id;
unsigned int hwlock_mode;
bool can_sleep;
};
在 struct regmap_config 中，驱动程序除了可以用 writeable_reg 等回调函数来描述设备 IO 寄存器的读写属性外，还可以用 struct regmap_access_table 来描述。如果具有相同读写属性的设备 IO 寄存器是连续的，则 struct regmap_access_table 要方便很多，否则用回调函数比较方便。
Linux 设备驱动程序，可以通过 reg_read 和 reg_write 字段配置设备 IO 寄存器的读写操作。对于 I2C、SPI、I3C、AC97 和 mmio 等标准总线，Linux 内核已经提供相应的设备 IO 寄存器的读写操作。对于比较特别的设备，设备驱动程序可以自行提供读写操作。
设备驱动程序通过 devm_regmap_init_mmio() 创建并初始化 struct regmap，devm_regmap_init_mmio() 定义 (位于 include/linux/regmap.h) 如下：
struct regmap *__devm_regmap_init_mmio_clk(struct device *dev,
const char *clk_id,
void __iomem *regs,
const struct regmap_config *config,
struct lock_class_key *lock_key,
const char *lock_name);
. . . . . .
#ifdef CONFIG_LOCKDEP
#define __regmap_lockdep_wrapper(fn, name, ...) \
( \
({ \
static struct lock_class_key _key; \
fn(__VA_ARGS__, &_key, \
KBUILD_BASENAME ":" \
__stringify(__LINE__) ":" \
"(" name ")->lock"); \
}) \
)
#else
#define __regmap_lockdep_wrapper(fn, name, ...) fn(__VA_ARGS__, NULL, NULL)
#endif
. . . . . .
#define devm_regmap_init_mmio_clk(dev, clk_id, regs, config) \
__regmap_lockdep_wrapper(__devm_regmap_init_mmio_clk, #config, \
dev, clk_id, regs, config)
/**
* devm_regmap_init_mmio() - Initialise managed register map
*
* @dev: Device that will be interacted with
* @regs: Pointer to memory-mapped IO region
* @config: Configuration for register map
*
* The return value will be an ERR_PTR() on error or a valid pointer
* to a struct regmap. The regmap will be automatically freed by the
* device management code.
*/
#define devm_regmap_init_mmio(dev, regs, config) \
devm_regmap_init_mmio_clk(dev, NULL, regs, config)
创建并初始化 struct regmap 的工作由 __regmap_init_mmio_clk() 函数执行，这个函数定义 (位于 drivers/base/regmap/regmap-mmio.c) 如下：
struct regmap_mmio_context {
void __iomem *regs;
unsigned val_bytes;
bool attached_clk;
struct clk *clk;
void (*reg_write)(struct regmap_mmio_context *ctx,
unsigned int reg, unsigned int val);
unsigned int (*reg_read)(struct regmap_mmio_context *ctx,
unsigned int reg);
};
static int regmap_mmio_regbits_check(size_t reg_bits)
{
switch (reg_bits) {
case 8:
case 16:
case 32:
#ifdef CONFIG_64BIT
case 64:
#endif
return 0;
default:
return -EINVAL;
}
}
static int regmap_mmio_get_min_stride(size_t val_bits)
{
int min_stride;
switch (val_bits) {
case 8:
/* The core treats 0 as 1 */
min_stride = 0;
return 0;
case 16:
min_stride = 2;
break;
case 32:
min_stride = 4;
break;
#ifdef CONFIG_64BIT
case 64:
min_stride = 8;
break;
#endif
default:
return -EINVAL;
}
return min_stride;
}
. . . . . .
static void regmap_mmio_write32le(struct regmap_mmio_context *ctx,
unsigned int reg,
unsigned int val)
{
writel(val, ctx->regs + reg);
}
static void regmap_mmio_write32be(struct regmap_mmio_context *ctx,
unsigned int reg,
unsigned int val)
{
iowrite32be(val, ctx->regs + reg);
}
#ifdef CONFIG_64BIT
static void regmap_mmio_write64le(struct regmap_mmio_context *ctx,
unsigned int reg,
unsigned int val)
{
writeq(val, ctx->regs + reg);
}
#endif
. . . . . .
static unsigned int regmap_mmio_read32le(struct regmap_mmio_context *ctx,
unsigned int reg)
{
return readl(ctx->regs + reg);
}
static unsigned int regmap_mmio_read32be(struct regmap_mmio_context *ctx,
unsigned int reg)
{
return ioread32be(ctx->regs + reg);
}
#ifdef CONFIG_64BIT
static unsigned int regmap_mmio_read64le(struct regmap_mmio_context *ctx,
unsigned int reg)
{
return readq(ctx->regs + reg);
}
#endif
. . . . . .
static struct regmap_mmio_context *regmap_mmio_gen_context(struct device *dev,
const char *clk_id,
void __iomem *regs,
const struct regmap_config *config)
{
struct regmap_mmio_context *ctx;
int min_stride;
int ret;
ret = regmap_mmio_regbits_check(config->reg_bits);
if (ret)
return ERR_PTR(ret);
if (config->pad_bits)
return ERR_PTR(-EINVAL);
min_stride = regmap_mmio_get_min_stride(config->val_bits);
if (min_stride < 0)
return ERR_PTR(min_stride);
if (config->reg_stride < min_stride)
return ERR_PTR(-EINVAL);
ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
if (!ctx)
return ERR_PTR(-ENOMEM);
ctx->regs = regs;
ctx->val_bytes = config->val_bits / 8;
ctx->clk = ERR_PTR(-ENODEV);
switch (regmap_get_val_endian(dev, ®map_mmio, config)) {
case REGMAP_ENDIAN_DEFAULT:
case REGMAP_ENDIAN_LITTLE:
#ifdef __LITTLE_ENDIAN
case REGMAP_ENDIAN_NATIVE:
#endif
switch (config->val_bits) {
case 8:
ctx->reg_read = regmap_mmio_read8;
ctx->reg_write = regmap_mmio_write8;
break;
case 16:
ctx->reg_read = regmap_mmio_read16le;
ctx->reg_write = regmap_mmio_write16le;
break;
case 32:
ctx->reg_read = regmap_mmio_read32le;
ctx->reg_write = regmap_mmio_write32le;
break;
#ifdef CONFIG_64BIT
case 64:
ctx->reg_read = regmap_mmio_read64le;
ctx->reg_write = regmap_mmio_write64le;
break;
#endif
default:
ret = -EINVAL;
goto err_free;
}
break;
case REGMAP_ENDIAN_BIG:
#ifdef __BIG_ENDIAN
case REGMAP_ENDIAN_NATIVE:
#endif
switch (config->val_bits) {
case 8:
ctx->reg_read = regmap_mmio_read8;
ctx->reg_write = regmap_mmio_write8;
break;
case 16:
ctx->reg_read = regmap_mmio_read16be;
ctx->reg_write = regmap_mmio_write16be;
break;
case 32:
ctx->reg_read = regmap_mmio_read32be;
ctx->reg_write = regmap_mmio_write32be;
break;
default:
ret = -EINVAL;
goto err_free;
}
break;
default:
ret = -EINVAL;
goto err_free;
}
if (clk_id == NULL)
return ctx;
ctx->clk = clk_get(dev, clk_id);
if (IS_ERR(ctx->clk)) {
ret = PTR_ERR(ctx->clk);
goto err_free;
}
ret = clk_prepare(ctx->clk);
if (ret < 0) {
clk_put(ctx->clk);
goto err_free;
}
return ctx;
err_free:
kfree(ctx);
return ERR_PTR(ret);
}
. . . . . .
struct regmap *__devm_regmap_init_mmio_clk(struct device *dev,
const char *clk_id,
void __iomem *regs,
const struct regmap_config *config,
struct lock_class_key *lock_key,
const char *lock_name)
{
struct regmap_mmio_context *ctx;
ctx = regmap_mmio_gen_context(dev, clk_id, regs, config);
if (IS_ERR(ctx))
return ERR_CAST(ctx);
return __devm_regmap_init(dev, ®map_mmio, ctx, config,
lock_key, lock_name);
}
EXPORT_SYMBOL_GPL(__devm_regmap_init_mmio_clk);
最终读写设备 IO 寄存器的操作由 context 提供，如这里的 struct regmap_mmio_context。也可以将 context 看作是 struct regmap_bus 的实现。
__regmap_init_mmio_clk() 函数通过 regmap_mmio_gen_context() 函数分配并初始化 context，并调用 __devm_regmap_init() 函数分配并初始化 struct regmap。
regmap_mmio_gen_context() 函数检查寄存器映射配置，并根据配置的寄存器值的位宽，及尾端是大尾端还是小尾端，选择适当的读写操作函数。大尾端不支持 64 位的寄存器读写。最终的读写操作，由各个硬件平台特有的 IO 操作完成。
struct regmap_bus 表示寄存器映射总线，这个结构体的定义 (位于 include/linux/regmap.h) 如下：
struct regmap_async;
typedef int (*regmap_hw_write)(void *context, const void *data,
size_t count);
typedef int (*regmap_hw_gather_write)(void *context,
const void *reg, size_t reg_len,
const void *val, size_t val_len);
typedef int (*regmap_hw_async_write)(void *context,
const void *reg, size_t reg_len,
const void *val, size_t val_len,
struct regmap_async *async);
typedef int (*regmap_hw_read)(void *context,
const void *reg_buf, size_t reg_size,
void *val_buf, size_t val_size);
typedef int (*regmap_hw_reg_read)(void *context, unsigned int reg,
unsigned int *val);
typedef int (*regmap_hw_reg_write)(void *context, unsigned int reg,
unsigned int val);
typedef int (*regmap_hw_reg_update_bits)(void *context, unsigned int reg,
unsigned int mask, unsigned int val);
typedef struct regmap_async *(*regmap_hw_async_alloc)(void);
typedef void (*regmap_hw_free_context)(void *context);
. . . . . .
struct regmap_bus {
bool fast_io;
regmap_hw_write write;
regmap_hw_gather_write gather_write;
regmap_hw_async_write async_write;
regmap_hw_reg_write reg_write;
regmap_hw_reg_update_bits reg_update_bits;
regmap_hw_read read;
regmap_hw_reg_read reg_read;
regmap_hw_free_context free_context;
regmap_hw_async_alloc async_alloc;
u8 read_flag_mask;
enum regmap_endian reg_format_endian_default;
enum regmap_endian val_format_endian_default;
size_t max_raw_read;
size_t max_raw_write;
};
struct regmap_bus 基本上是各种寄存器 IO 操作的集合。对于 mmio，它的 struct regmap_bus 定义 (位于 drivers/base/regmap/regmap-mmio.c) 如下：
static int regmap_mmio_write(void *context, unsigned int reg, unsigned int val)
{
struct regmap_mmio_context *ctx = context;
int ret;
if (!IS_ERR(ctx->clk)) {
ret = clk_enable(ctx->clk);
if (ret < 0)
return ret;
}
ctx->reg_write(ctx, reg, val);
if (!IS_ERR(ctx->clk))
clk_disable(ctx->clk);
return 0;
}
. . . . . .
static int regmap_mmio_read(void *context, unsigned int reg, unsigned int *val)
{
struct regmap_mmio_context *ctx = context;
int ret;
if (!IS_ERR(ctx->clk)) {
ret = clk_enable(ctx->clk);
if (ret < 0)
return ret;
}
*val = ctx->reg_read(ctx, reg);
if (!IS_ERR(ctx->clk))
clk_disable(ctx->clk);
return 0;
}
static void regmap_mmio_free_context(void *context)
{
struct regmap_mmio_context *ctx = context;
if (!IS_ERR(ctx->clk)) {
clk_unprepare(ctx->clk);
if (!ctx->attached_clk)
clk_put(ctx->clk);
}
kfree(context);
}
static const struct regmap_bus regmap_mmio = {
.fast_io = true,
.reg_write = regmap_mmio_write,
.reg_read = regmap_mmio_read,
.free_context = regmap_mmio_free_context,
.val_format_endian_default = REGMAP_ENDIAN_LITTLE,
};
在 regmap 机制中，struct regmap_bus 的角色定位即是完成对硬件设备 IO 寄存器的直接访问。对于 mmio，struct regmap_bus 是通向 context struct regmap_mmio_context 的桥梁。
__devm_regmap_init() 函数定义 (位于 drivers/base/regmap/regmap.c) 如下：
int regmap_attach_dev(struct device *dev, struct regmap *map,
const struct regmap_config *config)
{
struct regmap **m;
int ret;
map->dev = dev;
ret = regmap_set_name(map, config);
if (ret)
return ret;
regmap_debugfs_exit(map);
regmap_debugfs_init(map);
/* Add a devres resource for dev_get_regmap() */
m = devres_alloc(dev_get_regmap_release, sizeof(*m), GFP_KERNEL);
if (!m) {
regmap_debugfs_exit(map);
return -ENOMEM;
}
*m = map;
devres_add(dev, m);
return 0;
}
EXPORT_SYMBOL_GPL(regmap_attach_dev);
. . . . . .
struct regmap *__regmap_init(struct device *dev,
const struct regmap_bus *bus,
void *bus_context,
const struct regmap_config *config,
struct lock_class_key *lock_key,
const char *lock_name)
{
struct regmap *map;
int ret = -EINVAL;
enum regmap_endian reg_endian, val_endian;
int i, j;
if (!config)
goto err;
map = kzalloc(sizeof(*map), GFP_KERNEL);
if (map == NULL) {
ret = -ENOMEM;
goto err;
}
ret = regmap_set_name(map, config);
if (ret)
goto err_map;
ret = -EINVAL; /* Later error paths rely on this */
if (config->disable_locking) {
map->lock = map->unlock = regmap_lock_unlock_none;
map->can_sleep = config->can_sleep;
regmap_debugfs_disable(map);
} else if (config->lock && config->unlock) {
map->lock = config->lock;
map->unlock = config->unlock;
map->lock_arg = config->lock_arg;
map->can_sleep = config->can_sleep;
} else if (config->use_hwlock) {
map->hwlock = hwspin_lock_request_specific(config->hwlock_id);
if (!map->hwlock) {
ret = -ENXIO;
goto err_name;
}
switch (config->hwlock_mode) {
case HWLOCK_IRQSTATE:
map->lock = regmap_lock_hwlock_irqsave;
map->unlock = regmap_unlock_hwlock_irqrestore;
break;
case HWLOCK_IRQ:
map->lock = regmap_lock_hwlock_irq;
map->unlock = regmap_unlock_hwlock_irq;
break;
default:
map->lock = regmap_lock_hwlock;
map->unlock = regmap_unlock_hwlock;
break;
}
map->lock_arg = map;
} else {
if ((bus && bus->fast_io) ||
config->fast_io) {
spin_lock_init(&map->spinlock);
map->lock = regmap_lock_spinlock;
map->unlock = regmap_unlock_spinlock;
lockdep_set_class_and_name(&map->spinlock,
lock_key, lock_name);
} else {
mutex_init(&map->mutex);
map->lock = regmap_lock_mutex;
map->unlock = regmap_unlock_mutex;
map->can_sleep = true;
lockdep_set_class_and_name(&map->mutex,
lock_key, lock_name);
}
map->lock_arg = map;
}
/*
* When we write in fast-paths with regmap_bulk_write() don't allocate
* scratch buffers with sleeping allocations.
*/
if ((bus && bus->fast_io) || config->fast_io)
map->alloc_flags = GFP_ATOMIC;
else
map->alloc_flags = GFP_KERNEL;
map->format.reg_bytes = DIV_ROUND_UP(config->reg_bits, 8);
map->format.pad_bytes = config->pad_bits / 8;
map->format.val_bytes = DIV_ROUND_UP(config->val_bits, 8);
map->format.buf_size = DIV_ROUND_UP(config->reg_bits +
config->val_bits + config->pad_bits, 8);
map->reg_shift = config->pad_bits % 8;
if (config->reg_stride)
map->reg_stride = config->reg_stride;
else
map->reg_stride = 1;
if (is_power_of_2(map->reg_stride))
map->reg_stride_order = ilog2(map->reg_stride);
else
map->reg_stride_order = -1;
map->use_single_read = config->use_single_read || !bus || !bus->read;
map->use_single_write = config->use_single_write || !bus || !bus->write;
map->can_multi_write = config->can_multi_write && bus && bus->write;
if (bus) {
map->max_raw_read = bus->max_raw_read;
map->max_raw_write = bus->max_raw_write;
}
map->dev = dev;
map->bus = bus;
map->bus_context = bus_context;
map->max_register = config->max_register;
map->wr_table = config->wr_table;
map->rd_table = config->rd_table;
map->volatile_table = config->volatile_table;
map->precious_table = config->precious_table;
map->wr_noinc_table = config->wr_noinc_table;
map->rd_noinc_table = config->rd_noinc_table;
map->writeable_reg = config->writeable_reg;
map->readable_reg = config->readable_reg;
map->volatile_reg = config->volatile_reg;
map->precious_reg = config->precious_reg;
map->writeable_noinc_reg = config->writeable_noinc_reg;
map->readable_noinc_reg = config->readable_noinc_reg;
map->cache_type = config->cache_type;
spin_lock_init(&map->async_lock);
INIT_LIST_HEAD(&map->async_list);
INIT_LIST_HEAD(&map->async_free);
init_waitqueue_head(&map->async_waitq);
if (config->read_flag_mask ||
config->write_flag_mask ||
config->zero_flag_mask) {
map->read_flag_mask = config->read_flag_mask;
map->write_flag_mask = config->write_flag_mask;
} else if (bus) {
map->read_flag_mask = bus->read_flag_mask;
}
if (!bus) {
map->reg_read = config->reg_read;
map->reg_write = config->reg_write;
map->defer_caching = false;
goto skip_format_initialization;
} else if (!bus->read || !bus->write) {
map->reg_read = _regmap_bus_reg_read;
map->reg_write = _regmap_bus_reg_write;
map->reg_update_bits = bus->reg_update_bits;
map->defer_caching = false;
goto skip_format_initialization;
} else {
map->reg_read = _regmap_bus_read;
map->reg_update_bits = bus->reg_update_bits;
}
reg_endian = regmap_get_reg_endian(bus, config);
val_endian = regmap_get_val_endian(dev, bus, config);
switch (config->reg_bits + map->reg_shift) {
case 2:
switch (config->val_bits) {
case 6:
map->format.format_write = regmap_format_2_6_write;
break;
default:
goto err_hwlock;
}
break;
case 4:
switch (config->val_bits) {
case 12:
map->format.format_write = regmap_format_4_12_write;
break;
default:
goto err_hwlock;
}
break;
case 7:
switch (config->val_bits) {
case 9:
map->format.format_write = regmap_format_7_9_write;
break;
default:
goto err_hwlock;
}
break;
case 10:
switch (config->val_bits) {
case 14:
map->format.format_write = regmap_format_10_14_write;
break;
default:
goto err_hwlock;
}
break;
case 12:
switch (config->val_bits) {
case 20:
map->format.format_write = regmap_format_12_20_write;
break;
default:
goto err_hwlock;
}
break;
case 8:
map->format.format_reg = regmap_format_8;
break;
case 16:
switch (reg_endian) {
case REGMAP_ENDIAN_BIG:
map->format.format_reg = regmap_format_16_be;
break;
case REGMAP_ENDIAN_LITTLE:
map->format.format_reg = regmap_format_16_le;
break;
case REGMAP_ENDIAN_NATIVE:
map->format.format_reg = regmap_format_16_native;
break;
default:
goto err_hwlock;
}
break;
case 24:
if (reg_endian != REGMAP_ENDIAN_BIG)
goto err_hwlock;
map->format.format_reg = regmap_format_24;
break;
case 32:
switch (reg_endian) {
case REGMAP_ENDIAN_BIG:
map->format.format_reg = regmap_format_32_be;
break;
case REGMAP_ENDIAN_LITTLE:
map->format.format_reg = regmap_format_32_le;
break;
case REGMAP_ENDIAN_NATIVE:
map->format.format_reg = regmap_format_32_native;
break;
default:
goto err_hwlock;
}
break;
#ifdef CONFIG_64BIT
case 64:
switch (reg_endian) {
case REGMAP_ENDIAN_BIG:
map->format.format_reg = regmap_format_64_be;
break;
case REGMAP_ENDIAN_LITTLE:
map->format.format_reg = regmap_format_64_le;
break;
case REGMAP_ENDIAN_NATIVE:
map->format.format_reg = regmap_format_64_native;
break;
default:
goto err_hwlock;
}
break;
#endif
default:
goto err_hwlock;
}
if (val_endian == REGMAP_ENDIAN_NATIVE)
map->format.parse_inplace = regmap_parse_inplace_noop;
switch (config->val_bits) {
case 8:
map->format.format_val = regmap_format_8;
map->format.parse_val = regmap_parse_8;
map->format.parse_inplace = regmap_parse_inplace_noop;
break;
case 16:
switch (val_endian) {
case REGMAP_ENDIAN_BIG:
map->format.format_val = regmap_format_16_be;
map->format.parse_val = regmap_parse_16_be;
map->format.parse_inplace = regmap_parse_16_be_inplace;
break;
case REGMAP_ENDIAN_LITTLE:
map->format.format_val = regmap_format_16_le;
map->format.parse_val = regmap_parse_16_le;
map->format.parse_inplace = regmap_parse_16_le_inplace;
break;
case REGMAP_ENDIAN_NATIVE:
map->format.format_val = regmap_format_16_native;
map->format.parse_val = regmap_parse_16_native;
break;
default:
goto err_hwlock;
}
break;
case 24:
if (val_endian != REGMAP_ENDIAN_BIG)
goto err_hwlock;
map->format.format_val = regmap_format_24;
map->format.parse_val = regmap_parse_24;
break;
case 32:
switch (val_endian) {
case REGMAP_ENDIAN_BIG:
map->format.format_val = regmap_format_32_be;
map->format.parse_val = regmap_parse_32_be;
map->format.parse_inplace = regmap_parse_32_be_inplace;
break;
case REGMAP_ENDIAN_LITTLE:
map->format.format_val = regmap_format_32_le;
map->format.parse_val = regmap_parse_32_le;
map->format.parse_inplace = regmap_parse_32_le_inplace;
break;
case REGMAP_ENDIAN_NATIVE:
map->format.format_val = regmap_format_32_native;
map->format.parse_val = regmap_parse_32_native;
break;
default:
goto err_hwlock;
}
break;
#ifdef CONFIG_64BIT
case 64:
switch (val_endian) {
case REGMAP_ENDIAN_BIG:
map->format.format_val = regmap_format_64_be;
map->format.parse_val = regmap_parse_64_be;
map->format.parse_inplace = regmap_parse_64_be_inplace;
break;
case REGMAP_ENDIAN_LITTLE:
map->format.format_val = regmap_format_64_le;
map->format.parse_val = regmap_parse_64_le;
map->format.parse_inplace = regmap_parse_64_le_inplace;
break;
case REGMAP_ENDIAN_NATIVE:
map->format.format_val = regmap_format_64_native;
map->format.parse_val = regmap_parse_64_native;
break;
default:
goto err_hwlock;
}
break;
#endif
}
if (map->format.format_write) {
if ((reg_endian != REGMAP_ENDIAN_BIG) ||
(val_endian != REGMAP_ENDIAN_BIG))
goto err_hwlock;
map->use_single_write = true;
}
if (!map->format.format_write &&
!(map->format.format_reg && map->format.format_val))
goto err_hwlock;
map->work_buf = kzalloc(map->format.buf_size, GFP_KERNEL);
if (map->work_buf == NULL) {
ret = -ENOMEM;
goto err_hwlock;
}
if (map->format.format_write) {
map->defer_caching = false;
map->reg_write = _regmap_bus_formatted_write;
} else if (map->format.format_val) {
map->defer_caching = true;
map->reg_write = _regmap_bus_raw_write;
}
skip_format_initialization:
map->range_tree = RB_ROOT;
for (i = 0; i < config->num_ranges; i++) {
const struct regmap_range_cfg *range_cfg = &config->ranges[i];
struct regmap_range_node *new;
/* Sanity check */
if (range_cfg->range_max < range_cfg->range_min) {
dev_err(map->dev, "Invalid range %d: %d < %d\n", i,
range_cfg->range_max, range_cfg->range_min);
goto err_range;
}
if (range_cfg->range_max > map->max_register) {
dev_err(map->dev, "Invalid range %d: %d > %d\n", i,
range_cfg->range_max, map->max_register);
goto err_range;
}
if (range_cfg->selector_reg > map->max_register) {
dev_err(map->dev,
"Invalid range %d: selector out of map\n", i);
goto err_range;
}
if (range_cfg->window_len == 0) {
dev_err(map->dev, "Invalid range %d: window_len 0\n",
i);
goto err_range;
}
/* Make sure, that this register range has no selector
or data window within its boundary */
for (j = 0; j < config->num_ranges; j++) {
unsigned sel_reg = config->ranges[j].selector_reg;
unsigned win_min = config->ranges[j].window_start;
unsigned win_max = win_min +
config->ranges[j].window_len - 1;
/* Allow data window inside its own virtual range */
if (j == i)
continue;
if (range_cfg->range_min <= sel_reg &&
sel_reg <= range_cfg->range_max) {
dev_err(map->dev,
"Range %d: selector for %d in window\n",
i, j);
goto err_range;
}
if (!(win_max < range_cfg->range_min ||
win_min > range_cfg->range_max)) {
dev_err(map->dev,
"Range %d: window for %d in window\n",
i, j);
goto err_range;
}
}
new = kzalloc(sizeof(*new), GFP_KERNEL);
if (new == NULL) {
ret = -ENOMEM;
goto err_range;
}
new->map = map;
new->name = range_cfg->name;
new->range_min = range_cfg->range_min;
new->range_max = range_cfg->range_max;
new->selector_reg = range_cfg->selector_reg;
new->selector_mask = range_cfg->selector_mask;
new->selector_shift = range_cfg->selector_shift;
new->window_start = range_cfg->window_start;
new->window_len = range_cfg->window_len;
if (!_regmap_range_add(map, new)) {
dev_err(map->dev, "Failed to add range %d\n", i);
kfree(new);
goto err_range;
}
if (map->selector_work_buf == NULL) {
map->selector_work_buf =
kzalloc(map->format.buf_size, GFP_KERNEL);
if (map->selector_work_buf == NULL) {
ret = -ENOMEM;
goto err_range;
}
}
}
ret = regcache_init(map, config);
if (ret != 0)
goto err_range;
if (dev) {
ret = regmap_attach_dev(dev, map, config);
if (ret != 0)
goto err_regcache;
} else {
regmap_debugfs_init(map);
}
return map;
err_regcache:
regcache_exit(map);
err_range:
regmap_range_exit(map);
kfree(map->work_buf);
err_hwlock:
if (map->hwlock)
hwspin_lock_free(map->hwlock);
err_name:
kfree_const(map->name);
err_map:
kfree(map);
err:
return ERR_PTR(ret);
}
EXPORT_SYMBOL_GPL(__regmap_init);
static void devm_regmap_release(struct device *dev, void *res)
{
regmap_exit(*(struct regmap **)res);
}
struct regmap *__devm_regmap_init(struct device *dev,
const struct regmap_bus *bus,
void *bus_context,
const struct regmap_config *config,
struct lock_class_key *lock_key,
const char *lock_name)
{
struct regmap **ptr, *regmap;
ptr = devres_alloc(devm_regmap_release, sizeof(*ptr), GFP_KERNEL);
if (!ptr)
return ERR_PTR(-ENOMEM);
regmap = __regmap_init(dev, bus, bus_context, config,
lock_key, lock_name);
if (!IS_ERR(regmap)) {
*ptr = regmap;
devres_add(dev, ptr);
} else {
devres_free(ptr);
}
return regmap;
}
EXPORT_SYMBOL_GPL(__devm_regmap_init);
__devm_regmap_init() 函数通过 __regmap_init() 函数创建并初始化 struct regmap 对象，并创建 devres 来维护 struct regmap 对象的生命周期，使得它可以随着 struct device 对象的生命周期的结束而结束。
__regmap_init() 函数比较长，但它做的事情比较清晰：
- 分配
struct regmap对象。 - 根据寄存器映射配置选择
lock/unlock操作。 - 根据传入的寄存器映射配置、
regmap_bus和bus_context等初始化struct regmap对象。 - 根据传入的寄存器映射配置和
regmap_bus等选择设备 IO 寄存器的读写操作。 - 根据传入的寄存器映射配置选择格式化的寄存器操作。
- 处理寄存器映射范围。
- 初始化寄存器映射缓存。
- 连接 dev，这包括初始化 debugfs 等。
regcache_init() 函数初始化寄存器映射缓存，它的定义 (位于 drivers/base/regmap/regcache.c) 如下：
static const struct regcache_ops *cache_types[] = {
®cache_rbtree_ops,
#if IS_ENABLED(CONFIG_REGCACHE_COMPRESSED)
®cache_lzo_ops,
#endif
®cache_flat_ops,
};
. . . . . .
int regcache_init(struct regmap *map, const struct regmap_config *config)
{
int ret;
int i;
void *tmp_buf;
if (map->cache_type == REGCACHE_NONE) {
if (config->reg_defaults || config->num_reg_defaults_raw)
dev_warn(map->dev,
"No cache used with register defaults set!\n");
map->cache_bypass = true;
return 0;
}
if (config->reg_defaults && !config->num_reg_defaults) {
dev_err(map->dev,
"Register defaults are set without the number!\n");
return -EINVAL;
}
for (i = 0; i < config->num_reg_defaults; i++)
if (config->reg_defaults[i].reg % map->reg_stride)
return -EINVAL;
for (i = 0; i < ARRAY_SIZE(cache_types); i++)
if (cache_types[i]->type == map->cache_type)
break;
if (i == ARRAY_SIZE(cache_types)) {
dev_err(map->dev, "Could not match compress type: %d\n",
map->cache_type);
return -EINVAL;
}
map->num_reg_defaults = config->num_reg_defaults;
map->num_reg_defaults_raw = config->num_reg_defaults_raw;
map->reg_defaults_raw = config->reg_defaults_raw;
map->cache_word_size = DIV_ROUND_UP(config->val_bits, 8);
map->cache_size_raw = map->cache_word_size * config->num_reg_defaults_raw;
map->cache = NULL;
map->cache_ops = cache_types[i];
if (!map->cache_ops->read ||
!map->cache_ops->write ||
!map->cache_ops->name)
return -EINVAL;
/* We still need to ensure that the reg_defaults
* won't vanish from under us. We'll need to make
* a copy of it.
*/
if (config->reg_defaults) {
tmp_buf = kmemdup(config->reg_defaults, map->num_reg_defaults *
sizeof(struct reg_default), GFP_KERNEL);
if (!tmp_buf)
return -ENOMEM;
map->reg_defaults = tmp_buf;
} else if (map->num_reg_defaults_raw) {
/* Some devices such as PMICs don't have cache defaults,
* we cope with this by reading back the HW registers and
* crafting the cache defaults by hand.
*/
ret = regcache_hw_init(map);
if (ret < 0)
return ret;
if (map->cache_bypass)
return 0;
}
if (!map->max_register)
map->max_register = map->num_reg_defaults_raw;
if (map->cache_ops->init) {
dev_dbg(map->dev, "Initializing %s cache\n",
map->cache_ops->name);
ret = map->cache_ops->init(map);
if (ret)
goto err_free;
}
return 0;
err_free:
kfree(map->reg_defaults);
if (map->cache_free)
kfree(map->reg_defaults_raw);
return ret;
}
这个函数根据传入的配置的缓存类型，选择适当的 struct regcache_ops，并初始化缓存。struct regcache_ops 定义 (位于 drivers/base/regmap/internal.h) 如下：
struct regcache_ops {
const char *name;
enum regcache_type type;
int (*init)(struct regmap *map);
int (*exit)(struct regmap *map);
#ifdef CONFIG_DEBUG_FS
void (*debugfs_init)(struct regmap *map);
#endif
int (*read)(struct regmap *map, unsigned int reg, unsigned int *value);
int (*write)(struct regmap *map, unsigned int reg, unsigned int value);
int (*sync)(struct regmap *map, unsigned int min, unsigned int max);
int (*drop)(struct regmap *map, unsigned int min, unsigned int max);
};
struct regmap 的定义 (位于 drivers/base/regmap/internal.h) 如下：
struct regmap {
union {
struct mutex mutex;
struct {
spinlock_t spinlock;
unsigned long spinlock_flags;
};
};
regmap_lock lock;
regmap_unlock unlock;
void *lock_arg; /* This is passed to lock/unlock functions */
gfp_t alloc_flags;
struct device *dev; /* Device we do I/O on */
void *work_buf; /* Scratch buffer used to format I/O */
struct regmap_format format; /* Buffer format */
const struct regmap_bus *bus;
void *bus_context;
const char *name;
bool async;
spinlock_t async_lock;
wait_queue_head_t async_waitq;
struct list_head async_list;
struct list_head async_free;
int async_ret;
#ifdef CONFIG_DEBUG_FS
bool debugfs_disable;
struct dentry *debugfs;
const char *debugfs_name;
unsigned int debugfs_reg_len;
unsigned int debugfs_val_len;
unsigned int debugfs_tot_len;
struct list_head debugfs_off_cache;
struct mutex cache_lock;
#endif
unsigned int max_register;
bool (*writeable_reg)(struct device *dev, unsigned int reg);
bool (*readable_reg)(struct device *dev, unsigned int reg);
bool (*volatile_reg)(struct device *dev, unsigned int reg);
bool (*precious_reg)(struct device *dev, unsigned int reg);
bool (*writeable_noinc_reg)(struct device *dev, unsigned int reg);
bool (*readable_noinc_reg)(struct device *dev, unsigned int reg);
const struct regmap_access_table *wr_table;
const struct regmap_access_table *rd_table;
const struct regmap_access_table *volatile_table;
const struct regmap_access_table *precious_table;
const struct regmap_access_table *wr_noinc_table;
const struct regmap_access_table *rd_noinc_table;
int (*reg_read)(void *context, unsigned int reg, unsigned int *val);
int (*reg_write)(void *context, unsigned int reg, unsigned int val);
int (*reg_update_bits)(void *context, unsigned int reg,
unsigned int mask, unsigned int val);
bool defer_caching;
unsigned long read_flag_mask;
unsigned long write_flag_mask;
/* number of bits to (left) shift the reg value when formatting*/
int reg_shift;
int reg_stride;
int reg_stride_order;
/* regcache specific members */
const struct regcache_ops *cache_ops;
enum regcache_type cache_type;
/* number of bytes in reg_defaults_raw */
unsigned int cache_size_raw;
/* number of bytes per word in reg_defaults_raw */
unsigned int cache_word_size;
/* number of entries in reg_defaults */
unsigned int num_reg_defaults;
/* number of entries in reg_defaults_raw */
unsigned int num_reg_defaults_raw;
/* if set, only the cache is modified not the HW */
bool cache_only;
/* if set, only the HW is modified not the cache */
bool cache_bypass;
/* if set, remember to free reg_defaults_raw */
bool cache_free;
struct reg_default *reg_defaults;
const void *reg_defaults_raw;
void *cache;
/* if set, the cache contains newer data than the HW */
bool cache_dirty;
/* if set, the HW registers are known to match map->reg_defaults */
bool no_sync_defaults;
struct reg_sequence *patch;
int patch_regs;
/* if set, converts bulk read to single read */
bool use_single_read;
/* if set, converts bulk write to single write */
bool use_single_write;
/* if set, the device supports multi write mode */
bool can_multi_write;
/* if set, raw reads/writes are limited to this size */
size_t max_raw_read;
size_t max_raw_write;
struct rb_root range_tree;
void *selector_work_buf; /* Scratch buffer used for selector */
struct hwspinlock *hwlock;
/* if set, the regmap core can sleep */
bool can_sleep;
};
struct regmap 是 struct regmap_config、struct regmap_bus 和 cached 三者的结合，它通过 struct regmap_config 连接具体设备的寄存器的信息，通过 struct regmap_bus 连接对具体设备的 IO 寄存器的读写操作，通过 cached 连接缓存。
Done.