2.1 检查结构体struct spi_nor是否合格，匹配支持的nor flash ID得到info
2.2 初始化结构体struct spi_nor_flash_parameter变量params
1. 简介
前面已经介绍了spi-nor子系统的由来，现在我们来看看spi-nor子系统的代码。spi-nor的核心结构体是以下代码：
struct spi_nor {
struct mtd_info mtd;
struct mutex lock;
struct device *dev;
u32 page_size;
u8 addr_width;
u8 erase_opcode;
u8 read_opcode;
u8 read_dummy;
u8 program_opcode;
enum spi_nor_protocol read_proto;
enum spi_nor_protocol write_proto;
enum spi_nor_protocol reg_proto;
bool sst_write_second;
u32 flags;
u8 cmd_buf[SPI_NOR_MAX_CMD_SIZE];
int (*prepare)(struct spi_nor *nor, enum spi_nor_ops ops);
void (*unprepare)(struct spi_nor *nor, enum spi_nor_ops ops);
int (*read_reg)(struct spi_nor *nor, u8 opcode, u8 *buf, int len);
int (*write_reg)(struct spi_nor *nor, u8 opcode, u8 *buf, int len);
ssize_t (*read)(struct spi_nor *nor, loff_t from,
size_t len, u_char *read_buf);
ssize_t (*write)(struct spi_nor *nor, loff_t to,
size_t len, const u_char *write_buf);
int (*erase)(struct spi_nor *nor, loff_t offs);
int (*flash_lock)(struct spi_nor *nor, loff_t ofs, uint64_t len);
int (*flash_unlock)(struct spi_nor *nor, loff_t ofs, uint64_t len);
int (*flash_is_locked)(struct spi_nor *nor, loff_t ofs, uint64_t len);
void *priv;
};mtd: 指向mtd_info结构体，我们知道所有的存储设备，最终都有可以挂载到mtd子系统中。
lock: 读/写/擦除/锁定/解锁操作的锁定
dev: 指向spi设备或spi nor控制器设备。
page_size: SPI NOR的页面大小
addr_width: 地址字节数
erase_opcode: 用于擦除扇区的操作码
read_opcode: 读操作码
read_dummy: 读取操作所需的dummy数
program_opcode: program操作码
sst_write_second: used by the SST write operation
flags: 当前SPI-NOR的标志选项（SNOR\u F\ux*）。
read_proto: 用于读取操作的SPI协议
write_proto: 用于写操作的SPI协议
reg_proto 用于读\写\擦除操作的SPI协议
cmd_buf: used by the write_reg
这里有一个enum spi_nor_protocol说明一下，如下所示。
enum spi_nor_protocol {
SNOR_PROTO_1_1_1 = SNOR_PROTO_STR(1, 1, 1),
SNOR_PROTO_1_1_2 = SNOR_PROTO_STR(1, 1, 2),
SNOR_PROTO_1_1_4 = SNOR_PROTO_STR(1, 1, 4),
SNOR_PROTO_1_1_8 = SNOR_PROTO_STR(1, 1, 8),
SNOR_PROTO_1_2_2 = SNOR_PROTO_STR(1, 2, 2),
SNOR_PROTO_1_4_4 = SNOR_PROTO_STR(1, 4, 4),
SNOR_PROTO_1_8_8 = SNOR_PROTO_STR(1, 8, 8),
SNOR_PROTO_2_2_2 = SNOR_PROTO_STR(2, 2, 2),
SNOR_PROTO_4_4_4 = SNOR_PROTO_STR(4, 4, 4),
SNOR_PROTO_8_8_8 = SNOR_PROTO_STR(8, 8, 8),
SNOR_PROTO_1_1_1_DTR = SNOR_PROTO_DTR(1, 1, 1),
SNOR_PROTO_1_2_2_DTR = SNOR_PROTO_DTR(1, 2, 2),
SNOR_PROTO_1_4_4_DTR = SNOR_PROTO_DTR(1, 4, 4),
SNOR_PROTO_1_8_8_DTR = SNOR_PROTO_DTR(1, 8, 8),
};这个协议是该spi-nor所使用的协议，是1线、4线、8线等协议，初始值就是默认值。
查看include\linux\mtd\spi-nor.h文件，只有一个对外开放的函数spi_nor_scan，这个也是我们分析的重点。
/**
* spi_nor_scan() - scan the SPI NOR
* @nor: the spi_nor structure
* @name: the chip type name
* @hwcaps: the hardware capabilities supported by the controller driver
*
* The drivers can use this fuction to scan the SPI NOR.
* In the scanning, it will try to get all the necessary information to
* fill the mtd_info{} and the spi_nor{}.
*
* The chip type name can be provided through the @name parameter.
*
* Return: 0 for success, others for failure.
*/
int spi_nor_scan(struct spi_nor *nor, const char *name,
const struct spi_nor_hwcaps *hwcaps);可以看出，对于spi-nor子系统来说，结构体struct spi_nor和struct spi_nor_hwcaps是最主要的设置目标，这个先不管。spi-nor子系统会根据这两个结构体来进行设置一些东西。下面具体分析这个函数。
2. spi_nor_scan
这个函数比较长，我们分几段来看。
2.1 检查结构体struct spi_nor是否合格，匹配支持的nor flash ID得到info
int spi_nor_scan(struct spi_nor *nor, const char *name,
const struct spi_nor_hwcaps *hwcaps)
{
struct spi_nor_flash_parameter params;
const struct flash_info *info = NULL;
struct device *dev = nor->dev;
struct mtd_info *mtd = &nor->mtd;
struct device_node *np = spi_nor_get_flash_node(nor);
int ret;
int i;
ret = spi_nor_check(nor);
if (ret)
return ret;
/* Reset SPI protocol for all commands. */
nor->reg_proto = SNOR_PROTO_1_1_1;
nor->read_proto = SNOR_PROTO_1_1_1;
nor->write_proto = SNOR_PROTO_1_1_1;
if (name)
info = spi_nor_match_id(name);
/* Try to auto-detect if chip name wasn't specified or not found */
if (!info)
info = spi_nor_read_id(nor);
if (IS_ERR_OR_NULL(info))
return -ENOENT;
........
}检查结构体struct spi_nor是否合格，设置读写的协议为SNOR_PROTO_1_1_1，匹配支持的nor flash ID得到info。
2.1.1 spi_nor_check
static int spi_nor_check(struct spi_nor *nor)
{
if (!nor->dev || !nor->read || !nor->write ||
!nor->read_reg || !nor->write_reg) {
pr_err("spi-nor: please fill all the necessary fields!\n");
return -EINVAL;
}
return 0;
}spi_nor_check函数主要检查上层函数传递下来的变量是否设置了必要的变量，这些是编写驱动必须要实现的部分。
2.1.2 spi_nor_read_id
static const struct flash_info *spi_nor_read_id(struct spi_nor *nor)
{
int tmp;
u8 id[SPI_NOR_MAX_ID_LEN];
const struct flash_info *info;
tmp = nor->read_reg(nor, SPINOR_OP_RDID, id, SPI_NOR_MAX_ID_LEN);
if (tmp < 0) {
dev_dbg(nor->dev, "error %d reading JEDEC ID\n", tmp);
return ERR_PTR(tmp);
}
for (tmp = 0; tmp < ARRAY_SIZE(spi_nor_ids) - 1; tmp++) {
info = &spi_nor_ids[tmp];
if (info->id_len) {
if (!memcmp(info->id, id, info->id_len))
return &spi_nor_ids[tmp];
}
}
dev_err(nor->dev, "unrecognized JEDEC id bytes: %02x, %02x, %02x\n",
id[0], id[1], id[2]);
return ERR_PTR(-ENODEV);
}通过调用控制器提供的read_reg函数，读取flash的JEDEC ID，并且从spi_nor_ids匹配是否支持该flash。我们简单看看spi_nor_ids这个全局变量。
static const struct flash_info spi_nor_ids[] = {
.........
{
"gd25q128", INFO(0xc84018, 0, 64 * 1024, 256,
SECT_4K | SPI_NOR_DUAL_READ | SPI_NOR_QUAD_READ |
SPI_NOR_HAS_LOCK | SPI_NOR_HAS_TB)
},
......
};宏INFO定义如下：
宏INFO定义如下。
#define INFO(_jedec_id, _ext_id, _sector_size, _n_sectors, _flags) \
.id = { \
((_jedec_id) >> 16) & 0xff, \
((_jedec_id) >> 8) & 0xff, \
(_jedec_id) & 0xff, \
((_ext_id) >> 8) & 0xff, \
(_ext_id) & 0xff, \
}, \
.id_len = (!(_jedec_id) ? 0 : (3 + ((_ext_id) ? 2 : 0))), \
.sector_size = (_sector_size), \
.n_sectors = (_n_sectors), \
.page_size = 256, \
.flags = (_flags),
我们以gd25q128这个flash为例，最终的展开是：
static const struct flash_info spi_nor_ids[] = {
.........
{
"gd25q128",
.id = {c8,40,18,0,0},
.id_len = 3,
.sector_size = 64 * 1024,
.n_sectors = 256,
.page_size = 256,
.flag = SECT_4K | SPI_NOR_DUAL_READ | SPI_NOR_QUAD_READ |
SPI_NOR_HAS_LOCK | SPI_NOR_HAS_TB
},
......
};2.1.3 struct flash_info
从2.1.2小节我们可以看出，如果我们要写一个nor flash的驱动，我们必须把这个nor flash的基本信息填充到spi_nor_ids这个数组中。下面我们看一下这个结构体，具体的分析我们下面在做。
struct flash_info {
char *name;
/*
* This array stores the ID bytes.
* The first three bytes are the JEDIC ID.
* JEDEC ID zero means "no ID" (mostly older chips).
*/
u8 id[SPI_NOR_MAX_ID_LEN];
u8 id_len;
/* The size listed here is what works with SPINOR_OP_SE, which isn't
* necessarily called a "sector" by the vendor.
*/
unsigned sector_size;
u16 n_sectors;
u16 page_size;
u16 addr_width;
u16 flags;
#define SECT_4K BIT(0) /* SPINOR_OP_BE_4K works uniformly */
#define SPI_NOR_NO_ERASE BIT(1) /* No erase command needed */
#define SST_WRITE BIT(2) /* use SST byte programming */
#define SPI_NOR_NO_FR BIT(3) /* Can't do fastread */
#define SECT_4K_PMC BIT(4) /* SPINOR_OP_BE_4K_PMC works uniformly */
#define SPI_NOR_DUAL_READ BIT(5) /* Flash supports Dual Read */
#define SPI_NOR_QUAD_READ BIT(6) /* Flash supports Quad Read */
#define USE_FSR BIT(7) /* use flag status register */
#define SPI_NOR_HAS_LOCK BIT(8) /* Flash supports lock/unlock via SR */
#define SPI_NOR_HAS_TB BIT(9) /*
* Flash SR has Top/Bottom (TB) protect
* bit. Must be used with
* SPI_NOR_HAS_LOCK.
*/
#define SPI_S3AN BIT(10) /*
* Xilinx Spartan 3AN In-System Flash
* (MFR cannot be used for probing
* because it has the same value as
* ATMEL flashes)
*/
#define SPI_NOR_4B_OPCODES BIT(11) /*
* Use dedicated 4byte address op codes
* to support memory size above 128Mib.
*/
#define NO_CHIP_ERASE BIT(12) /* Chip does not support chip erase */
#define SPI_NOR_SKIP_SFDP BIT(13) /* Skip parsing of SFDP tables */
#define USE_CLSR BIT(14) /* use CLSR command */
#define SPI_NOR_OCTAL_READ BIT(15) /* Flash supports Octal Read */
};2.2 初始化结构体struct spi_nor_flash_parameter变量params
int spi_nor_scan(struct spi_nor *nor, const char *name,
const struct spi_nor_hwcaps *hwcaps)
{
struct spi_nor_flash_parameter params;
........
/*
* Make sure the XSR_RDY flag is set before calling
* spi_nor_wait_till_ready(). Xilinx S3AN share MFR
* with Atmel spi-nor
*/
if (info->flags & SPI_S3AN)
nor->flags |= SNOR_F_READY_XSR_RDY;
/* Parse the Serial Flash Discoverable Parameters table. */
ret = spi_nor_init_params(nor, info, ¶ms);
if (ret)
return ret;
.......
ret = spi_nor_setup(nor, info, ¶ms, hwcaps);
.......
}根据2.1节得到的flash info信息，设置初始化params。
struct spi_nor_flash_parameter {
u64 size;
u32 page_size;
struct spi_nor_hwcaps hwcaps;
struct spi_nor_read_command reads[SNOR_CMD_READ_MAX];
struct spi_nor_pp_command page_programs[SNOR_CMD_PP_MAX];
int (*quad_enable)(struct spi_nor *nor);
};
static int spi_nor_init_params(struct spi_nor *nor,
const struct flash_info *info,
struct spi_nor_flash_parameter *params)
{
/* Set legacy flash parameters as default. */
memset(params, 0, sizeof(*params));
/* Set SPI NOR sizes. */
params->size = (u64)info->sector_size * info->n_sectors;
params->page_size = info->page_size;
/* (Fast) Read settings. */
params->hwcaps.mask |= SNOR_HWCAPS_READ;
spi_nor_set_read_settings(¶ms->reads[SNOR_CMD_READ],
0, 0, SPINOR_OP_READ,
SNOR_PROTO_1_1_1);
if (!(info->flags & SPI_NOR_NO_FR)) {
params->hwcaps.mask |= SNOR_HWCAPS_READ_FAST;
spi_nor_set_read_settings(¶ms->reads[SNOR_CMD_READ_FAST],
0, 8, SPINOR_OP_READ_FAST,
SNOR_PROTO_1_1_1);
}
if (info->flags & SPI_NOR_DUAL_READ) {
params->hwcaps.mask |= SNOR_HWCAPS_READ_1_1_2;
spi_nor_set_read_settings(¶ms->reads[SNOR_CMD_READ_1_1_2],
0, 8, SPINOR_OP_READ_1_1_2,
SNOR_PROTO_1_1_2);
}
if (info->flags & SPI_NOR_QUAD_READ) {
params->hwcaps.mask |= SNOR_HWCAPS_READ_1_1_4;
spi_nor_set_read_settings(¶ms->reads[SNOR_CMD_READ_1_1_4],
0, 8, SPINOR_OP_READ_1_1_4,
SNOR_PROTO_1_1_4);
}
if (info->flags & SPI_NOR_OCTAL_READ) {
params->hwcaps.mask |= SNOR_HWCAPS_READ_1_1_8;
spi_nor_set_read_settings(¶ms->reads[SNOR_CMD_READ_1_1_8],
0, 8, SPINOR_OP_READ_1_1_8,
SNOR_PROTO_1_1_8);
}
/* Page Program settings. */
params->hwcaps.mask |= SNOR_HWCAPS_PP;
spi_nor_set_pp_settings(¶ms->page_programs[SNOR_CMD_PP],
SPINOR_OP_PP, SNOR_PROTO_1_1_1);
/* Select the procedure to set the Quad Enable bit. */
if (params->hwcaps.mask & (SNOR_HWCAPS_READ_QUAD |
SNOR_HWCAPS_PP_QUAD)) {
switch (JEDEC_MFR(info)) {
case SNOR_MFR_MACRONIX:
params->quad_enable = macronix_quad_enable;
break;
case SNOR_MFR_MICRON:
break;
case SNOR_MFR_GIGADEVICE:
params->quad_enable = spansion_read_cr_quad_enable;
break;
default:
/* Kept only for backward compatibility purpose. */
params->quad_enable = spansion_quad_enable;
break;
}
}
/* Override the parameters with data read from SFDP tables. */
nor->addr_width = 0;
nor->mtd.erasesize = 0;
if ((info->flags & (SPI_NOR_DUAL_READ | SPI_NOR_QUAD_READ | SPI_NOR_OCTAL_READ)) &&
!(info->flags & SPI_NOR_SKIP_SFDP)) {
struct spi_nor_flash_parameter sfdp_params;
memcpy(&sfdp_params, params, sizeof(sfdp_params));
if (spi_nor_parse_sfdp(nor, &sfdp_params)) {
nor->addr_width = 0;
nor->mtd.erasesize = 0;
} else {
memcpy(params, &sfdp_params, sizeof(*params));
}
}
return 0;
}这个比较简单，根据flag的标志，设置params中的变量，主要设置的是该nor flash的硬件能力集。例如，上面的例子中我们的flash info的flag为
.flag = SECT_4K | SPI_NOR_DUAL_READ | SPI_NOR_QUAD_READ |
SPI_NOR_HAS_LOCK | SPI_NOR_HAS_TB有一个地方需要注意的是，使能Quad Enable bit位。
/* Select the procedure to set the Quad Enable bit. */
if (params->hwcaps.mask & (SNOR_HWCAPS_READ_QUAD |
SNOR_HWCAPS_PP_QUAD)) {
switch (JEDEC_MFR(info)) {
case SNOR_MFR_MACRONIX:
params->quad_enable = macronix_quad_enable;
break;
case SNOR_MFR_MICRON:
break;
case SNOR_MFR_GIGADEVICE:
params->quad_enable = spansion_read_cr_quad_enable;
break;
default:
/* Kept only for backward compatibility purpose. */
params->quad_enable = spansion_quad_enable;
break;
}
}read sfdp相关信息。
/* Override the parameters with data read from SFDP tables. */
nor->addr_width = 0;
nor->mtd.erasesize = 0;
if ((info->flags & (SPI_NOR_DUAL_READ | SPI_NOR_QUAD_READ | SPI_NOR_OCTAL_READ)) &&
!(info->flags & SPI_NOR_SKIP_SFDP)) {
struct spi_nor_flash_parameter sfdp_params;
memcpy(&sfdp_params, params, sizeof(sfdp_params));
if (spi_nor_parse_sfdp(nor, &sfdp_params)) {
nor->addr_width = 0;
nor->mtd.erasesize = 0;
} else {
memcpy(params, &sfdp_params, sizeof(*params));
}
}
2.3 设置保护bit、mtd相关的结构体
int spi_nor_scan(struct spi_nor *nor, const char *name,
const struct spi_nor_hwcaps *hwcaps)
{
.....
/*
* Atmel, SST, Intel/Numonyx, and others serial NOR tend to power up
* with the software protection bits set
*/
if (JEDEC_MFR(info) == SNOR_MFR_ATMEL ||
JEDEC_MFR(info) == SNOR_MFR_INTEL ||
JEDEC_MFR(info) == SNOR_MFR_SST ||
info->flags & SPI_NOR_HAS_LOCK) {
write_enable(nor);
write_sr(nor, 0);
spi_nor_wait_till_ready(nor);
}
if (!mtd->name)
mtd->name = dev_name(dev);
mtd->priv = nor;
mtd->type = MTD_NORFLASH;
mtd->writesize = 1;
mtd->flags = MTD_CAP_NORFLASH;
mtd->size = params.size;
mtd->_erase = spi_nor_erase;
mtd->_read = spi_nor_read;
/* NOR protection support for STmicro/Micron chips and similar */
if (JEDEC_MFR(info) == SNOR_MFR_MICRON ||
info->flags & SPI_NOR_HAS_LOCK) {
nor->flash_lock = stm_lock;
nor->flash_unlock = stm_unlock;
nor->flash_is_locked = stm_is_locked;
}
if (nor->flash_lock && nor->flash_unlock && nor->flash_is_locked) {
mtd->_lock = spi_nor_lock;
mtd->_unlock = spi_nor_unlock;
mtd->_is_locked = spi_nor_is_locked;
}
/* sst nor chips use AAI word program */
if (info->flags & SST_WRITE)
mtd->_write = sst_write;
else
mtd->_write = spi_nor_write;
if (info->flags & USE_FSR)
nor->flags |= SNOR_F_USE_FSR;
if (info->flags & SPI_NOR_HAS_TB)
nor->flags |= SNOR_F_HAS_SR_TB;
if (info->flags & NO_CHIP_ERASE)
nor->flags |= SNOR_F_NO_OP_CHIP_ERASE;
if (info->flags & USE_CLSR)
nor->flags |= SNOR_F_USE_CLSR;
if (info->flags & SPI_NOR_NO_ERASE)
mtd->flags |= MTD_NO_ERASE;
mtd->dev.parent = dev;
nor->page_size = params.page_size;
mtd->writebufsize = nor->page_size;
if (np) {
/* If we were instantiated by DT, use it */
if (of_property_read_bool(np, "m25p,fast-read"))
params.hwcaps.mask |= SNOR_HWCAPS_READ_FAST;
else
params.hwcaps.mask &= ~SNOR_HWCAPS_READ_FAST;
} else {
/* If we weren't instantiated by DT, default to fast-read */
params.hwcaps.mask |= SNOR_HWCAPS_READ_FAST;
}
/* Some devices cannot do fast-read, no matter what DT tells us */
if (info->flags & SPI_NOR_NO_FR)
params.hwcaps.mask &= ~SNOR_HWCAPS_READ_FAST;
....
}2.4 spi_nor_setup
int spi_nor_scan(struct spi_nor *nor, const char *name,
const struct spi_nor_hwcaps *hwcaps)
{
.....
/*
* Configure the SPI memory:
* - select op codes for (Fast) Read, Page Program and Sector Erase.
* - set the number of dummy cycles (mode cycles + wait states).
* - set the SPI protocols for register and memory accesses.
* - set the Quad Enable bit if needed (required by SPI x-y-4 protos).
*/
ret = spi_nor_setup(nor, info, ¶ms, hwcaps);
.......
}2.5 设置地址宽度
int spi_nor_scan(struct spi_nor *nor, const char *name,
const struct spi_nor_hwcaps *hwcaps)
{
.....
if (nor->addr_width) {
/* already configured from SFDP */
} else if (info->addr_width) {
nor->addr_width = info->addr_width;
} else if (mtd->size > 0x1000000) {
/* enable 4-byte addressing if the device exceeds 16MiB */
nor->addr_width = 4;
if (JEDEC_MFR(info) == SNOR_MFR_SPANSION ||
info->flags & SPI_NOR_4B_OPCODES)
spi_nor_set_4byte_opcodes(nor, info);
else
set_4byte(nor, info, 1);
} else {
nor->addr_width = 3;
}
.......
}如果nor flash的大小超过16M，那么必须使用4根地址线才能访问全部的flash空间。
2.6 s3an_nor_scan
int spi_nor_scan(struct spi_nor *nor, const char *name,
const struct spi_nor_hwcaps *hwcaps)
{
.....
if (info->flags & SPI_S3AN) {
ret = s3an_nor_scan(info, nor);
if (ret)
return ret;
}
.......
}s3an_nor_scan后面再说。