我的經歷：
看了某些大神的說明，我膽怯地進入了drivers/mmc/host/。
由於用的是s3c2440，看驅動時，我首先會找s3c字樣，於是我注意到sdhci-s3c.c和s3cmci.c。
看了一下Kconfig
config MMC_S3C
tristate "Samsung S3C SD/MMC Card Interface support"
depends on ARCH_S3C2410
help
This selects a driver for the MCI interface found in
Samsung's S3C2410, S3C2412, S3C2440, S3C2442 CPUs.
If you have a board based on one of those and a MMC/SD
slot, say Y or M here.
If unsure, say N.
再看Makefile
obj-$(CONFIG_MMC_S3C) += s3cmci.o
我想我用s3cmci就可以了。我就猜測s3cmci和sdhci-s3c就是對應不一樣的芯片。但是當我看了看代碼，不完全是這樣。
記得大神說過struct mmc_host。sd驅動用到的主要結構，但是sdhci-s3c用到的是struct sdhci_host。
這是什麼情況。
首先我就考慮sdhci到底是什麼，我看所有sdhci-*.c驅動都用到了sdhci.c，我看到sdhci.c對寄存器操作的偏移都
是一樣的，這樣我想到了usb的ochi驅動。應該有個sd控制器都遵循的協議。
然後我又打開了s3c6410的datasheet
第一行 SD Standard Host很耀眼。最後我在百度找的了這個：
Part_A2_SD_Host_Controller_Simplified_Specification_Ver2.00.pdf
這個就是所說的協議，sdhci.c要實現的東西。s3c2440並不遵循這個。
先看看sdhci吧，看c之前先看.h文件分析
/*
* linux/include/linux/mmc/sdhci.h - Secure Digital Host Controller Interface
*
* Copyright (C) 2005-2008 Pierre Ossman, All Rights Reserved.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or (at
* your option) any later version.
*/
#ifndef LINUX_MMC_SDHCI_H
#define LINUX_MMC_SDHCI_H
#include <linux/scatterlist.h>
#include <linux/compiler.h>
#include <linux/types.h>
#include <linux/io.h>
#include <linux/mmc/host.h>
struct sdhci_host {
/* Data set by hardware interface driver */
const char *hw_name; /* Hardware bus name */ //硬件總線名
unsigned int quirks; /* Deviations from spec. */ //偏離規範
//我們看有哪些怪癖，還有代碼會如何處理
/* Controller doesn't honor resets unless we touch the clock register */
#define SDHCI_QUIRK_CLOCK_BEFORE_RESET (1<<0)
/*
SDHCI_QUIRK_CLOCK_BEFORE_RESET 是有的要在復位前設置時鐘寄存器
會在復位前調用host->ops->set_clock(host, clock);驅動提供
*/
/* Controller has bad caps bits, but really supports DMA */
#define SDHCI_QUIRK_FORCE_DMA (1<<1)
/*
if (host->quirks & SDHCI_QUIRK_FORCE_DMA)
host->flags |= SDHCI_USE_SDMA;
就是支持SDMA
*/
/* Controller doesn't like to be reset when there is no card inserted. */
#define SDHCI_QUIRK_NO_CARD_NO_RESET (1<<2)
/*
上面英文已說的很清楚：
沒有卡插入時，控制器不想復位。
在復位時遇到這個標準，會想嘗試讀當前的狀態，成功返回，失敗進行復位。
*/
/* Controller doesn't like clearing the power reg before a change */
#define SDHCI_QUIRK_SINGLE_POWER_WRITE (1<<3)
/*
控制器不想清除電源寄存器在一個改變MMC_VDD前。
遇到這個，直接改電源寄存器值，不清除。
*/
/* Controller has flaky internal state so reset it on each ios change */
#define SDHCI_QUIRK_RESET_CMD_DATA_ON_IOS (1<<4)
/*
在sdhci_do_set_ios()中會用到。
解釋：
有些控制器在一些操作時會發瘋，即使是CMD0,解決方法就是復位每一個ios.
*/
/* Controller has an unusable DMA engine */
#define SDHCI_QUIRK_BROKEN_DMA (1<<5)
//控制器有一個無法使用的DMA引擎
//SDMA: secure DMA
//ADMA: advanced DMA
/* Controller has an unusable ADMA engine */
#define SDHCI_QUIRK_BROKEN_ADMA (1<<6)
//控制器有一個無法使用的ADMA引擎
/* Controller can only DMA from 32-bit aligned addresses */
#define SDHCI_QUIRK_32BIT_DMA_ADDR (1<<7)
//DMA要32位地址對齊
/* Controller can only DMA chunk sizes that are a multiple of 32 bits */
#define SDHCI_QUIRK_32BIT_DMA_SIZE (1<<8)
//DMA的大小是32的倍數
/* Controller can only ADMA chunks that are a multiple of 32 bits */
#define SDHCI_QUIRK_32BIT_ADMA_SIZE (1<<9)
//ADMA的大小是32的倍數
//遇到這些地址和大小限制，會先判斷數據。
/* Controller needs to be reset after each request to stay stable */
#define SDHCI_QUIRK_RESET_AFTER_REQUEST (1<<10)
//每個請求之後控制器需要復位來保持穩定
/*
在sdhci_tasklet_finish()中，即任務完成時，
當host->quirks & SDHCI_QUIRK_RESET_AFTER_REQUEST成立時，
執行復位。
*/
/* Controller needs voltage and power writes to happen separately */
#define SDHCI_QUIRK_NO_SIMULT_VDD_AND_POWER (1<<11)
/*
這個標準是開啓電源時，要先設置電壓。
Marvell CaFe的芯片就是如此
代碼，先設置，再或上SDHCI_POWER_ON開啓
if (host->quirks & SDHCI_QUIRK_NO_SIMULT_VDD_AND_POWER)
sdhci_writeb(host, pwr, SDHCI_POWER_CONTROL);
pwr |= SDHCI_POWER_ON;
sdhci_writeb(host, pwr, SDHCI_POWER_CONTROL);
*/
/* Controller provides an incorrect timeout value for transfers */
#define SDHCI_QUIRK_BROKEN_TIMEOUT_VAL (1<<12)
//控制器提供一個不正確的超時值。
/*
會用0xE作爲timeout.就是讓硬件有個長的超時值，比短的好。
if (host->quirks & SDHCI_QUIRK_BROKEN_TIMEOUT_VAL)
return 0xE;
*/
/* Controller has an issue with buffer bits for small transfers */
#define SDHCI_QUIRK_BROKEN_SMALL_PIO (1<<13)
//控制器支持小字節傳輸
//有些控制器（例如：JMicron JMB38x)弄亂傳輸位，（小於4字節）。
//只要它有一個block,我們可以忽略這些位。
//寄存器PRNSTS(s3c6410有這個寄存器)的第11位(buffer read enable)會被忽略
/* Controller does not provide transfer-complete interrupt when not busy */
#define SDHCI_QUIRK_NO_BUSY_IRQ (1<<14)
//當忙的時候，控制器不提供傳輸完成中斷
//如果忙的話，linux會執行下面的代碼
/*
if (intmask & SDHCI_INT_RESPONSE)
sdhci_finish_command(host);
*/
/* Controller has unreliable card detection */
#define SDHCI_QUIRK_BROKEN_CARD_DETECTION (1<<15)
//不可靠的卡檢測
/*
sdhci_set_card_detection()函數會判斷返回：
if (host->quirks & SDHCI_QUIRK_BROKEN_CARD_DETECTION)
return;
*/
/* Controller reports inverted write-protect state */
#define SDHCI_QUIRK_INVERTED_WRITE_PROTECT (1<<16)
/*
報告反的寫保護狀態值：
sdhci_check_ro()函數：
return host->quirks & SDHCI_QUIRK_INVERTED_WRITE_PROTECT ?
!is_readonly : is_readonly;
*/
/* Controller has nonstandard clock management */
#define SDHCI_QUIRK_NONSTANDARD_CLOCK (1<<17)
//非標準時鐘管理
//不標準，你就自己搞吧
/*
sdhci_set_clock()
if (host->ops->set_clock) {
host->ops->set_clock(host, clock);
if (host->quirks & SDHCI_QUIRK_NONSTANDARD_CLOCK)
return;
}
*/
/* Controller does not like fast PIO transfers */
#define SDHCI_QUIRK_PIO_NEEDS_DELAY (1<<18)
//pio需要延時
//要延時就給他延時
/*
sdhci_transfer_pio()中
if (host->quirks & SDHCI_QUIRK_PIO_NEEDS_DELAY)
udelay(100);
*/
/* Controller losing signal/interrupt enable states after reset */
#define SDHCI_QUIRK_RESTORE_IRQS_AFTER_RESET (1<<19)
//復位後會丟掉信號/中斷使能狀態
/*
在sdhci_reset()中，
先讀出中斷使能狀態
if (host->quirks & SDHCI_QUIRK_RESTORE_IRQS_AFTER_RESET)
ier = sdhci_readl(host, SDHCI_INT_ENABLE);
復位完再設置一下
if (host->quirks & SDHCI_QUIRK_RESTORE_IRQS_AFTER_RESET)
sdhci_clear_set_irqs(host, SDHCI_INT_ALL_MASK, ier);
*/
/* Controller has to be forced to use block size of 2048 bytes */
#define SDHCI_QUIRK_FORCE_BLK_SZ_2048 (1<<20)
//控制器被迫使用2048字節的塊大小
/*
if (host->quirks & SDHCI_QUIRK_FORCE_BLK_SZ_2048) {
mmc->max_blk_size = 2;
*/
/* Controller cannot do multi-block transfers */
#define SDHCI_QUIRK_NO_MULTIBLOCK (1<<21)
//不能多塊處理
/*
sdhci_add_host()中
//Maximum block count.
mmc->max_blk_count = (host->quirks & SDHCI_QUIRK_NO_MULTIBLOCK) ? 1 : 65535;
可以看一下spec,有三種：
Single Block, Multi Block, Infinite Block.
*/
/* Controller can only handle 1-bit data transfers */
#define SDHCI_QUIRK_FORCE_1_BIT_DATA (1<<22)
//一位數據傳輸
//不是1位就4位
/*
if (!(host->quirks & SDHCI_QUIRK_FORCE_1_BIT_DATA))
mmc->caps |= MMC_CAP_4_BIT_DATA;
在這段代碼之前有一句：
一個控制器可以支持8位寬度，但板子本身可能沒有引腳引出。
板支持8位寬度必須在自己的平臺代碼調用sdhci_add_host()之
前,設置“MMC->caps |= MMC_CAP_8_BIT_DATA;”
對於8-bits不是同一的代碼處理
通過sdhci_ops的platform_8bit_width(函數指針)自己處理。
*/
/* Controller needs 10ms delay between applying power and clock */
#define SDHCI_QUIRK_DELAY_AFTER_POWER (1<<23)
//設置電源和時鐘之間要10ms延時
/*
sdhci_set_power()
if (host->quirks & SDHCI_QUIRK_DELAY_AFTER_POWER)
mdelay(10);
*/
/* Controller uses SDCLK instead of TMCLK for data timeouts */
#define SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK (1<<24)
//用SDCLK代替TMCLK作爲數據超時
//SDCLK是sd總線時鐘
//TMCLK是專門爲了檢測超時的時鐘
/* Controller reports wrong base clock capability */
#define SDHCI_QUIRK_CAP_CLOCK_BASE_BROKEN (1<<25)
//基本時鐘功能報錯
/*
if (host->max_clk == 0 || host->quirks &
SDHCI_QUIRK_CAP_CLOCK_BASE_BROKEN) {
if (!host->ops->get_max_clock) {
pr_err("%s: Hardware doesn't specify base clock "
"frequency.\n", mmc_hostname(mmc));
return -ENODEV;
}
host->max_clk = host->ops->get_max_clock(host);
}
可以看出max_clk爲0時，我們可以通過host->ops->get_max_clock()獲得
*/
/* Controller cannot support End Attribute in NOP ADMA descriptor */
#define SDHCI_QUIRK_NO_ENDATTR_IN_NOPDESC (1<<26)
//不支持NOP ADMA屬性
/*
在sdhci_adma_table_pre()中
如果有此標誌就不調用
// nop, end, valid
sdhci_set_adma_desc(desc, 0, 0, 0x3);
*/
/* Controller is missing device caps. Use caps provided by host */
#define SDHCI_QUIRK_MISSING_CAPS (1<<27)
//缺少設備caps，使用主機的caps
/*
sdhci_add_host()
caps[0] = (host->quirks & SDHCI_QUIRK_MISSING_CAPS) ? host->caps :
sdhci_readl(host, SDHCI_CAPABILITIES);
*/
/* Controller uses Auto CMD12 command to stop the transfer */
#define SDHCI_QUIRK_MULTIBLOCK_READ_ACMD12 (1<<28)
//spec中說的Auto CMD12(停止命令)
/*
最終會通過mode寫到寄存裏
sdhci_writew(host, mode, SDHCI_TRANSFER_MODE);
*/
/* Controller doesn't have HISPD bit field in HI-SPEED SD card */
#define SDHCI_QUIRK_NO_HISPD_BIT (1<<29)
//沒有HISPD位
//這個會通過ctrl寫入
/*
sdhci_writeb(host, ctrl, SDHCI_HOST_CONTROL);
*/
/* Controller treats ADMA descriptors with length 0000h incorrectly */
#define SDHCI_QUIRK_BROKEN_ADMA_ZEROLEN_DESC (1<<30)
//長度爲0的ADAM描述符認爲不正確
/*
if (host->quirks & SDHCI_QUIRK_BROKEN_ADMA_ZEROLEN_DESC)
mmc->max_seg_size = 65535;
else
mmc->max_seg_size = 65536;
這個max_seg_size是做分散/聚合是每個條目不能大於64k
*/
/* The read-only detection via SDHCI_PRESENT_STATE register is unstable */
#define SDHCI_QUIRK_UNSTABLE_RO_DETECT (1<<31)
//通過PRESENT_STATE寄存器檢測read-only是不準的
//如果這樣就多次檢測
/*
ro_count = 0;
for (i = 0; i < SAMPLE_COUNT; i++) {
if (sdhci_check_ro(host)) {
if (++ro_count > SAMPLE_COUNT / 2)
return 1;
}
msleep(30);
}
*/
unsigned int quirks2; /* More deviations from spec. */
#define SDHCI_QUIRK2_OWN_CARD_DETECTION (1<<0)
//自己的卡檢測
/*
和上面的SDHCI_QUIRK_BROKEN_CARD_DETECTION一樣
*/
int irq; /* Device IRQ */
void __iomem *ioaddr; /* Mapped address */
const struct sdhci_ops *ops; /* Low level hw interface */
/*
主要是硬件操作接口
struct sdhci_ops {
#ifdef CONFIG_MMC_SDHCI_IO_ACCESSORS
u32 (*read_l)(struct sdhci_host *host, int reg);
u16 (*read_w)(struct sdhci_host *host, int reg);
u8 (*read_b)(struct sdhci_host *host, int reg);
void (*write_l)(struct sdhci_host *host, u32 val, int reg);
void (*write_w)(struct sdhci_host *host, u16 val, int reg);
void (*write_b)(struct sdhci_host *host, u8 val, int reg);
#endif
上面你不設置就使用內核提供的readl等
void (*set_clock)(struct sdhci_host *host, unsigned int clock);//設置時鐘
int (*enable_dma)(struct sdhci_host *host);//使能dma
unsigned int (*get_max_clock)(struct sdhci_host *host);//獲取最大時鐘
unsigned int (*get_min_clock)(struct sdhci_host *host);//獲取最小時鐘
unsigned int (*get_timeout_clock)(struct sdhci_host *host);//獲得超時時鐘
int (*platform_8bit_width)(struct sdhci_host *host,
int width);//八位傳輸操作
void (*platform_send_init_74_clocks)(struct sdhci_host *host,
u8 power_mode);//只在sdhci-pxav3.c看到使用，不清楚幹嘛
unsigned int (*get_ro)(struct sdhci_host *host);//獲取readonly狀態
void (*platform_reset_enter)(struct sdhci_host *host, u8 mask);//復位之前處理
void (*platform_reset_exit)(struct sdhci_host *host, u8 mask);//復位之後處理
int (*set_uhs_signaling)(struct sdhci_host *host, unsigned int uhs);//uhs:Ultra High Speed 設置超高速信號
void (*hw_reset)(struct sdhci_host *host);//復位
};
*/
struct regulator *vmmc; /* Power regulator *///電源調節器
/* Internal data */
struct mmc_host *mmc; /* MMC structure */ //大名鼎鼎的mmc結構
u64 dma_mask; /* custom DMA mask */
#if defined(CONFIG_LEDS_CLASS) || defined(CONFIG_LEDS_CLASS_MODULE)
struct led_classdev led; /* LED control */
char led_name[32];
#endif
spinlock_t lock; /* Mutex */
int flags; /* Host attributes */
#define SDHCI_USE_SDMA (1<<0) /* Host is SDMA capable */
#define SDHCI_USE_ADMA (1<<1) /* Host is ADMA capable */
#define SDHCI_REQ_USE_DMA (1<<2) /* Use DMA for this req. */
#define SDHCI_DEVICE_DEAD (1<<3) /* Device unresponsive */
#define SDHCI_SDR50_NEEDS_TUNING (1<<4) /* SDR50 needs tuning */
#define SDHCI_NEEDS_RETUNING (1<<5) /* Host needs retuning */
#define SDHCI_AUTO_CMD12 (1<<6) /* Auto CMD12 support */
#define SDHCI_AUTO_CMD23 (1<<7) /* Auto CMD23 support */
#define SDHCI_PV_ENABLED (1<<8) /* Preset value enabled */
#define SDHCI_SDIO_IRQ_ENABLED (1<<9) /* SDIO irq enabled */
unsigned int version; /* SDHCI spec. version *///版本,目前是1.0 2.0 3.0
unsigned int max_clk; /* Max possible freq (MHz) */
unsigned int timeout_clk; /* Timeout freq (KHz) */
unsigned int clk_mul; /* Clock Muliplier value */
unsigned int clock; /* Current clock (MHz) */
u8 pwr; /* Current voltage */
bool runtime_suspended; /* Host is runtime suspended */ //掛起標誌
struct mmc_request *mrq; /* Current request */
struct mmc_command *cmd; /* Current command */
struct mmc_data *data; /* Current data request */
unsigned int data_early:1; /* Data finished before cmd *///數據管理完成在命令完成之前
struct sg_mapping_iter sg_miter; /* SG state for PIO *///sg 狀態
unsigned int blocks; /* remaining PIO blocks */ //剩餘PIO的blocks
int sg_count; /* Mapped sg entries *///映射的SG項數目
u8 *adma_desc; /* ADMA descriptor table */ //AMDA描述符表
u8 *align_buffer; /* Bounce buffer */ //反彈緩衝
dma_addr_t adma_addr; /* Mapped ADMA descr. table */
dma_addr_t align_addr; /* Mapped bounce buffer */
struct tasklet_struct card_tasklet; /* Tasklet structures */
/*
中斷函數中：
if (intmask & (SDHCI_INT_CARD_INSERT | SDHCI_INT_CARD_REMOVE))
會調用tasklet_schedule(&host->card_tasklet);
可以看出是處理card insert和remove，對應的函數是 sdhci_tasklet_card()
*/
struct tasklet_struct finish_tasklet;
/*
sdhci_remove_host()函數，如果host->mrq不爲NULL。
就會調用tasklet_schedule(&host->finish_tasklet);
可以看出是有請求時sd被remove會執行的處理，對應的函數sdhci_tasklet_finish()；
*/
struct timer_list timer; /* Timer for timeouts *///超時定時器
unsigned int caps; /* Alternative capabilities *///另類功能
unsigned int ocr_avail_sdio; /* OCR bit masks */ //ocr 寄存器記錄着支持的電壓
unsigned int ocr_avail_sd;
unsigned int ocr_avail_mmc;
//CMD19在SD spec中是預留的。在SDHCI v3.00中有個tuning command會用到
wait_queue_head_t buf_ready_int; /* Waitqueue for Buffer Read Ready interrupt */
/*
在 sdhci_data_irq()
// CMD19 generates _only_ Buffer Read Ready interrupt
if (intmask & SDHCI_INT_DATA_AVAIL) {
if (SDHCI_GET_CMD(sdhci_readw(host, SDHCI_COMMAND)) ==
MMC_SEND_TUNING_BLOCK) {
host->tuning_done = 1;
wake_up(&host->buf_ready_int);
return;
}
}
喚醒的函數是sdhci_execute_tuning()
*/
unsigned int tuning_done; /* Condition flag set when CMD19 succeeds *///CMD19成功標誌
unsigned int tuning_count; /* Timer count for re-tuning *///tuning計時
unsigned int tuning_mode; /* Re-tuning mode supported by host *///tuning模式支持
#define SDHCI_TUNING_MODE_1 0
struct timer_list tuning_timer; /* Timer for tuning *///tuning用的定時器
unsigned long private[0] ____cacheline_aligned;
};
#endif /* LINUX_MMC_SDHCI_H */