From:http://cid-b6be8a6f2ed519d0.spaces.live.com/blog/cns!B6BE8A6F2ED519D0!114.entry
//*******************************************************
//* 2007.6.18
//*******************************************************
在/kernel/include/asm-arm/arch-s3c2410/bitfield.h 文件中：
#ifndef __ASSEMBLY__
#define UData(Data) ((unsigned long) (Data))
#else
#define UData(Data) (Data)
#endif
例：UData(5); = 5
/*
* MACRO: Fld
*
* Purpose
* The macro "Fld" encodes a bit field, given its size and its shift value
* with respect to bit 0.
*
* Note
* A more intuitive way to encode bit fields would have been to use their
* mask. However, extracting size and shift value information from a bit
* field's mask is cumbersome and might break the assembler (255-character
* line-size limit).
*
* Input
* Size Size of the bit field, in number of bits.
* Shft Shift value of the bit field with respect to bit 0.
*
* Output
* Fld Encoded bit field.
*/
#define Fld(Size, Shft) (((Size) << 16) + (Shft))
例：Fld(2,5); = 0x20005
/*
* MACROS: FSize, FShft, FMsk, FAlnMsk, F1stBit
*
* Purpose
* The macros "FSize", "FShft", "FMsk", "FAlnMsk", and "F1stBit" return
* the size, shift value, mask, aligned mask, and first bit of a
* bit field.
*
* Input
* Field Encoded bit field (using the macro "Fld").
*
* Output
* FSize Size of the bit field, in number of bits.
* FShft Shift value of the bit field with respect to bit 0.
* FMsk Mask for the bit field.
* FAlnMsk Mask for the bit field, aligned on bit 0.
* F1stBit First bit of the bit field.
*/
#define FSize(Field) ((Field) >> 16)
例：FSize(0x20005); = 2
#define FShft(Field) ((Field) & 0x0000FFFF)
例：FShft(0x20005); = 5
/*
* MACRO: FInsrt
*
* Purpose
* The macro "FInsrt" inserts a value into a bit field by shifting the
* former appropriately.
*
* Input
* Value Bit-field value.
* Field Encoded bit field (using the macro "Fld").
*
* Output
* FInsrt Bit-field value positioned appropriately.
*/
#define FInsrt(Value, Field) \
(UData (Value) << FShft (Field))
例：FInsrt(0x3, 0x20005); = 0x3 << 0x0005 = 0x60
------------------------------------------------------------------------
在/kernel/include/asm-arm/arch-s3c2410/hardware.h 文件中：
/*
* S3C2410 internal I/O mappings
*
* We have the following mapping:
* phys virt
* 48000000 e8000000
*/
#define VIO_BASE 0xe8000000 /* virtual start of IO space */
#define PIO_START 0x48000000 /* physical start of IO space */
#define io_p2v(x) ((x) | 0xa0000000)
#define io_v2p(x) ((x) & ~0xa0000000)
# define __REG(x) io_p2v(x)
# define __PREG(x) io_v2p(x)
這里，在實(shí)際的寄存器操作中，都用__REG(x) 宏將物理地址轉(zhuǎn)換為了虛擬地址，然后再對(duì)這些虛擬地址進(jìn)行讀寫(xiě)操作。
------------------------------------------------------------------------
當(dāng)應(yīng)用程序?qū)υO(shè)備文件進(jìn)行ioctl操作時(shí)候會(huì)調(diào)用它們。對(duì)于fb_get_fix()，應(yīng)用程序傳入的是fb_fix_screeninfo結(jié)構(gòu)，在函數(shù)中對(duì)其成員變量賦值，主要是smem_start（緩沖區(qū)起始地址）和smem_len（緩沖區(qū)長(zhǎng)度），最終返回給應(yīng)用程序。
在/kernel/drivers/video/s3c2410fb.c 文件中的s3c2410fb_map_video_memory 函數(shù)中：
fbi->fb.fix.smem_len = fbi->max_xres * fbi->max_yres *
fbi->max_bpp / 8;
fbi->map_size = PAGE_ALIGN(fbi->fb.fix.smem_len + PAGE_SIZE);
fbi->map_cpu = consistent_alloc(GFP_KERNEL, fbi->map_size,
&fbi->map_dma);
if (fbi->map_cpu)
{
fbi->screen_cpu = fbi->map_cpu + PAGE_SIZE;
fbi->screen_dma = fbi->map_dma + PAGE_SIZE;
fbi->fb.fix.smem_start = fbi->screen_dma;
}
在/kernel/include/asm-arm/proc-armo/page.h 文件中：
/* PAGE_SHIFT determines the page size. This is configurable. */
#if defined(CONFIG_PAGESIZE_16)
#define PAGE_SHIFT 14 /* 16K */
#else /* default */
#define PAGE_SHIFT 15 /* 32K */
#endif
在/kernel/include/asm-arm/page.h 文件中：
#define PAGE_SIZE (1UL << PAGE_SHIFT)
#define PAGE_MASK (~(PAGE_SIZE-1))
/* to align the pointer to the (next) page boundary */
#define PAGE_ALIGN(addr) (((addr)+PAGE_SIZE-1)&PAGE_MASK)
在/kernel/arch/arm/mm/consistent.c 文件中：
/*
* This allocates one page of cache-coherent memory space and returns
* both the virtual and a "dma" address to that space. It is not clear
* whether this could be called from an interrupt context or not. For
* now, we expressly forbid it, especially as some of the stuff we do
* here is not interrupt context safe.
*
* Note that this does *not* zero the allocated area!
*/
void *consistent_alloc(int gfp, size_t size, dma_addr_t *dma_handle)
這里首先計(jì)算出需要視頻緩沖區(qū)的大?。↙CD屏的寬度 * LCD屏的高度 * 每像素的位數(shù) / 每字節(jié)的位數(shù)）
fbi->fb.fix.smem_len = 240*320*16/8 = 0x25800 =150K（9.375個(gè)PAGE）
PAGE_SHIFT = 14
PAGE_SIZE = 1<<14 = 0x4000 = 16K （1個(gè)PAGE）
PAGE_MASK = 0xFFFFC000
fbi->map_size = PAGE_ALIGN(fbi->fb.fix.smem_len + PAGE_SIZE) = PAGE_ALIGN(150K + 16K) = PAGE_ALIGN(166K)
= (166K + 16K - 1) & 0xFFFFC000 = 0x2D7FF & 0xFFFFC000 = 0x2C000 =176K
consistent_alloc(GFP_KERNEL, 176K, &fbi->map_dma);
最后得到：
framebuffer（物理地址）
|---------------|
| ... |
-------|---------------| <-- fbi->map_dma
| 16K |
分配了 |---------------| <-- fbi->screen_dma = fbi->fb.fix.smem_start
176K | |
共11個(gè) | | 160K = 10個(gè)PAGE
PAGE | 160K | 可以容下所需的150K 視頻緩沖區(qū)大小
(16K) | |
| |
-------|---------------|-------
| ... |
|---------------|
//*******************************************************
//* 2007.6.19
//*******************************************************
在/kernel/drivers/video/s3c2410fb.c 文件中的s3c2410fb_activate_var 函數(shù)中：
unsigned long VideoPhysicalTemp = fbi->screen_dma;
這里已經(jīng)得到了framebuffer 在內(nèi)存中的起始地址為VideoPhysicalTemp，地址數(shù)據(jù)位為A[30:0]。
new_regs.lcdcon1 = fbi->reg.lcdcon1 & ~LCD1_ENVID;
new_regs.lcdcon2 = (fbi->reg.lcdcon2 & ~LCD2_LINEVAL_MSK)
| LCD2_LINEVAL(var->yres - 1);
/* TFT LCD only ! */
new_regs.lcdcon3 = (fbi->reg.lcdcon3 & ~LCD3_HOZVAL_MSK)
| LCD3_HOZVAL(var->xres - 1);
new_regs.lcdcon4 = fbi->reg.lcdcon4;
new_regs.lcdcon5 = fbi->reg.lcdcon5;
LCDCON1 首先需要禁止視頻輸出才能進(jìn)行寄存器的設(shè)置，然后對(duì)LCDCON2，LCDCON3 進(jìn)行設(shè)置，主要是增加LINEVAL 和HOZVAL 這兩個(gè)顯示尺寸的參數(shù)。LCDCON4，LCDCON5 按原來(lái)配置設(shè)置。
LCDBANK[29:21] 為系統(tǒng)內(nèi)存中視頻緩沖區(qū)在系統(tǒng)存儲(chǔ)器內(nèi)的段地址的A[30:22]
LCDBASEU[20:0] 為L(zhǎng)CD framebuffer 的起始地址的A[21:1]
LCDBASEL[20:0] 為L(zhǎng)CD framebuffer 的結(jié)束地址的A[21:1]
OFFSIZE[21:11] 為某一行的第一個(gè)半字與前一行最后一個(gè)半字之間的距離（單位：半字?jǐn)?shù)，即2個(gè)字節(jié)）
PAGEWIDTH[10:0] 為顯示存儲(chǔ)區(qū)的可見(jiàn)幀寬度（單位：半字?jǐn)?shù)，即2個(gè)字節(jié)）
new_regs.lcdsaddr1 =
LCDADDR_BANK(((unsigned long)VideoPhysicalTemp >> 22))
| LCDADDR_BASEU(((unsigned long)VideoPhysicalTemp >> 1));
new_regs.lcdsaddr2 = LCDADDR_BASEL(
((unsigned long)VideoPhysicalTemp + (var->xres * 2 * (var>yres))) >> 1);
這里L(fēng)CDADDR_BASEL 的計(jì)算方法為用framebuffer 在內(nèi)存中的起始地址VideoPhysicalTemp，加上framebuffer 的大小（LCD屏的寬度 * LCD屏的高度 * 每像素的位數(shù) / 每字節(jié)的位數(shù)），得到framebuffer 在內(nèi)存中的結(jié)束地址，然后右移1位。
new_regs.lcdsaddr3 = LCDADDR_OFFSET(0) | (LCDADDR_PAGE(var->xres));
這里PAGEWIDTH 的計(jì)算方法為：LCD屏的寬度*每像素的位數(shù)/16位 （半字）。
問(wèn)題：以上這些操作是否已經(jīng)對(duì)DMA 控制器進(jìn)行了設(shè)置？
我認(rèn)為這里將framebuffer 在內(nèi)存中的起始地址為VideoPhysicalTemp 變換后載入LCDADDR1，LCDADDR2，LCDADDR3 中就已經(jīng)完成了對(duì)LCDCDMA 控制器的源數(shù)據(jù)的基地址設(shè)置，當(dāng)打開(kāi)LCDCON1 |= LCD1_ENVID; 后就可以由LCDCDMA 控制器自動(dòng)從framebuffer 中傳數(shù)據(jù)到LCD 屏幕了。
------------------------------------------------------------------------
在/kernel/drivers/video/s3c2410fb.c 文件中的xxx_stn_info 結(jié)構(gòu)體初始化中：
lcdcon5 : LCD5_FRM565 | LCD5_INVVLINE | LCD5_INVVFRAME | LCD5_HWSWP | LCD5_PWREN,
INVVCLK ， INVLINE ， INVFRAME ， INVVD ：通過(guò)前面的時(shí)序圖，我們知道，CPU的LCD控制器輸出的時(shí)序默認(rèn)是正脈沖，而LCD需要VSYNC（VFRAME）、VLINE（HSYNC）均為負(fù)脈沖，因此 INVLINE 和 INVFRAME 必須設(shè)為“1 ”，即選擇反相輸出。 INVVDEN ， INVPWREN ， INVLEND 的功能同前面的類似。
PWREN 為L(zhǎng)CD電源使能控制。在CPU LCD控制器的輸出信號(hào)中，有一個(gè)電源使能管腳LCD_PWREN，用來(lái)做為L(zhǎng)CD屏電源的開(kāi)關(guān)信號(hào)。
其中LCD5_HWSWP 一項(xiàng)，設(shè)置了LCD從內(nèi)存中顯示數(shù)據(jù)時(shí)，經(jīng)過(guò)了半字交換。
16BPP Display
(BSWP = 0, HWSWP = 0)
D[31:16] D[15:0]
000H P1 P2
004H P3 P4
008H P5 P6
...
(BSWP = 0, HWSWP = 1)
D[31:16] D[15:0]
000H P2 P1
004H P4 P3
008H P6 P5
...
像素顯示順序如下：
P1 P2 P3 P4 P5 ...
例如：內(nèi)存地址的數(shù)據(jù)為：0x11223344 （32位）
系統(tǒng)存儲(chǔ)器采用Big-Endian（大端模式）存儲(chǔ)格式，地址數(shù)據(jù)格式如下：
D[31:16] D[15:0]
00 01 02 03
00H 0x11 0x22 0x33 0x44
(0x1122) (0x3344)
04H ...
08H ...
則首先顯示0x3344 的數(shù)據(jù)到第一個(gè)像素，然后再顯示0x1122 到第二個(gè)像素。
系統(tǒng)存儲(chǔ)器采用Little-Endian（小端模式）存儲(chǔ)格式，地址數(shù)據(jù)格式如下：
D[31:16] D[15:0]
03 02 01 00
00H 0x11 0x22 0x33 0x44
(0x1122) (0x3344)
04H ...
08H ...
則首先顯示0x3344 的數(shù)據(jù)到第一個(gè)像素，然后再顯示0x1122 到第二個(gè)像素。
//*******************************************************
//* 2007.6.20
//*******************************************************
在/kernel/arch/arm/mm/consistent.c 文件中的consistent_alloc 函數(shù)中：
void *consistent_alloc(int gfp, size_t size, dma_addr_t *dma_handle)
{
...
virt = page_address(page);
*dma_handle = virt_to_bus(virt);
ret = __ioremap(virt_to_phys(virt), size, 0);
...
}
這里調(diào)用該函數(shù)來(lái)分配一段內(nèi)存空間有兩個(gè)返回值，一個(gè)返回值返回給了ret 指針，另一個(gè)返回值返回給了dma_handle 指針。virt_to_bus 和virt_to_phys 函數(shù)的調(diào)用可以參考下面的分析。經(jīng)過(guò)分析這兩個(gè)函數(shù)作用一樣，都是將virt 這個(gè)虛擬地址轉(zhuǎn)換為物理地址。所以返回給指針dma_handle 的是所分配內(nèi)存的起始地址（物理地址）。__ioremap 函數(shù)的調(diào)用也可以參考下面的說(shuō)明，該函數(shù)也返回所分配內(nèi)存的起始地址（虛擬地址），不過(guò)是經(jīng)過(guò)I/O 內(nèi)存映射的，把物理地址轉(zhuǎn)換為了虛擬地址。
這樣一來(lái)就很清楚了，返回的framebuffer 的物理地址給了指針dma_handle，也就是fbi->map_dma，到fbi->screen_dma，再到fbi->fb.fix.smem_start，最后到了指針VideoPhysicalTemp，這樣寫(xiě)入到LCDADDR1，LCDADDR2 寄存器中的framebuffer 的地址其實(shí)都是物理地址。
而返回的framebuffer 的虛擬地址給了指針ret，也就是fbi->map_cpu，到fbi->screen_cpu，最后到了display->screen_base（見(jiàn)/kernel/drivers/video/s3c2410fb.c 文件中的s3c2410fb_set_var 函數(shù)）。
------------------------------------------------------------------------
在/kernel/drivers/video/fbmem.c 文件中：
/**
* register_framebuffer - registers a frame buffer device
* @fb_info: frame buffer info structure
*
* Registers a frame buffer device @fb_info.
*
* Returns negative errno on error, or zero for success.
*
*/
int
register_framebuffer(struct fb_info *fb_info)
/**
* unregister_framebuffer - releases a frame buffer device
* @fb_info: frame buffer info structure
*
* Unregisters a frame buffer device @fb_info.
*
* Returns negative errno on error, or zero for success.
*
*/
int
unregister_framebuffer(struct fb_info *fb_info)
static int
fb_open(struct inode *inode, struct file *file)
static int
fb_release(struct inode *inode, struct file *file)
static ssize_t
fb_read(struct file *file, char *buf, size_t count, loff_t *ppos)
static ssize_t
fb_write(struct file *file, const char *buf, size_t count, loff_t *ppos)
static int
fb_ioctl(struct inode *inode, struct file *file, unsigned int cmd,
unsigned long arg)
static int
fb_mmap(struct file *file, struct vm_area_struct * vma)
在該文件中包含了所有驅(qū)動(dòng)LCD 的函數(shù)。在fb_read 和fb_write 這兩個(gè)函數(shù)中，都對(duì)framebuffer 進(jìn)行了操作。
fb_read 函數(shù)中：
char *base_addr;
base_addr = info->disp->screen_base;
count -= copy_to_user(buf, base_addr+p, count);
fb_write 函數(shù)中：
char *base_addr;
base_addr = info->disp->screen_base;
count -= copy_from_user(base_addr+p, buf, count);
所讀寫(xiě)的framebuffer 的基地址就是disp->screen_base，也就是fbi->screen_cpu 所指的framebuffer 的虛擬地址。
從而得到：
framebuffer（虛擬地址）
|---------------|
| ... |
-------|---------------| <-- fbi->map_cpu
| 16K |
分配了 |---------------| <-- fbi->screen_cpu = display->screen_base
176K | |
共11個(gè) | | 160K = 10個(gè)PAGE
PAGE | 160K | 可以容下所需的150K 視頻緩沖區(qū)大小
(16K) | |
| |
-------|---------------|-------
| ... |
|---------------|
其中display->screen_base 結(jié)構(gòu)在/kernel/include/video/fbcon.h 文件中定義。
得出結(jié)論，在分配framebuffer 時(shí)一共返回兩個(gè)指針，雖然是同一塊內(nèi)存空間，但一個(gè)返回的是實(shí)際的物理地址，另一個(gè)返回的是經(jīng)過(guò)地址轉(zhuǎn)換的虛擬地址。在設(shè)置LCD 控制器中framebuffer 起始地址寄存器時(shí)，用的是所分配內(nèi)存的物理地址；而當(dāng)要對(duì)framebuffer 進(jìn)行讀寫(xiě)操作時(shí)，用的是同一塊內(nèi)存的物理地址所轉(zhuǎn)換后的虛擬地址。由此可以知道，內(nèi)核在對(duì)每個(gè)I/O 地址進(jìn)行讀寫(xiě)操作時(shí)用的都是經(jīng)過(guò)轉(zhuǎn)換的虛擬地址。
------------------------------------------------------------------------
------------------------------------------------------------------------
在/kernel/include/asm-arm/arch-s3c2410/memory.h 文件中：
/*
* Page offset: 3GB
*/
#define PAGE_OFFSET (0xc0000000UL)
#define PHYS_OFFSET (0x30000000UL)
/*
* We take advantage of the fact that physical and virtual address can be the
* saem. Thu NUMA code is handling the large holes that might exist between
* all memory banks.
*/
#define __virt_to_phys__is_a_macro
#define __phys_to_virt__is_a_macro
#define __virt_to_phys(x) ((x) - PAGE_OFFSET + PHYS_OFFSET)
#define __phys_to_virt(x) ((x) - PHYS_OFFSET + PAGE_OFFSET)
由此可見(jiàn)： 起始點(diǎn)地址 PHYS_OFFSET PAGE_OFFSET
| |
|--0x30000000--|------間隔------|
PHYS_OFFSET（物理地址起始點(diǎn)）： |--------------|...........................
|
|-----------0xc0000000----------|
PAGE_OFFSET（虛擬地址起始點(diǎn)）： |-------------------------------|..........
物理地址與虛擬地址的間隔為：PAGE_OFFSET - PHYS_OFFSET。這樣一來(lái)，以上對(duì)物理地址和虛擬地址之間轉(zhuǎn)換的宏定義就很好理解了。
虛擬地址轉(zhuǎn)為物理地址宏：__virt_to_phys(x)
= (x) - (PAGE_OFFSET - PHYS_OFFSET) = (x) - PAGE_OFFSET + PHYS_OFFSET
物理地址轉(zhuǎn)為虛擬地址宏：__phys_to_virt(x)
= (x) + (PAGE_OFFSET - PHYS_OFFSET) = (x) + PAGE_OFFSET - PHYS_OFFSET
內(nèi)核虛擬地址和實(shí)際物理地址僅僅是相差一個(gè)偏移量（PAGE_OFFSET），可以很方便的將其轉(zhuǎn)化為物理內(nèi)存地址，同時(shí)內(nèi)核也提供了virt_to_phys() 函數(shù)將內(nèi)核虛擬空間中的物理影射區(qū)地址轉(zhuǎn)化為物理地址。
/*
* Virtual view <-> DMA view memory address translations
* virt_to_bus: Used to translate the virtual address to an
* address suitable to be passed to set_dma_addr
* bus_to_virt: Used to convert an address for DMA operations
* to an address that the kernel can use.
*/
#define __virt_to_bus__is_a_macro
#define __bus_to_virt__is_a_macro
#define __virt_to_bus(x) __virt_to_phys(x)
#define __bus_to_virt(x) __phys_to_virt(x)
這里注意：__virt_to_bus(x) 就等于__virt_to_phys(x)
------------------------------------------------------------------------
在/kernel/include/asm-arm/memory.h 文件中：
/*
* These are *only* valid on the kernel direct mapped RAM memory.
*/
static inline unsigned long virt_to_phys(volatile void *x)
{
return __virt_to_phys((unsigned long)(x));
}
/*
* Virtual <-> DMA view memory address translations
* Again, these are *only* valid on the kernel direct mapped RAM
* memory.
*/
#define virt_to_bus(x) (__virt_to_bus((unsigned long)(x)))
由上面的分析可知：virt_to_bus(x) 和virt_to_phys(volatile void *x) 這兩個(gè)函數(shù)調(diào)用的都是__virt_to_phys(x) 即((x) - PAGE_OFFSET + PHYS_OFFSET)。所以這兩個(gè)調(diào)用都是將虛擬地址轉(zhuǎn)換為了物理地址。
------------------------------------------------------------------------
在/kernel/arch/arm/mm/ioremap.c 文件中：
/*
* Remap an arbitrary physical address space into the kernel virtual
* address space. Needed when the kernel wants to access high addresses
* directly.
*
* NOTE! We need to allow non-page-aligned mappings too: we will obviously
* have to convert them into an offset in a page-aligned mapping, but the
* caller shouldn't need to know that small detail.
*
* 'flags' are the extra L_PTE_ flags that you want to specify for this
* mapping. See include/asm-arm/proc-armv/pgtable.h for more information.
*/
void * __ioremap(unsigned long phys_addr, size_t size, unsigned long flags)
ioremap 函數(shù)的作用是將physical address以及bus address映射為kernel的
virtual adrress。
ioremap 的作用是把I/O 內(nèi)存地址（物理地址）映射到虛擬地址空間，使用之前需要分配I/O 內(nèi)存區(qū)域。但是，ioremap 函數(shù)的內(nèi)部實(shí)現(xiàn)并不是簡(jiǎn)單的（(IO的物理地址)-0x10000000 +0xE4000000）。所以，得到的虛擬地址可能是不同的。
因?yàn)閘inux 用的是頁(yè)面映射機(jī)制，CPU 不能按物理地址來(lái)訪問(wèn)存儲(chǔ)空間，而必須使用虛擬地址，所以必須反向的從物理地址出發(fā)找到一片虛存空間并建立起映射。
//*******************************************************
//* 2007.6.22
//*******************************************************
在/kernel/drivers/video/fbmem.c 文件中：
static struct file_operations fb_fops = {
owner: THIS_MODULE,
read: fb_read,
write: fb_write,
ioctl: fb_ioctl,
mmap: fb_mmap,
open: fb_open,
release: fb_release,
#ifdef HAVE_ARCH_FB_UNMAPPED_AREA
get_unmapped_area: get_fb_unmapped_area,
#endif
};
這個(gè)結(jié)構(gòu)中定義了對(duì)LCD 所分配的framebuffer 進(jìn)行讀寫(xiě)操作，以及一些內(nèi)存映射之類的函數(shù)，這些源函數(shù)都在該文件中。
/**
* register_framebuffer - registers a frame buffer device
* @fb_info: frame buffer info structure
*
* Registers a frame buffer device @fb_info.
*
* Returns negative errno on error, or zero for success.
*
*/
int
register_framebuffer(struct fb_info *fb_info)
這個(gè)是對(duì)LCD 的framebuffer 設(shè)備進(jìn)行注冊(cè)時(shí)調(diào)用到的注冊(cè)函數(shù)，該函數(shù)在/kernel/drivers/video/s3c2410fb.c 文件的s3c2410fb_init 函數(shù)里的最后部分被調(diào)用。
fb_info->devfs_handle =
devfs_register (devfs_handle, name_buf, DEVFS_FL_DEFAULT,
FB_MAJOR, i, S_IFCHR | S_IRUGO | S_IWUGO,
&fb_fops, NULL);
在注冊(cè)函數(shù)的最后部分，將前面的fb_fops 結(jié)構(gòu)里的各個(gè)驅(qū)動(dòng)函數(shù)的入口點(diǎn)傳入到devfs_register()設(shè)備注冊(cè)函數(shù)中。
//*******************************************************
//* 2007.6.26
//*******************************************************
上面這個(gè)devfs_register 函數(shù)（原型在/kernel/fs/devfs/base.c 文件中）執(zhí)行前，在fbmem_init 函數(shù)中調(diào)用了函數(shù)：
devfs_handle = devfs_mk_dir (NULL, "fb", NULL);
在/kernel/fs/devfs/base.c 文件中：
/**
* devfs_mk_dir - Create a directory in the devfs namespace.
* @dir: The handle to the parent devfs directory entry. If this is %NULL the
* new name is relative to the root of the devfs.
* @name: The name of the entry.
* @info: An arbitrary pointer which will be associated with the entry.
*
* Use of this function is optional. The devfs_register() function
* will automatically create intermediate directories as needed. This function
* is provided for efficiency reasons, as it provides a handle to a directory.
* Returns a handle which may later be used in a call to devfs_unregister().
* On failure %NULL is returned.
*/
devfs_handle_t devfs_mk_dir (devfs_handle_t dir, const char *name, void *info)
這個(gè)devfs_mk_dir 函數(shù)會(huì)在設(shè)備文件系統(tǒng)中創(chuàng)建一個(gè)名為fb 的目錄，并返回一個(gè)帶有devfs 設(shè)備文件系統(tǒng)目錄結(jié)構(gòu)的數(shù)據(jù)結(jié)構(gòu)變量devfs_handle。然后把這個(gè)數(shù)據(jù)結(jié)構(gòu)作為下一步調(diào)用devfs_register 函數(shù)時(shí)的參數(shù)，該參數(shù)在調(diào)用設(shè)備文件系統(tǒng)注冊(cè)清除函數(shù)devfs_unregister 時(shí)也要作為參數(shù)傳入。
/**
* devfs_register - Register a device entry.
* @dir: The handle to the parent devfs directory entry. If this is %NULL the
* new name is relative to the root of the devfs.
* @name: The name of the entry.
* @flags: A set of bitwise-ORed flags (DEVFS_FL_*).
* @major: The major number. Not needed for regular files.
* @minor: The minor number. Not needed for regular files.
* @mode: The default file mode.
* @ops: The &file_operations or &block_device_operations structure.
* This must not be externally deallocated.
* @info: An arbitrary pointer which will be written to the @private_data
* field of the &file structure passed to the device driver. You can set
* this to whatever you like, and change it once the file is opened (the next
* file opened will not see this change).
*
* Returns a handle which may later be used in a call to devfs_unregister().
* On failure %NULL is returned.
*/
devfs_handle_t devfs_register (devfs_handle_t dir, const char *name,
unsigned int flags,
unsigned int major, unsigned int minor,
umode_t mode, void *ops, void *info)
函數(shù)devfs_register 是設(shè)備文件系統(tǒng)的主冊(cè)函數(shù)，會(huì)在剛才創(chuàng)建的目錄下再創(chuàng)建一個(gè)名為name 的設(shè)備文件節(jié)點(diǎn)。返回的devfs_handle_t 數(shù)據(jù)結(jié)構(gòu)變量會(huì)在調(diào)用設(shè)備文件系統(tǒng)注冊(cè)清除函數(shù)devfs_unregister 時(shí)作為參數(shù)傳入。
fb_info->devfs_handle =
devfs_register (devfs_handle, name_buf, DEVFS_FL_DEFAULT,
FB_MAJOR, i, S_IFCHR | S_IRUGO | S_IWUGO,
&fb_fops, NULL);
調(diào)用該函數(shù)后，會(huì)在剛才創(chuàng)建的fb 目錄下再創(chuàng)建一個(gè)名為0 （name_buf）的設(shè)備文件節(jié)點(diǎn)，并賦予相應(yīng)的權(quán)限，以及主次設(shè)備號(hào)和file_operations 結(jié)構(gòu)的函數(shù)入口。
這樣一來(lái)，Linux 設(shè)備文件的創(chuàng)建，刪除和目錄層次等都由各設(shè)備驅(qū)動(dòng)程序管理，再也不用手工創(chuàng)建設(shè)備文件節(jié)點(diǎn)了，再也不需要mknod 時(shí)查找對(duì)應(yīng)的主設(shè)備號(hào)了，也不用依靠復(fù)雜的腳本來(lái)管理設(shè)備文件了。
