一、概述
1.1 简介
本文档主要包括LCD模块的驱动流程分析、Framebuffer相关知识、Gralloc等相关内容，以及LCD调试的一些经验和相关bug的分析和讲解。
1.2 开发环境
Android:4.1.2
Ubuntu:需要 10.04以及之后的版本
Gcc: 4.4.7 toolchain
1.3 硬件平台
Msm8x25,pmic(pm8029)
1.4 开发工具
VIM,SourceInsight,JTAG,ADB
闲话少说，直接进入正题了，在上一篇里写了高通平台android2.3里的kernel和bootloader(LK)里LCD驱动的移植，这一篇主要写一下在4.0里LCD驱动的移植。
二、LCD流程分析
2.1 帧缓冲
2.1.1帧缓冲概念
帧缓冲（framebuffer）是Linux系统为显示设备提供的一个接口，它将显示缓冲区抽象，屏蔽图像硬件的底层差异，允许上层应用程序在图形模式下直接对显示缓冲区进行读写操作。用户不必关系物理显示缓冲区的具体位置及存放方式，这些都由帧缓冲设备驱动本身来完成。对于帧缓冲设备而言，只要在显示缓冲区中与显示点对应的区域写入颜色值，对应的颜色会自动在屏幕上显示。帧缓冲为标准字符设备，主设备号为29，对应于/dev/fbn。
2.1.2 fb_info结构体
帧缓冲设备最关键的一个数据结构体是fb_info结构，为了便于记忆，简称FBI，这个机构体在fb.h文件中定义了。FBI中包括了关于帧缓冲设备属性和操作的完整描述，这个结构体的定义如下所示。
struct fb_info {
atomic_t count;
int node;
int flags;
struct mutex lock; /*用于open/release/ioctl的锁*/
struct mutex mm_lock; /* Lock for fb_mmap and smem_* fields */
struct fb_var_screeninfo var; /* 用户可修改的显示控制参数，包括像素比特数和屏幕分辨率，比如xres、yres、bits_per_pixel等 */
struct fb_fix_screeninfo fix; /* 用户不可修改的显示控制参数 比如物理地址、长度等 */
struct fb_monspecs monspecs; /* Current Monitor specs */
struct work_struct queue; /* Framebuffer event queue */
struct fb_pixmap pixmap; /* Image hardware mapper */
struct fb_pixmap sprite; /* Cursor hardware mapper */
struct fb_cmap cmap; /* Current cmap */
struct list_head modelist; /* mode list */
struct fb_videomode *mode; /* current mode */
#ifdef CONFIG_FB_BACKLIGHT
/* assigned backlight device */
/* set before framebuffer registration,
remove after unregister */
struct backlight_device *bl_dev;
/* Backlight level curve */
struct mutex bl_curve_mutex;
u8 bl_curve[FB_BACKLIGHT_LEVELS];
#endif
#ifdef CONFIG_FB_DEFERRED_IO
struct delayed_work deferred_work;
struct fb_deferred_io *fbdefio;
#endif
struct fb_ops *fbops;/* 帧缓冲操作 */
struct device *device; /* This is the parent */
struct device *dev; /* This is this fb device */
int class_flag; /* private sysfs flags */
#ifdef CONFIG_FB_TILEBLITTING
struct fb_tile_ops *tileops; /* Tile Blitting */
#endif
char __iomem *screen_base; /* Virtual address */
unsigned long screen_size; /* Amount of ioremapped VRAM or 0虚拟内存大小 */
void *pseudo_palette; /* Fake palette of 16 colors伪16色颜色表 */
#define FBINFO_STATE_RUNNING 0
#define FBINFO_STATE_SUSPENDED 1
u32 state; /* Hardware state i.e suspend */
void *fbcon_par; /* fbcon use-only private area */
/* From here on everything is device dependent */
void *par;
/* we need the PCI or similar aperture base/size not
smem_start/size as smem_start may just be an object
allocated inside the aperture so may not actually overlap */
struct apertures_struct {
unsigned int count;
struct aperture {
resource_size_t base;
resource_size_t size;
} ranges[0];
} *apertures;
};
其中fb_ops、fb_var_screeninfo和fb_fix_screeninfo这三个结构极为重要。FBI的成员变量fbops为指向底层操作的函数指针，这些函数是需要驱动程序开发人员编写的，不过高通平台已经定义好这些接口了，我们只需了解下这些接口的功能，不必修改。
fb_var_screeninfo记录用户可修改的显示控制参数，包括屏幕分辨率和每个像素点的比特数。fb_var_screeninfo中的xres定义屏幕一行有多少个点，yres定义屏幕一列有多少个点，bits_per_pixel定义每个点用多少个字节表示。而fb_fix_screeninfo中记录用户不能修改的显示控制器的参数，如屏幕缓冲区的物理地址、长度。当对帧缓冲设备进行映射操作时，就是从fb_fix_screeninfo中取得缓冲区物理地址的。上述结构体都需要在驱动程序中初始化和设置，在后面的流程分析中会作具体的讲解。
fb_ops结构体
struct fb_ops {
/* open/release and usage marking */
struct module *owner;
int (*fb_open)(struct fb_info *info, int user);
int (*fb_release)(struct fb_info *info, int user);
/* For framebuffers with strange non linear layouts or that do not
* work with normal memory mapped access
*/
ssize_t (*fb_read)(struct fb_info *info, char __user *buf,
size_t count, loff_t *ppos);
ssize_t (*fb_write)(struct fb_info *info, const char __user *buf,
size_t count, loff_t *ppos);
/* checks var and eventually tweaks it to something supported,
* DO NOT MODIFY PAR */
int (*fb_check_var)(struct fb_var_screeninfo *var, struct fb_info *info);
/* set the video mode according to info->var */
int (*fb_set_par)(struct fb_info *info);
/* set color register */
int (*fb_setcolreg)(unsigned regno, unsigned red, unsigned green,
unsigned blue, unsigned transp, struct fb_info *info);
/* set color registers in batch */
int (*fb_setcmap)(struct fb_cmap *cmap, struct fb_info *info);
/* blank display */
int (*fb_blank)(int blank, struct fb_info *info);
/* pan display */
int (*fb_pan_display)(struct fb_var_screeninfo *var, struct fb_info *info);
/* Draws a rectangle */
void (*fb_fillrect) (struct fb_info *info, const struct fb_fillrect *rect);
/* Copy data from area to another */
void (*fb_copyarea) (struct fb_info *info, const struct fb_copyarea *region);
/* Draws a image to the display */
void (*fb_imageblit) (struct fb_info *info, const struct fb_image *image);
/* Draws cursor */
int (*fb_cursor) (struct fb_info *info, struct fb_cursor *cursor);
/* Rotates the display */
void (*fb_rotate)(struct fb_info *info, int angle);
/* wait for blit idle, optional */
int (*fb_sync)(struct fb_info *info);
/* perform fb specific ioctl (optional) */
int (*fb_ioctl)(struct fb_info *info, unsigned int cmd,
unsigned long arg);
/* Handle 32bit compat ioctl (optional) */
int (*fb_compat_ioctl)(struct fb_info *info, unsigned cmd,
unsigned long arg);
/* perform fb specific mmap */
int (*fb_mmap)(struct fb_info *info, struct vm_area_struct *vma);
/* get capability given var */
void (*fb_get_caps)(struct fb_info *info, struct fb_blit_caps *caps,
struct fb_var_screeninfo *var);
/* teardown any resources to do with this framebuffer */
void (*fb_destroy)(struct fb_info *info);
/* called at KDB enter and leave time to prepare the console */
int (*fb_debug_enter)(struct fb_info *info);
int (*fb_debug_leave)(struct fb_info *info);
};
文件操作结构体
static const struct file_operations fb_fops = {
.owner = THIS_MODULE,
.read = fb_read,
.write = fb_write,
.unlocked_ioctl = fb_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = fb_compat_ioctl,
#endif
.mmap = fb_mmap,
.open = fb_open,
.release = fb_release,
#ifdef HAVE_ARCH_FB_UNMAPPED_AREA
.get_unmapped_area = get_fb_unmapped_area,
#endif
#ifdef CONFIG_FB_DEFERRED_IO
.fsync = fb_deferred_io_fsync,
#endif
.llseek = default_llseek,
};
2.1.3 帧缓冲设备驱动结构
从上图可以看出，注册framebuffer时需要用到fb_info结构体，fb_info结构体又包含了fb_ops结构体，而fb_ops结构体中的fb_read、fb_write用于应用层对framebuffer的读写操作，fb_mmap用于应用进程和framebuffer之间的内存映射，fb_ioctl用于应用层对framebuffer进行的一些控制操作，具体的操作会在后面的流程分析中讲到。fb_info结构中的fb_check_var和fb_set_par分别用于获取和设置framebuffer的显示参数。
2.2 LCD driver的注册以及framebuffer的建立
在分析LCD的流程时，从底层往上一层层的分析，这样更容易理解驱动层每一层的作用。
需要完成四个工作：
1、申请FBI结构体内存空间，初始化FBI结构体中fb_var_screeninfo var、fb_fix_screeninfo fix。
2、由LCD特点，完成LCD控制器硬件初始化
3、申请帧缓冲设备的显示缓冲区空间
4、注册帧缓冲设备
2.2.1 LCD驱动的注册以及LCDC device的创建
帧缓冲设备驱动的模块加载/卸载以及平台驱动的探测和移除函数
static struct spi_driver lcdc_toshiba_spi_driver = {
.driver = {
.name = LCDC_TOSHIBA_SPI_DEVICE_NAME,
.owner = THIS_MODULE,
},
.probe = lcdc_toshiba_spi_probe,
.remove = __devexit_p(lcdc_toshiba_spi_remove),
};
#endif
static struct platform_driver this_driver = {
.probe = toshiba_probe,
.driver = {
.name = "lcdc_toshiba_wvga",
},
};
static struct msm_fb_panel_data toshiba_panel_data = {
.on = lcdc_toshiba_panel_on,
.off = lcdc_toshiba_panel_off,
.set_backlight = lcdc_toshiba_set_backlight,
};
static struct platform_device this_device = {
.name = "lcdc_toshiba_wvga",
.id = 1,
.dev = {
.platform_data = &toshiba_panel_data,
}
};
static int __devinit toshiba_probe(struct platform_device *pdev)
{
if (pdev->id == 0) {
lcdc_toshiba_pdata = pdev->dev.platform_data;
#ifndef CONFIG_SPI_QSD
spi_pin_assign();
#endif
return 0;
}
msm_fb_add_device(pdev);
return 0;
}
#ifdef CONFIG_SPI_QSD
static int __devinit lcdc_toshiba_spi_probe(struct spi_device *spi)
{
lcdc_toshiba_spi_client = spi;
lcdc_toshiba_spi_client->bits_per_word = 32;
return 0;
#ifdef CONFIG_SPI_QSD
static int __devinit lcdc_toshiba_spi_probe(struct spi_device *spi)
{
lcdc_toshiba_spi_client = spi;
lcdc_toshiba_spi_client->bits_per_word = 32;
return 0;
}
static int __devexit lcdc_toshiba_spi_remove(struct spi_device *spi)
{
lcdc_toshiba_spi_client = NULL;
return 0;
}
在注册LCD驱动前需要设置一些参数，包括分辨率大小、bpp、像素时钟频率等。
pinfo = &toshiba_panel_data.panel_info;
pinfo->xres = 480;
pinfo->yres = 800;
MSM_FB_SINGLE_MODE_PANEL(pinfo);
pinfo->type = LCDC_PANEL;
pinfo->pdest = DISPLAY_1;
pinfo->wait_cycle = 0;
pinfo->bpp = 18;
pinfo->fb_num = 2;
/* 30Mhz mdp_lcdc_pclk and mdp_lcdc_pad_pcl */
pinfo->clk_rate = 30720000;
pinfo->bl_max = 15;
pinfo->bl_min = 1;
pinfo->lcdc.h_back_porch = 184; /* hsw = 8 + hbp=184 */
pinfo->lcdc.h_front_porch = 4;
pinfo->lcdc.h_pulse_width = 8;
pinfo->lcdc.v_back_porch = 2; /* vsw=1 + vbp = 2 */
pinfo->lcdc.v_front_porch = 3;
pinfo->lcdc.v_pulse_width = 1;
pinfo->lcdc.border_clr = 0; /* blk */
pinfo->lcdc.underflow_clr = 0xff; /* blue */
pinfo->lcdc.hsync_skew = 0;
在toshiba_probe函数中会执行msm_fb_add_device(pdev)这个接口，这个接口在msm_fb.c中定义，这个接口的功能就是传递LCD
driver的相关参数并根据LCD的类型（这里假设是RGB接口）创建一个LCDC
device，此外还会创建一个framebuffer结构体，并将其添加到全局的framebuffer列表fb_list里面。
2.2.2 MDP device的创建
在根据LCD的类型创建新设备时，会去执行lcdc.c中的probe函数，这个接口会创建一个mdp
device，然后设置mdp device的一些显示参数以及on和off接口，并将lcdc的pdev结构体的next指针指向mdp
device的设备结构体，即mdp device是lcdc device的父节点。
2.2.3 msm_fbdevice的创建
在创建MDP device时，会去执行mdp.c中的probe函数，初始化MDP相关参数并创建msm_fb
device，其next指针指向mdp device的设备结构体，即msm_fb device是mdp device的父节点。
2.2.4 fb0的创建
在创建msmfb_device时，会去执行msm_fb.c中的probe函数，此接口中最重要的一个函数就是msm_fb_register，该接口会对前面讲到的fb_info结构体进行填充，设置fb_var_screen和fb_fix_screen结构体的显示参数，包括图像显示格式、可见分辨率、虚拟分辨率、红绿蓝色域的偏移、帧率、虚拟基地址等等一些参数，并将高通平台自带的fb_ops接口填充到fb_info结构体里面，然后调用register_framebuffer来创建fb0
device。至此，fb0的建立已经完成，应用层可以对fb0节点的控制来操作framebuffer缓冲区。
2.2.5 fb设备创建流程图
从上图可清楚的看出从注册LCD驱动到创建framebuffer的流程。
2.3 fb设备的打开及framebuffer的使用
上面分析从LCD驱动的注册到fb0建立的流程，那么fb0创建好后，怎么使用它呢？现在来分析下打开fb0操作framebuffer的流程。
2.3.1 gralloc设备的打开过程
显示模块在初始化时会去通过hw_get_module加载gralloc库，该库存在于/system/lib/hw中，在加载成功gralloc库后，会调用framebuffer_open接口，这个接口最终会被指向framebuffer.cpp文件中的fb_device_open函数。执行fb_device_open时，首先会去打开先前已经加载成功的gralloc库。
Gralloc模块在在文件hardware/libhardware/include/hardware/gralloc.h中定义了一个帮助函数gralloc_open，用来打开gralloc设备。gralloc_open最终会指向gralloc.cpp中的gralloc_device_open函数。
int gralloc_device_open(const hw_module_t* module, const char* name,
hw_device_t** device)
{
int status = -EINVAL;
if (!strcmp(name, GRALLOC_HARDWARE_GPU0)) {
gralloc_context_t *dev;
dev = (gralloc_context_t*)malloc(sizeof(*dev));
/* initialize our state here */
memset(dev, 0, sizeof(*dev));
/* initialize the procs */
dev->device.common.tag = HARDWARE_DEVICE_TAG;
dev->device.common.version = 0;
dev->device.common.module = const_cast<hw_module_t*>(module);
dev->device.common.close = gralloc_close;
dev->device.alloc = gralloc_alloc;
dev->device.free = gralloc_free;
*device = &dev->device.common;
status = 0;
} else {
status = fb_device_open(module, name, device);
}
return status;
}
这个函数主要是用来创建一个gralloc_context_t结构体，并且对它的成员变量device进行初始化。结构体gralloc_context_t的成员变量device的类型为gralloc_device_t，它用来描述一个gralloc设备。gralloc设备是用来分配和释放图形缓冲区的，这是通过调用它的成员函数alloc和free来实现的。
2.3.2 fb设备的打开过程
在打开gralloc设备后，会去执行fb_device_open来打开fb设备。fb设备使用结构体framebuffer_device_t来描述。结构体framebuffer_device_t是用来描述系统帧缓冲区的信息，它定义在文hardware/libhardware/include/hardware/fb.h。
typedef struct framebuffer_device_t {
struct hw_device_t common;
/* flags describing some attributes of the framebuffer */
const uint32_t flags;/*记录系统帧缓冲区的标志*/
/* dimensions of the framebuffer in pixels */
const uint32_t width;/*显示屏宽度*/
const uint32_t height;/*显示屏高度*/
/* frambuffer stride in pixels */
const int stride;/*显示屏每行像素点数目*/
/* framebuffer pixel format */
const int format;/帧缓冲区格式/
/* resolution of the framebuffer's display panel in pixel per inch*/
const float xdpi;/*显示屏在宽度上的密度*/
const float ydpi;/*显示屏在高度上的密度*/
/* framebuffer's display panel refresh rate in frames per second */
const float fps;/*描述设备显示屏的刷新频率，它的单位是帧每秒 */
/* min swap interval supported by this framebuffer */
const int minSwapInterval;
/* max swap interval supported by this framebuffer */
const int maxSwapInterval;
int reserved[8];
/*
* requests a specific swap-interval (same definition than EGL)
*
* Returns 0 on success or -errno on error.
*/
int (*setSwapInterval)(struct framebuffer_device_t* window,
int interval);
int (*setUpdateRect)(struct framebuffer_device_t* window,
int left, int top, int width, int height);
int (*post)(struct framebuffer_device_t* dev, buffer_handle_t buffer);
int (*compositionComplete)(struct framebuffer_device_t* dev);
#if defined(OSP_GRALLOC_READ) /* */
int (*read)(struct framebuffer_device_t* dev, buffer_handle_t buffer);
#endif
void (*dump)(struct framebuffer_device_t* dev, char *buff, int buff_len);
/*
* (*enableScreen)() is used to either blank (enable=0) or
* unblank (enable=1) the screen this framebuffer is attached to.
*
* Returns 0 on success or -errno on error.
*/
int (*enableScreen)(struct framebuffer_device_t* dev, int enable);
/*
* Notification to gralloc that the current display rotation angle changed.
*/
void (*setRotation)(struct framebuffer_device_t* dev, int rotation);
void* reserved_proc[6];
} framebuffer_device_t;
Gralloc模块在在文件hardware/libhardware/include/hardware/fb.h中定义了一个帮助函数framebuffer_open，用来打开fb设备。这个接口最终会被指向hardware/qcom/display/libgralloc/framebuffer.cpp文件中的fb_device_open函数。
int fb_device_open(hw_module_t const* module, const char* name,
hw_device_t** device)
{
int status = -EINVAL;
if (!strcmp(name, GRALLOC_HARDWARE_FB0)) {
alloc_device_t* gralloc_device;
status = gralloc_open(module, &gralloc_device);
if (status < 0)
return status;
/* initialize our state here */
fb_context_t *dev = (fb_context_t*)malloc(sizeof(*dev));
memset(dev, 0, sizeof(*dev));
/* initialize the procs */
dev->device.common.tag = HARDWARE_DEVICE_TAG;
dev->device.common.version = 0;
dev->device.common.module = const_cast<hw_module_t*>(module);
dev->device.common.close = fb_close;
dev->device.setSwapInterval = fb_setSwapInterval;
dev->device.post = fb_post;
dev->device.setUpdateRect = 0;
dev->device.compositionComplete = fb_compositionComplete;
private_module_t* m = (private_module_t*)module;
status = mapFrameBuffer(m);
if (status >= 0) {
int stride = m->finfo.line_length / (m->info.bits_per_pixel >> 3);
const_cast<uint32_t&>(dev->device.flags) = 0;
const_cast<uint32_t&>(dev->device.width) = m->info.xres;
const_cast<uint32_t&>(dev->device.height) = m->info.yres;
const_cast<int&>(dev->device.stride) = stride;
const_cast<int&>(dev->device.format) = m->fbFormat;
const_cast<float&>(dev->device.xdpi) = m->xdpi;
const_cast<float&>(dev->device.ydpi) = m->ydpi;
const_cast<float&>(dev->device.fps) = m->fps;
const_cast<int&>(dev->device.minSwapInterval) =
PRIV_MIN_SWAP_INTERVAL;
const_cast<int&>(dev->device.maxSwapInterval) =
PRIV_MAX_SWAP_INTERVAL;
const_cast<int&>(dev->device.numFramebuffers) = m->numBuffers;
if (m->finfo.reserved[0] == 0x5444 &&
m->finfo.reserved[1] == 0x5055) {
dev->device.setUpdateRect = fb_setUpdateRect;
ALOGD("UPDATE_ON_DEMAND supported");
}
*device = &dev->device.common;
}
// Close the gralloc module
gralloc_close(gralloc_device);
}
return status;
fb_device_open用来创建一个fb_context_t结构体，并且对它的成员变量device进行初始化。结构体fb_context_t的成员变量device的类型为framebuffer_device_t，前面提到，它是用来描述fb设备的。fb设备主要是用来渲染图形缓冲区的，这是通过调用它的成员函数post来实现的。从这里可以看出，函数fb_device_open所打开的fb设备的成员函数post被设置为Gralloc模块中的函数fb_post.。
函数fb_device_open在打开fb设备的过程中，会调用另外一个函数mapFrameBuffer来获得系统帧缓冲区的信息，并且将这些信息保存在参数module所描述的一个private_module_t结构体的各个成员变量中。有了系统帧缓冲区的信息之后，函数fb_device_open接下来就可以对前面所打开的一个fb设备的各个成员变量进行初始化。这些成员变量的含义可以参考前面对结构体framebuffer_device_t的介绍。函数mapFrameBuffer除了用来获得系统帧缓冲区的信息之外，还会将系统帧缓冲区映射到当前进程的地址空间来。
函数mapFrameBuffer实现在文件hardware/libhardware/modules/gralloc/framebuffer.cpp，如下所示：
static int mapFrameBuffer(struct private_module_t* module)
{
pthread_mutex_lock(&module->lock);
int err = mapFrameBufferLocked(module);
pthread_mutex_unlock(&module->lock);
return err;
}
这个函数调用了同一个文件中的另外一个函数mapFrameBufferLocked来初始化参数module以及将系统帧缓冲区映射到当前进程的地址空间来。
int mapFrameBufferLocked(struct private_module_t* module)
{
// already initialized...
if (module->framebuffer) {
return 0;
}
char const * const device_template[] = {
"/dev/graphics/fb%u",
"/dev/fb%u",
0 };
int fd = -1;
int i=0;
char name[64];
char property[PROPERTY_VALUE_MAX];
首先在系统中检查是否存在设备文件/dev/graphics/fb0或者/dev/fb0。如果存在的话，那么就调用函数open来打开它，并且将得到的文件描述符保存在变量fd中。这样，接下来函数mapFrameBufferLocked就可以通过文件描述符fd来与内核中的帧缓冲区驱动程序交互
while ((fd==-1) && device_template[i]) {
snprintf(name, 64, device_template[i], 0);
fd = open(name, O_RDWR, 0);
i++;
}
if (fd < 0)
return -errno;
下面代码通过IO控制命令FBIOGET_FSCREENINFO来获得系统帧缓冲区的信息，并存在fb_fix_screeninfo结构体finfo下
struct fb_fix_screeninfo finfo; if (ioctl(fd, FBIOGET_FSCREENINFO, &finfo) == -1) return -errno;
下面代码通过IO控制命令FBIOGET_VSCREENINFO来获得系统帧缓冲区的信息，并存在fb_fix_screeninfo结构体info下
struct fb_var_screeninfo info; if (ioctl(fd, FBIOGET_VSCREENINFO, &info) == -1)
return -errno;
设置设备显示屏的虚拟分辨率，结构体fb_var_screeninfo的成员变量xres和yres用来描述显示屏的可视分辨率，而成员变量xres_virtual和yres_virtual用来描述显示屏的虚拟分辨率。这里保持可视分辨率以及虚拟分辨率的宽度值不变，而将虚拟分辨率的高度值设置为可视分辨率的高度值的NUM_BUF
FERS倍。NUM_BUFFERS是一个宏，它的值被定义为2。这样，我们就可以将系统帧缓冲区划分为两个图形缓冲区来使用，即可以通过硬件来实现双
缓冲技术。在结构体fb_var_screeninfo中，与显示屏的可视分辨率和虚拟分辨率相关的另外两个成员变量是xoffset和yoffset，它们用来告诉帧缓冲区当
前要渲染的图形缓冲区是哪一个
info.reserved[0] = 0;
info.reserved[1] = 0;
info.reserved[2] = 0;
info.xoffset = 0;
info.yoffset = 0;
info.activate = FB_ACTIVATE_NOW;
/* Interpretation of offset for color fields: All offsets are from the
* right, inside a "pixel" value, which is exactly 'bits_per_pixel' wide
* (means: you can use the offset as right argument to <<). A pixel
* afterwards is a bit stream and is written to video memory as that
* unmodified. This implies big-endian byte order if bits_per_pixel is
* greater than 8.
*/
if(info.bits_per_pixel == 32) {
/*
* Explicitly request RGBA_8888
*/
info.bits_per_pixel = 32;
info.red.offset = 24;
info.red.length = 8;
info.green.offset = 16;
info.green.length = 8;
info.blue.offset = 8;
info.blue.length = 8;
info.transp.offset = 0;
info.transp.length = 8;
/* Note: the GL driver does not have a r=8 g=8 b=8 a=0 config, so if we
* do not use the MDP for composition (i.e. hw composition == 0), ask
* for RGBA instead of RGBX. */
if (property_get("debug.sf.hw", property, NULL) > 0 &&
atoi(property) == 0)
module->fbFormat = HAL_PIXEL_FORMAT_RGBX_8888;
else if(property_get("debug.composition.type", property, NULL) > 0 &&
(strncmp(property, "mdp", 3) == 0))
module->fbFormat = HAL_PIXEL_FORMAT_RGBX_8888;
else
module->fbFormat = HAL_PIXEL_FORMAT_RGBA_8888;
} else {
/*
* Explicitly request 5/6/5
*/
info.bits_per_pixel = 16;
info.red.offset = 11;
info.red.length = 5;
info.green.offset = 5;
info.green.length = 6;
info.blue.offset = 0;
info.blue.length = 5;
info.transp.offset = 0;
info.transp.length = 0;
module->fbFormat = HAL_PIXEL_FORMAT_RGB_565;
}
//adreno needs 4k aligned offsets. Max hole size is 4096-1
int size = roundUpToPageSize(info.yres * info.xres *
(info.bits_per_pixel/8));
/*
* Request NUM_BUFFERS screens (at least 2 for page flipping)
*/
int numberOfBuffers = (int)(finfo.smem_len/size);
ALOGV("num supported framebuffers in kernel = %d", numberOfBuffers);
if (property_get("debug.gr.numframebuffers", property, NULL) > 0) {
int num = atoi(property);
if ((num >= NUM_FRAMEBUFFERS_MIN) && (num <= NUM_FRAMEBUFFERS_MAX)) {
numberOfBuffers = num;
}
}
if (numberOfBuffers > NUM_FRAMEBUFFERS_MAX)
numberOfBuffers = NUM_FRAMEBUFFERS_MAX;
ALOGV("We support %d buffers", numberOfBuffers);
//consider the included hole by 4k alignment
uint32_t line_length = (info.xres * info.bits_per_pixel / 8);
info.yres_virtual = (size * numberOfBuffers) / line_len
uint32_t flags = PAGE_FLIP;
if (ioctl(fd, FBIOPUT_VSCREENINFO, &info) == -1) {
info.yres_virtual = size / line_length;
flags &= ~PAGE_FLIP;
ALOGW("FBIOPUT_VSCREENINFO failed, page flipping not supported");
}
if (info.yres_virtual < ((size * 2) / line_length) ) {
// we need at least 2 for page-flipping
info.yres_virtual = size / line_length;
flags &= ~PAGE_FLIP;
ALOGW("page flipping not supported (yres_virtual=%d, requested=%d)",
info.yres_virtual, info.yres*2);
}
if (ioctl(fd, FBIOGET_VSCREENINFO, &info) == -1)
return -errno;
if (int(info.width) <= 0 || int(info.height) <= 0) {
// the driver doesn't return that information
// default to 160 dpi
info.width = ((info.xres * 25.4f)/160.0f + 0.5f);
info.height = ((info.yres * 25.4f)/160.0f + 0.5f);
}
float xdpi = (info.xres * 25.4f) / info.width;
float ydpi = (info.yres * 25.4f) / info.height;
//The reserved[4] field is used to store FPS by the driver.
float fps = info.reserved[4];
通过IO控制命令FBIOGET_FSCREENINFO来获得系统帧缓冲区的固定信息，并且保存在fb_fix_screeninfo结构体finfo中，接下来再使用fb_fix_screeninfo结构体finfo以及前面得到的系统帧缓冲区的其它信息来初始化参数module所描述的一个private_module_t结构体
module->flags = flags;
module->info = info;
module->finfo = finfo;
module->xdpi = xdpi;
module->ydpi = ydpi;
module->fps = fps;
module->swapInterval = 1;
int err;
module->numBuffers = info.yres_virtual / info.yres;/*计算系统帧缓冲区可以换分出多少个缓冲区使用*/
module->bufferMask = 0;
//adreno needs page aligned offsets. Align the fbsize to pagesize.
size_t fbSize = roundUpToPageSize(finfo.line_length * info.yres)*
module->numBuffers;
module->framebuffer = new private_handle_t(fd, fbSize,
private_handle_t::PRIV_FLAGS_USES_PMEM,
BUFFER_TYPE_UI,
module->fbFormat, info.xres, info.yres);
系统帧缓冲区是通过调用函数mmap来映射到当前进程的地址空间来的。映射后得到的地址空间使用一个private_handle_t结构体来描述，这个结构体的成员变量base保存的即为系统帧缓冲区在当前进程的地址空间中的起始地址。这样，Gralloc模块以后就可以从这块地址空间中分配图形缓冲区给当前进程使用
void* vaddr = mmap(0, fbSize, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
if (vaddr == MAP_FAILED) {
ALOGE("Error mapping the framebuffer (%s)", strerror(errno));
return -errno;
}
module->framebuffer->base = intptr_t(vaddr);
memset(vaddr, 0, fbSize);
module->currentOffset = 0;
module->fbPostDone = false;
pthread_mutex_init(&(module->fbPostLock), NULL);
pthread_cond_init(&(module->fbPostCond), NULL);
module->fbPanDone = false;
pthread_mutex_init(&(module->fbPanLock), NULL);
pthread_cond_init(&(module->fbPanCond), NULL);
return 0;
b设备的打开过程的分析完成了，系统缓冲区已经被映射到应用层的进程空间了。在fb设备被打开后，应用层就可以通过ioctl接口对底层的framebuffer进行操作了。
2.3.3 fb设备打开流程图
