Linux的LCD驱动分析及移植
宿主机平台：Ubuntu 12.04.4 LTS
目标机：Easy-ARM IMX283
目标机内核：Linux 2.6.35.3
LCD屏的驱动总体上分成两块，一块是GUI显示输出驱动；一块是触摸驱动（该部分单独一节另外描述）。
LCD驱动概念
LCD是Liquid Crystal Display的简称，也就是经常所说的液晶显示器。LCD能够支持彩色图像的显示和视频的播放，是一种非常重要的输出设备。如果我们的系统要用GUI（图形界面接口），比如minigui，MicroWindows。这时LCD设备驱动程序就应该编写成frambuffer接口，而不是编写成仅仅操作底层的LCD控制器接口。
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操作。framebuffer又叫帧缓冲，是Linux为操作显示设备提供的一个用户接口。用户应用程序可以通过framebuffer透明地访问不同类型的显示设备。从这个方面来说，framebuffer是硬件设备显示缓冲区的抽象。Linux抽象出framebuffer这个帧缓冲区可以供用户应用程序直接读写，通过更改framebuffer中的内容，就可以立刻显示在LCD显示屏上。
framebuffer是一个标准的字符设备，主设备号是29，次设备号根据缓冲区的数目而定。framebuffer对应/dev/fb%d设备文件。根据显卡的多少，设备文件可能是/dev/fb0、/dev/fb1等。缓冲区设备也是一种普通的内存设备,可以直接对其进行读写。对用户程序而言，它和/dev下面的其他设备没有什么区别，用户可以把frameBuffer看成一块内存，既可以写，又可以读。显示器将根据内存数据显示对应的图像界面。这一切都由LCD控制器和响应的驱动程序来完成。
LCD驱动框架分析
总体上是一个平台设备驱动与字符驱动的组合；
先从LCD的设备 dev/fb* 是怎么实现的来进行追溯；
1.开发板启动，进行设备注册；
在 arch/arm/mach-mx28/device.c 设备注册文件中，注册LCD的fd平台设备 “mxs-fb”
// mxs-fb平台设备资源定义
static struct resource framebuffer_resource[] = {
{
.flags = IORESOURCE_MEM,
.start = LCDIF_PHYS_ADDR,
.end = LCDIF_PHYS_ADDR + 0x2000 - 1,
},
{
.flags = IORESOURCE_IRQ,
.start = IRQ_LCDIF,
.end = IRQ_LCDIF,
},
};
// mxs-fb平台设备私有数据，包含显示屏名称、分辨率、位宽、时钟、面板操作等，在drivers/video/mxs/lcd_43wvf1g.c 中通过subsys_initcall 接口将设备私有数据添加到链表中
static struct mxs_platform_fb_data mxs_framebuffer_pdata = {
.list = LIST_HEAD_INIT(mxs_framebuffer_pdata.list),
};
// lcd设备启动初始化，在 m28evk.c 中 mx28_device_init()会调用
static void __init mx28_init_lcdif(void) { struct platform_device *pdev; pdev = mxs_get_device("mxs-fb", 0); //获取匹配的设备结构体，定义在 arch/arm/plat-mxs/device.c 中
if (pdev == NULL || IS_ERR(pdev)) return; pdev->resource = framebuffer_resource; pdev->num_resources = ARRAY_SIZE(framebuffer_resource); pdev->dev.platform_data = &mxs_framebuffer_pdata; mxs_add_device(pdev, 3); // 添加到设备注册列表，设备注册在 arch/arm/plat-mxs/device.c 中实现 通过 device_initcall(mxs_device_init);遍历设备列表并进行平台设备注册
}
2.接下来是 platform_driver mxsfb_driver 的注册，匹配之后触发 mxsfb_probe 函数执行以下操作：
进行相关硬件初始化和 framebuffer 设置；
register_framebuffer() 注册 LCD 屏的 fd 设备;
LCD的驱动包含：
drivers/video/mxs/lcd_43wvf1g.c // LCD设备私有数据，包含名称、分辨率、位宽、时钟、面板操作
drivers/video/mxs/lcdif.c // lcd的一些接口操作
drivers/video/mxs/mxsfb.c //
平台设备驱动 platform_driver 注册 _drivers/video/mxs/mxsfb.c_
会编译成 mxsfb.ko
static struct platform_driver mxsfb_driver = {
.probe = mxsfb_probe,
.remove = mxsfb_remove,
.suspend = mxsfb_suspend,
.resume = mxsfb_resume,
.driver = {
.name = "mxs-fb", // 与启动时的平台设备注册的 platform_device 名称相同
.owner = THIS_MODULE,
},
};
static int __init mxsfb_init(void)
{
return platform_driver_register(&mxsfb_driver); // 显示屏平台设备驱动注册
}
驱动安装时与平台设备匹配之后触发 mxsfb_probe 函数，这个时核心。
static int __devinit mxsfb_probe(struct platform_device *pdev)
{
int ret = 0;
struct mxs_fb_data *data;
struct resource *res;
struct fb_info *info;
struct mxs_platform_fb_data *pdata = pdev->dev.platform_data;
struct mxs_platform_fb_entry *pentry = NULL;
mydbg("\\n");
if (pdata == NULL) {
ret = -ENODEV;
goto out;
}
if (default\_panel\_name) {
mydbg("default\_panel\_name=%s\\n",default\_panel\_name); // 通过LCD面板名称匹配获取面板参数及设置句柄（平台设备私有数据传递过来）
pentry = (void *)mxs_lcd_iterate_pdata(pdata,
get_matching_pentry_by_name,
default_panel_name);
if (pentry) {
mxs_lcd_move_pentry_up(pentry, pdata);
pdata->cur = pentry;
}
}
if (!default_panel_name || !pentry) {
mydbg("\n");
pentry = pdata->cur;
}
if (!pentry || !pentry->init_panel || !pentry->run_panel ||
!pentry->release_panel) {
mydbg("\n");
ret = -EINVAL;
goto out;
}
data =
(struct mxs\_fb\_data \*)framebuffer\_alloc(sizeof(struct mxs\_fb\_data) +
sizeof(u32) \* 256 -
sizeof(struct fb\_info),
&pdev->dev);
if (data == NULL) {
ret = -ENOMEM;
goto out;
}
cdata = data;
data->dev = &pdev->dev;
data->pdata = pdata;
platform\_set\_drvdata(pdev, data);
info = &data->info;
dev\_dbg(&pdev->dev, "resolution %dx%d, bpp %d\\n", pentry->x\_res,
pentry->y\_res, pentry->bpp);
mxs\_lcd\_iterate\_pdata(pdata, get\_max\_memsize, data);
data->map\_size = PAGE\_ALIGN(data->mem\_size) \* NUM\_SCREENS;
dev\_dbg(&pdev->dev, "memory to allocate: %d\\n", data->map\_size);
data->virt\_start = dma\_alloc\_writecombine(&pdev->dev,
data->map\_size,
&data->phys\_start,
GFP\_KERNEL);
if (data->virt\_start == NULL) {
ret = -ENOMEM;
goto out\_dma;
}
dev\_dbg(&pdev->dev, "allocated at %p:0x%x\\n", data->virt\_start,
data->phys\_start);
mutex\_init(&data->blank\_mutex);
INIT\_WORK(&data->work, mxsfb\_task);
data->state = F\_ENABLE;
mxsfb\_default.bits\_per\_pixel = pentry->bpp;
/\* NB: rotated \*/
mxsfb\_default.xres = pentry->y\_res;
mxsfb\_default.yres = pentry->x\_res;
mxsfb\_default.xres\_virtual = pentry->y\_res;
mxsfb\_default.yres\_virtual = data->map\_size /
(pentry->y\_res \* pentry->bpp / 8);
if (mxsfb\_default.yres\_virtual >= mxsfb\_default.yres \* 2)
mxsfb\_default.yres\_virtual = mxsfb\_default.yres \* 2;
else
mxsfb\_default.yres\_virtual = mxsfb\_default.yres;
mxsfb\_fix.smem\_start = data->phys\_start;
mxsfb\_fix.smem\_len = pentry->y\_res \* pentry->x\_res \* pentry->bpp / 8;
mxsfb\_fix.ypanstep = 1;
switch (pentry->bpp) {
case 32:
case 24:
mxsfb\_default.red.offset = 16;
mxsfb\_default.red.length = 8;
mxsfb\_default.green.offset = 8;
mxsfb\_default.green.length = 8;
mxsfb\_default.blue.offset = 0;
mxsfb\_default.blue.length = 8;
break;
case 16: #if 0
mxsfb_default.red.offset = 11;
mxsfb_default.red.length = 5;
mxsfb_default.green.offset = 5;
mxsfb_default.green.length = 6;
mxsfb_default.blue.offset = 0;
mxsfb_default.blue.length = 5;
break;
#else
mxsfb_default.red.offset = 0 ;
mxsfb_default.red.length = 5;
mxsfb_default.green.offset = 5;
mxsfb_default.green.length = 6;
mxsfb_default.blue.offset = 11;
mxsfb_default.blue.length = 5;
break;
#endif
default:
dev_err(&pdev->dev, "unsupported bitwidth %d\n", pentry->bpp);
ret = -EINVAL;
goto out_dma;
}
info->screen\_base = data->virt\_start;
info->fbops = &mxsfb\_ops;
info->var = mxsfb\_default;
info->fix = mxsfb\_fix;
info->pseudo\_palette = &data->par;
data->par = NULL;
info->flags = FBINFO\_FLAG\_DEFAULT;
init\_waitqueue\_head(&data->vsync\_wait\_q);
data->vsync\_count = 0;
res = platform\_get\_resource(pdev, IORESOURCE\_MEM, 0);
if (res == NULL) {
dev\_err(&pdev->dev, "cannot get IRQ resource\\n");
ret = -ENODEV;
goto out\_dma;
}
data->regbase = (unsigned long)IO\_ADDRESS(res->start);
res = platform\_get\_resource(pdev, IORESOURCE\_IRQ, 0);
if (res == NULL) {
dev\_err(&pdev->dev, "cannot get IRQ resource\\n");
ret = -ENODEV;
goto out\_dma;
}
data->irq = res->start;
mxsfb\_check\_var(&info->var, info);
ret = fb\_alloc\_cmap(&info->cmap, 256, 0);
if (ret)
goto out\_cmap;
mxsfb\_set\_par(info);
mxs\_init\_lcdif();
ret = pentry->init\_panel(data->dev, data->phys\_start,
mxsfb\_fix.smem\_len, pentry);
if (ret) {
dev\_err(&pdev->dev, "cannot initialize LCD panel\\n");
goto out\_panel;
}
dev\_dbg(&pdev->dev, "LCD panel initialized\\n");
init\_timings(data); // not effect dotclk mode
ret = request\_irq(data->irq, lcd\_irq\_handler, 0, "fb\_irq", data);
if (ret) {
dev\_err(&pdev->dev, "request\_irq (%d) failed with error %d\\n",
data->irq, ret);
goto out\_panel;
}
ret = register\_framebuffer(info); // 注册fb\_info
if (ret)
goto out\_irq;
pentry->run\_panel();
/\* REVISIT: temporary workaround for MX23EVK \*/
mxsfb\_disable\_controller(data);
mxsfb\_enable\_controller(data);
data->cur\_phys = data->phys\_start;
dev\_dbg(&pdev->dev, "LCD running now\\n");#ifdef CONFIG_CPU_FREQ
mxsfb_nb.fb_data = data;
cpufreq_register_notifier(&mxsfb_nb.nb, CPUFREQ_TRANSITION_NOTIFIER);
#endif /* CONFIG_CPU_FREQ */
goto out;out_irq:
free_irq(data->irq, data);
out_panel:
fb_dealloc_cmap(&info->cmap);
out_cmap:
dma_free_writecombine(&pdev->dev, data->map_size, data->virt_start,
data->phys_start);
out_dma:
kfree(data);
out:
return ret;
}
待续…..
LCD驱动移植总结
1.LCD引脚配置及初始化
上述原理图包含了数据、时钟、背光控制、触摸、复位等引脚的分配，具体有机会在深入理解LCD硬件驱动原理有在进行说明。
在 arch/arm/mach-mx28/mx28evk_pins.c 的 mx28evk_fixed_pins[ ] 引脚列表中添加 LCD 的驱动引脚，相关引脚转义在 mx28_pins.h 结合 arch/arm/mach/pinctrl.h 实现
#if defined(CONFIG_FB_MXS) || defined(CONFIG_FB_MXS_MODULE)
{
.name = "LCD_D00",
.id = PINID_LCD_D00,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D01",
.id = PINID_LCD_D01,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D02",
.id = PINID_LCD_D02,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D03",
.id = PINID_LCD_D03,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D04",
.id = PINID_LCD_D04,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D05",
.id = PINID_LCD_D05,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D06",
.id = PINID_LCD_D06,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D07",
.id = PINID_LCD_D07,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D08",
.id = PINID_LCD_D08,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D09",
.id = PINID_LCD_D09,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D10",
.id = PINID_LCD_D10,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D11",
.id = PINID_LCD_D11,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D12",
.id = PINID_LCD_D12,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D13",
.id = PINID_LCD_D13,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D14",
.id = PINID_LCD_D14,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D15",
.id = PINID_LCD_D15,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
/*
{
.name = "LCD_D16",
.id = PINID_LCD_D16,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D17",
.id = PINID_LCD_D17,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D18",
.id = PINID_LCD_D18,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D19",
.id = PINID_LCD_D19,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D20",
.id = PINID_LCD_D20,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D21",
.id = PINID_LCD_D21,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D22",
.id = PINID_LCD_D22,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_D23",
.id = PINID_LCD_D23,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
*/
{
.name = "LCD_RESET",
.id = PINID_LCD_RESET,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_VSYNC",
.id = PINID_LCD_RD_E,
.fun = PIN_FUN2,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_HSYNC",
.id = PINID_LCD_WR_RWN,
.fun = PIN_FUN2,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_ENABLE",
.id = PINID_LCD_CS,
.fun = PIN_FUN2,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_DOTCLK",
.id = PINID_LCD_RS,
.fun = PIN_FUN2,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
{
.name = "LCD_BACKLIGHT",
.id = PINID_PWM3,
.fun = PIN_FUN1,
.strength = PAD_8MA,
.voltage = PAD_3_3V,
.drive = 1,
},
#endif
然后通过类似 LCDIF_PHYS_ADDR + BM_LCDIF_CTRL1_RESET 组合就可以操作相关引脚寄存器了
2. 驱动移植到drivers 目录
1）.将LCD驱动放到 drivers/video/ 目录下，本例为 mxs
2）.修改 _drivers/video/Kconfig，添加如下配置，表示会提取 mxs 驱动的 Kconfig 配置_
if ARCH_MXS
source "drivers/video/mxs/Kconfig"
endif
3. 修改板级文件
板级文件有两个
mach-mx28 // mx28系列特有的
plat-mxs // fsl通用共有的功能
1）在设备注册 arch/arm/mach-mx28/device.c 中添加 mxs LCD 平台设备注册
#if defined(CONFIG_FB_MXS) || defined(CONFIG_FB_MXS_MODULE)
// LCD平台设备资源 resource
static struct resource framebuffer_resource[] = {
{
.flags = IORESOURCE_MEM, //寻址地址空间资源
.start = LCDIF\_PHYS\_ADDR,
.end = LCDIF\_PHYS\_ADDR + 0x2000 - 1,
},
{
.flags = IORESOURCE\_IRQ, //中断资源
.start = IRQ\_LCDIF,
.end = IRQ\_LCDIF,
}, };
static struct mxs_platform_fb_data mxs_framebuffer_pdata = {
.list = LIST_HEAD_INIT(mxs_framebuffer_pdata.list),
};
static void __init mx28_init_lcdif(void)
{
struct platform_device *pdev;
pdev = mxs_get_device("mxs-fb", 0); //获取匹配的设备结构体，定义在 arch/arm/plat-mxs/device.c 中
if (pdev == NULL || IS_ERR(pdev))
return;
pdev->resource = framebuffer_resource;
pdev->num_resources = ARRAY_SIZE(framebuffer_resource);
pdev->dev.platform_data = &mxs_framebuffer_pdata; //设备私有数据链表，包含名称、分辨率、位宽、时钟、面板操作，在drivers/video/mxs/lcd_43wvf1g.c 中通过__subsys_initcall 接口将设备私有数据添加到链表中
mxs\_add\_device(pdev, 3); //添加到设备注册列表 }
#else
static void __init mx28_init_lcdif(void)
{
;
}
#endif
2）在设备列表注册 arch/arm/plat-mxs/device.c 中添加 mxs LCD 平台设备结构及设备列表匹配信息
#if defined(CONFIG_FB_MXS) || defined(CONFIG_FB_MXS_MODULE)
// LCD面板平台设备结构体
static struct platform_device mxs_fb = {
.name = "mxs-fb", //平台设备名称，后面的平台设备驱动名称要与这个一致
.id = 0,
.dev = {
.dma_mask = &common_dmamask,
.coherent_dma_mask = DMA_BIT_MASK(32),
.release = mxs_nop_release,
},
};
#endif
static struct mxs_dev_lookup dev_lookup[] = {
……
#if defined(CONFIG_FB_MXS) || defined(CONFIG_FB_MXS_MODULE)
{
.name = "mxs-fb",
.size = 1,
.pdev = &mxs_fb,
},
#endif
……
}
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