简要记录了Qualcom MSM8xxx MDP Framebuffer驱动中的一些点。
Framebuffer设备的sysfs
330static int msm_fb_create_sysfs(struct platform_device *pdev)
331{
332 int rc;
333 struct msm_fb_data_type *mfd = platform_get_drvdata(pdev);
334
335 rc = sysfs_create_group(&mfd->fbi->dev->kobj, &msm_fb_attr_group);
336 if (rc)
337 MSM_FB_ERR("%s: sysfs group creation failed, rc=%d\n", __func__,
338 rc);
339 return rc;
340}
root@android:/sys/class/graphics/fb0 # ls -al
-rw-r--r-- root root 4096 1970-06-27 09:37 bits_per_pixel
-rw-r--r-- root root 4096 1970-06-27 09:37 blank
-rw-r--r-- root root 4096 1970-06-27 09:37 console
-rw-r--r-- root root 4096 1970-06-27 09:37 cursor
-r--r--r-- root root 4096 1970-06-27 09:37 dev
-rw-r--r-- root root 4096 1970-06-27 09:37 mode
-rw-r--r-- root root 4096 1970-06-27 09:37 modes
-r--r--r-- root root 4096 1970-06-27 09:37 msm_fb_type
-r--r--r-- root root 4096 1970-06-27 09:37 name
-rw-r--r-- root root 4096 1970-06-27 09:37 pan
drwxr-xr-x root root 1970-06-27 08:28 power
-rw-r--r-- root root 4096 1970-06-27 09:37 rotate
-rw-r--r-- root root 4096 1970-06-27 09:37 state
-r--r--r-- root root 4096 1970-06-27 09:37 stride
lrwxrwxrwx root root 1970-06-27 09:37 subsystem -> ../../../../class/graphics
-rw-r--r-- root root 4096 1970-06-27 08:28 uevent
-rw-r--r-- root root 4096 1970-06-27 09:37 virtual_size
-r--r--r-- root root 4096 1970-06-27 08:28 vsync_event
root@android:/sys/class/graphics/fb0 # cat msm_fb_type
mipi dsi cmd panel
root@android:/sys/class/graphics/fb0 # cat bits_per_pixel
32
130|root@android:/sys/class/graphics/fb0 # cat dev
29:0
root@android:/sys/class/graphics/fb0 # cat modes
U:480x854p-0
root@android:/sys/class/graphics/fb0 # cat name
msmfb42_90501
root@android:/sys/class/graphics/fb0 # cat stride
1920
root@android:/sys/class/graphics/fb0 # cat virtual_size
480,2566
cont_splash_done field
Add support for "Continuous Splash Screen" feature.
The image displayed on the screen by the android bootloaderdriver should continue till the android animation shows up.
Delay the display initialization for MDP, display dependent clocksand panel power on functions.
bootloader显示的image在linux内核启动过程中保持显示在屏幕上，知道开机动画显示，即linux内核启动过程中不要出现黑屏。
Early suspend & Early resume
Early suspend是有wakelock还占有，系统还不能整体suspend，但是可以关闭屏幕、背光、输入等；在Early suspended状态时，重新打开屏幕、背光和输入，是为对应的early resume。
fb_register中相关设置如下：
1551 mfd->early_suspend.suspend = msmfb_early_suspend;
1552 mfd->early_suspend.resume = msmfb_early_resume;
1553 mfd->early_suspend.level = EARLY_SUSPEND_LEVEL_DISABLE_FB - 2;
1554 register_early_suspend(&mfd->early_suspend);
数据结构定义如下：
23/* The early_suspend structure defines suspend and resume hooks to be called
24 * when the user visible sleep state of the system changes, and a level to
25 * control the order. They can be used to turn off the screen and input
26 * devices that are not used for wakeup.
27 * Suspend handlers are called in low to high level order, resume handlers are
28 * called in the opposite order. If, when calling register_early_suspend,
29 * the suspend handlers have already been called without a matching call to the
30 * resume handlers, the suspend handler will be called directly from
31 * register_early_suspend. This direct call can violate the normal level order.
32 */
33enum {
34 EARLY_SUSPEND_LEVEL_BLANK_SCREEN = 50,
35 EARLY_SUSPEND_LEVEL_STOP_DRAWING = 100,
36 EARLY_SUSPEND_LEVEL_DISABLE_FB = 150,
37};
38struct early_suspend {
39#ifdef CONFIG_HAS_EARLYSUSPEND
40 struct list_head link;
41 int level;
42 void (*suspend)(struct early_suspend *h);
43 void (*resume)(struct early_suspend *h);
44#endif
45};
backlight
msm_fb_set_backlight以后是使用led_trigger调用真正led_classdev "wled"的brightnes_set去设置背光。
用户态ioctl通过msm_fb_set_backlight调用到msm_fb_panel_data::set_backlight，
"lcd_backlight".brightness_set -> msm_fb_panel_data::set_backlight -> "bkl_trigger".led_trigger -> "wled".brightness_set。然后找真正操作硬件IC部分。
驱动中设置背光则是绕过"lcd_backlight"设备直接通过backlight_worker工作执行到msm_fb_panel_data::set_backlight，然后-> "bkl_trigger".led_trigger -> "wled".brightness_set。
可以认为"lcd_backlight"是背光抽象设备，通过led_trigger的led组映射到不同的led_classdev设备
以三星DSI CMD屏为例：
In mipi_samsung.c
294static void mipi_samsung_set_backlight(struct msm_fb_data_type *mfd)
295{
296 if (!cci_fb_UpdateDone){
297 printk("Taylor: No BL before LCM on\n");
298 return;
299 }
300
301 pr_debug("Taylor: %s : Set BL:%d\n",__func__, mfd->bl_level);
302 if ((mipi_samsung_pdata->enable_wled_bl_ctrl)
303 && (wled_trigger_initialized)) {
304 led_trigger_event(bkl_led_trigger, mfd->bl_level);
305 return;
306 }
307}
kernel/drivers/leds/leds-pm8xxx.c
#define PM8XXX_LEDS_DEV_NAME "pm8xxx-led"
2283static struct platform_driver pm8xxx_led_driver = {
2284 .probe = pm8xxx_led_probe,
2285 .remove = __devexit_p(pm8xxx_led_remove),
2286 .driver = {
2287 .name = PM8XXX_LEDS_DEV_NAME,
2288 .owner = THIS_MODULE,
2289 },
2290};
pm8xxx_led_probe会对pm8038_led_info数组中的每个led使用设置led_classdev字段，并且初始化work item，然后使用led_classdev_register向系统注册每个led设备。
2197 INIT_WORK(&led_dat->work, pm8xxx_led_work);
2198 INIT_WORK(&led_dat->modework, pm8xxx_mode_work);
2199 INIT_WORK(&led_dat->testwork, pm8xxx_test_work);
每个led的brightness_set字段设置为pm8xxx_led_set。
1790static void pm8xxx_led_set(struct led_classdev *led_cdev,
1791 enum led_brightness value)
1792{
1793 struct pm8xxx_led_data *led;
1794
1795 led = container_of(led_cdev, struct pm8xxx_led_data, cdev);
1796
1797 if (value < LED_OFF || value > led->cdev.max_brightness) {
1798 dev_err(led->cdev.dev, "Invalid brightness value exceeds");
1799 return;
1800 }
1801
1802 led->cdev.brightness = value;
1803 schedule_work(&led->work);
1804}
1730static void pm8xxx_led_work(struct work_struct *work)
1731{
1732 int rc;
1733
1734 struct pm8xxx_led_data *led = container_of(work,
1735 struct pm8xxx_led_data, work);
1736
1737 if (led->pwm_dev == NULL) {
1738 __pm8xxx_led_work(led, led->cdev.brightness);
1739 } else {
1740 rc = pm8xxx_led_pwm_work(led);
1741 if (rc)
1742 pr_err("could not configure PWM mode for LED:%d\n",
1743 led->id);
1744 }
1745}
对PM8XXX_ID_WLED，是使用__pm8xxx_led_work
1692static void __pm8xxx_led_work(struct pm8xxx_led_data *led,
1693 enum led_brightness level)
1694{
1695 int rc;
1696
1697 mutex_lock(&led->lock);
1698
1699 switch (led->id) {
1700 case PM8XXX_ID_LED_KB_LIGHT:
1701 led_kp_set(led, level);
1702 break;
1703 case PM8XXX_ID_LED_0:
1704 case PM8XXX_ID_LED_1:
1705 case PM8XXX_ID_LED_2:
1706 led_lc_set(led, level);
1707 break;
1708 case PM8XXX_ID_FLASH_LED_0:
1709 case PM8XXX_ID_FLASH_LED_1:
1710 led_flash_set(led, level);
1711 break;
1727 mutex_unlock(&led->lock);
1728}
led_wled_set写电源管理芯片pm8xxx的控制寄存器，控制wled。
Framebuffer fb_info::node
registered_fb它是一个数组，它的类型就是struct fb_info，它用于保存我们调用register_framebuffer传进来的struct fb_info。
num_registered_fb代表注册帧缓冲设备的个数。
1522 for (i = 0; i < FB_MAX; i++)
1523 if (!registered_fb[i])
1524 break;
1525 fb_info->node = i;
相当于找到一个空的次设备号。
Framebuffer像素格式
主屏Framebuffer格式 RGBA8888， config时指定；屏格式为RGB565或RGB888，由overlay pipe做转换。
In mipi_dsi_probe()
481 /*
482 * get/set panel specific fb info
483 */
484 mfd->panel_info = pdata->panel_info;
485 pinfo = &mfd->panel_info;
486
487 if (mfd->panel_info.type == MIPI_VIDEO_PANEL)
488 mfd->dest = DISPLAY_LCDC;
489 else
490
492 if (mdp_rev == MDP_REV_303 &&
493 mipi_dsi_pdata->get_lane_config) {
494 if (mipi_dsi_pdata->get_lane_config() != 2) {
495 pr_info("Changing to DSI Single Mode Configuration\n");
496#ifdef CONFIG_FB_MSM_MDP303
497 update_lane_config(pinfo);
498#endif
499 }
500 }
501
502 if (mfd->index == 0)
503 mfd->fb_imgType = MSMFB_DEFAULT_TYPE; // configed as RGBA8888 for fb0
504 else
505 mfd->fb_imgType = MDP_RGB_565;
msmfb_update_notify/ msmfb_no_update_notify
用于CABL功能时，统计直方图使用；
更新屏幕前complete(&msmfb_update_notify)从而在准确时间点启动直方图统计；2*HZ后，msmfb_no_update_notify_timer超时，在timer超时回调中complete(&mfd->msmfb_no_update_notify)结束直方图统计。
sw_refresher
使用定时器去触发mdp_refresh_screen，添加work进行dma_fnc调用。
针对某些接口的VIDEO模式屏且控制器没有hw_refresh支持时，可以使用sw_refresher。
FB_ACTIVATE_VBL标志涵义
fb_var_screeninfo结构体的成员变量activate的值设置FB_ACTIVATE_VBL，表示要等到下一个垂直同步事件出现时，再将当前要渲染的图形缓冲区的内容绘制出来。这样做的目的是避免出现屏幕闪烁，即避免前后两个图形缓冲区的内容各有一部分同时出现屏幕中。