设备树（DTS）的引入减少了内核为支持新硬件而需要的改变，提高代码重用，使得单个内核镜像能支持多个系统。
DTS作为U-Boot 和Linux 内核之间的动态接口，能够有效减少重复配置，共享于U-Boot 和Linux之间。本文将简单介绍U-Boot使用DTS控制LED的例子：
1.在kernel/arch/arm/boot/dts/rk3288-box.dts中添加LED配置：
------------------- kernel/arch/arm/boot/dts/rk3288-box.dts -------------------
index e102714..80928ba 100755
@@ -137,6 +136,16 @@
rockchip,remote_wakeup;
rockchip,usb_irq_wakeup;
};
+
+ leds {
+ compatible = "gpio-leds";
+ power {
+ label = "tchip:blue:power";
+ default-state = "on";
+ gpios = <&gpio8 GPIO_A3 GPIO_ACTIVE_LOW>;
+ };
+ };
};
&gmac {
以上是linux标准的GPIO-LED配置，直接配置上内核就可使用LED。
2.修改U-Boot，以支持读取DTS配置并操作LED灯，修改u-boot/board/rockchip/rk32xx/rk32xx.c：
-------------------- u-boot/board/rockchip/rk32xx/rk32xx.c --------------------
index bfdcf0e..29fff0f 100755
@@ -61,12 +61,34 @@ void board_lmb_reserve(struct lmb *lmb) {
//reserve 48M for kernel & 8M for nand api.
lmb_reserve(lmb, gd->bd->bi_dram[0].start, CONFIG_LMB_RESERVE_SIZE);
}
+
+static struct fdt_gpio_state power_led_gpio;
+int power_led_parse_dt(const void *blob)
+{
+ int led_node = 0;
+ int node = 0;
+
+ node = fdt_node_offset_by_compatible(blob,
+ 0, "gpio-leds");
+ if (node < 0) {
+ printf("can't find dts node for led\n");
+ return -ENODEV;
+ }
+ led_node = fdt_subnode_offset(blob, node, "power");
+ fdtdec_decode_gpio(blob, led_node, "gpios", &power_led_gpio);
+ power_led_gpio.gpio = rk_gpio_base_to_bank(power_led_gpio.gpio & RK_GPIO_BANK_MASK) | (power_led_gpio.gpio & RK_GPIO_PIN_MASK);
+ power_led_gpio.flags = !(power_led_gpio.flags & OF_GPIO_ACTIVE_LOW);
+ debug("power_led_gpio: %s,%d-%d\n", power_led_gpio.name, power_led_gpio.gpio, power_led_gpio.flags);
+
+ return 0;
+}
#endif /* CONFIG_OF_LIBFDT */
#ifdef CONFIG_RK_FB
#ifdef CONFIG_OF_LIBFDT
+
static struct fdt_gpio_state lcd_en_gpio, lcd_cs_gpio;
static int lcd_en_delay, lcd_cs_delay;
static int lcd_node = 0;
@@ -114,7 +136,6 @@ void rk_backlight_ctrl(int brightness)
void rk_fb_init(unsigned int onoff)
{
-
#ifdef CONFIG_OF_LIBFDT
if (lcd_node == 0) rk_lcd_parse_dt(gd->fdt_blob);
@@ -178,6 +199,17 @@ void init_panel_info(vidinfo_t *vid)
vid->logo_rgb_mode = RGB565;
}
+void power_led_init(void)
+{
+ printf("Enter power_led_init\n");
+#ifdef CONFIG_OF_LIBFDT
+ power_led_parse_dt(gd->fdt_blob);
+ if (power_led_gpio.name!=NULL)
+ {
+ gpio_direction_output(power_led_gpio.gpio, power_led_gpio.flags);
+ }
+#endif
+}
#ifdef CONFIG_RK616
int rk616_power_on(void)
@@ -259,6 +291,9 @@ int board_late_init(void)
load_disk_partitions();
prepare_fdt();
key_init();
+
+ power_led_init();
+
#ifdef CONFIG_POWER_RK
pmic_init(0);
fg_init(0); /*fuel gauge init*/
3.编译内核，参考Wiki<http://wiki.t-firefly.com/index.php/Firefly-RK3288/Build_kernel>中的编译内核映像部分
4.编译U-Boot，参考SDK下的“RKDocs/common/uboot/RockChip_Uboot开发文档V1.0.pdf”文档，编译生成RK3288Loader_uboot_V2.15.bin
5.烧写resource.img和RK3288Loader_uboot_V2.15.bin，开机。有没有发现LED灯比原来的快差不多两秒点亮呢