MSM8909开机logo显示(1)---LCD背光的控制

在MSM8909平台上，PWM信号由PMU的MPP2输出，MPP的全称是Multi Purpose Pin，即多用途管脚。在文档80-NN174-64中，说明了MPP2的性质：

PMU输出PWM非常地简单，MSM8909可参考80-NP409，只需配置10个寄存器。对于PWM的输出频率和占空比，高通提供了一个公式来计算：

PWM_FREQ_CLK_SELECT和PWM_SIZE由寄存器0x1BC41配置：

PWM_FREQ_EXPONENT和PWM_FREQ_PRE_DIVIDE由寄存器0x1BC42配置：

0x1BC41和0x1BC42用来配置PWM的输出频率，占空比由寄存器0x1BC44和0x1BC45控制：
                           0x1BC44寄存器

                           0x1BC45寄存器

0x1BC41寄存器的bit2配置为0，即PWM_SIZE = 6，那么0x1BC44寄存器只能配置最低6位。占空比为100%时，0x1BC44寄存器配置为0011 1111，即0x3F。占空比为50%时，0x1BC44寄存器配置为0001 1111，即0x1F。如果0x1BC41寄存器的bit2配置为1，即PWM_SIZE = 9，那么0x1BC45的bit0和0x1BC45的bit0-7组合成9位，占空比的计算方法和6位的计算方法一样。
除了上述4个寄存器配置需要外，还有一个寄存器需要配置，该寄存器位于0x1BC43，配置PWM的输出类型，一般配置该寄存器的bit5为1即可。

上述5个寄存器配置好后，PWM的使能只需配置0x1BC46寄存器的bit7为1即可，同时配置0x1BC47寄存器的bit0为1来更新PWM的计数值，该位置1后会由硬件自动清零。
                          0x1BC46寄存器

                           0x1BC47寄存器

PWM配置好后，还需配置MPP寄存器，需要配置的寄存器有3个。
1.   PM8909的MPP2起始地址位于0xA100。配置0xA140寄存器的bit6-4配置为001，让MPP2为数字输出模式，bit3-0配置为10000，让EN_AND_SOURCE_SEL为DTEST1。

2.   MPP2的输出电压可以通过寄存器0xA141的bit2-0控制。VIN0表示MPP的输出电压等于VPH-PWR，VIN2表示MPP的输出电压和GPIO一样等于1.8V，一般配置为VIN2。

3.   配置0xA146的bit7为1来使能MPP2。

LK中PWM的调用流程如下：

aboot_init的调用
在bootable/bootloader/lk/app/aboot/aboot.c中，有如下定义：

APP_START(aboot)
	.init = aboot_init,
APP_END

APPS_START和APPS_END是宏，在bootable/bootloader/lk/include/app.h中定义：

#define APP_START(appname) struct app_descriptor _app_##appname __SECTION(".apps") = { .name = #appname,
#define APP_END };

宏展开后，如下：

struct app_descriptor _app_aboot __SECTION(".apps") = { 
	.name = "aboot",
	.init = aboot_init,
};

在bootable/bootloader/lk/kernel/main.c中kmain中，新建了一个线程来调用bootstrap2函数。

/* called from crt0.S */
void kmain(void) __NO_RETURN __EXTERNALLY_VISIBLE;
void kmain(void)
{
	......
	// create a thread to complete system initialization
	dprintf(SPEW, "creating bootstrap completion thread\n");
	thread_resume(thread_create("bootstrap2", &bootstrap2, 
		NULL, DEFAULT_PRIORITY, DEFAULT_STACK_SIZE));
}

bootstrap2调用apps_init，apps_init依次取出apps段中所有的init函数，逐一调用。

static int bootstrap2(void *arg)
{
	......
	apps_init();

	return 0;
}

/* one time setup */
void apps_init(void)
{
	const struct app_descriptor *app;

	/* call all the init routines */
	for (app = &__apps_start; app != &__apps_end; app++) {
		if (app->init)
			app->init(app);
	}
	......
}

apps->init(app)调用的就是bootable/bootloader/lk/app/aboot/aboot.c中的aboot_init函数。

mdss_dsi_bl_enable的调用
在gcdb_display_init函数中，将panel结构体的bl_func成员赋值为mdss_dsi_bl_enable：

                                                int gcdb_display_init(const char *panel_name, uint32_t rev, void *base)
{
	......
	if (pan_type == PANEL_TYPE_DSI) {
		......
		panel.panel_info.mipi.mdss_dsi_phy_db = &dsi_video_mode_phy_db;
		panel.pll_clk_func = mdss_dsi_panel_clock;
		panel.power_func = mdss_dsi_panel_power;
		panel.pre_init_func = mdss_dsi_panel_pre_init;
		panel.bl_func = mdss_dsi_bl_enable;   // 背光控制函数被赋值
		panel.fb.base = base;
		panel.fb.width =  panel.panel_info.xres;
		panel.fb.height =  panel.panel_info.yres;
		panel.fb.stride =  panel.panel_info.xres;
		panel.fb.bpp =  panel.panel_info.bpp;
		panel.fb.format = panel.panel_info.mipi.dst_format;
	} else if (pan_type == PANEL_TYPE_EDP) {
		......
	} else {
		......
	}
	......

	ret = msm_display_init(&panel);
	......
}

接下来在msm_display_init函数中，通过pdata->bl_func(1)来调用mdss_dsi_bl_enable函数。

int msm_display_init(struct msm_fb_panel_data *pdata)
{
	......
	/* Turn on backlight */
	if (pdata->bl_func)
		ret = pdata->bl_func(1);
	......
}

背光控制的核心在target_backlight_ctrl函数，该函数在bootable/bootloader/lk/target/msm8909/target_display.c中：

int target_backlight_ctrl(struct backlight *bl, uint8_t enable)
{
    struct pm8x41_mpp mpp;
    uint32_t hw_id = board_hardware_id();
    struct board_pmic_data pmic_info;
    int rc;

    if (bl->bl_interface_type == BL_DCS)
        return 0;

    board_pmic_info(&pmic_info, 1);
    if (pmic_info.pmic_version == PM8916_VER)
        mpp.base = PM8x41_MMP4_BASE;
    else
        mpp.base = PM8x41_MMP2_BASE;   // PM8x41_MMP2_BASE = 0xA100

    mpp.vin = MPP_VIN0;   // MPP_VIN0 = 0
    if (enable) {
        pm_pwm_enable(false);
        rc = pm_pwm_config(PWM_DUTY_US, PWM_PERIOD_US);
        if (rc < 0)
            mpp.mode = MPP_HIGH;
        else {
            mpp.mode = MPP_DTEST1;   // MPP_DTEST1 = 8
            pm_pwm_enable(true);
        }
        pm8x41_config_output_mpp(&mpp);
        pm8x41_enable_mpp(&mpp, MPP_ENABLE);
    } else {
        pm_pwm_enable(false);
        pm8x41_enable_mpp(&mpp, MPP_DISABLE);
    }
    mdelay(20);

    if (enable) {
        if (hw_id == HW_PLATFORM_SURF || (hw_id == HW_PLATFORM_MTP)) {
            /* configure backlight gpio for CDP and MTP */
            gpio_tlmm_config(bkl_gpio.pin_id, 0,
                bkl_gpio.pin_direction, bkl_gpio.pin_pull,
                bkl_gpio.pin_strength, bkl_gpio.pin_state);
                gpio_set(bkl_gpio.pin_id, 2);
        }
    }

    return 0;
}

pm_pwm_enable的分析
bootabl/bootloader/lk/dev/pmic/pm8x41/pm_pwm.c

void pm_pwm_enable(bool enable)
{
	uint8_t reg;
        
        // PM_PWM_ENABLE_CTL_SHIFT = 7
        // PM_PWM_ENABLE_CTL_MASK = 0x80
        // reg = enable << 7 & 0x80;
        reg = enable << PM_PWM_ENABLE_CTL_SHIFT
		& PM_PWM_ENABLE_CTL_MASK;

        // PM_PWM_ENABLE_CTL_REG_OFFSET = 0x46
        pm_pwm_reg_write(PM_PWM_ENABLE_CTL_REG_OFFSET, reg);
}

static void pm_pwm_reg_write(uint8_t off, uint8_t val)
{
	REG_WRITE(PM_PWM_BASE(off), val);
}

bootable/bootloader/lk/dev/pmic/pm8x41/include/pm8x41_hw.h

#define REG_WRITE(_a, _v)   pm8x41_reg_write(_a, _v)

bootable/bootloader/lk/dev/pmic/pm8x41/include/pm_pwm.h

#define PM_PWM_BASE(x)					(0x1BC00 + (x))

从上面的代码可以看出，pm_pwm_enable函数就是控制PM8909的0x1BC46寄存器的bit7。
pm_pwm_config的分析
bootabl/bootloader/lk/dev/pmic/pm8x41/pm_pwm.c

int pm_pwm_config(unsigned int duty_us, unsigned int period_us)
{
	struct pm_pwm_config pwm_config;

	if ((duty_us > period_us) || (period_us > PM_PWM_PERIOD_MAX) ||
	    (period_us < PM_PWM_PERIOD_MIN)) {
		dprintf(CRITICAL, "Error in duty cycle and period\n");
		return -1;
	}

	pm_pwm_calc_period(period_us, &pwm_config);
	pm_pwm_calc_pwm_value(&pwm_config, period_us, duty_us);

	dprintf(SPEW, "duty/period=%u/%u usec: pwm_value=%d (of %d)\n",
		duty_us, period_us, pwm_config.pwm_value, 1 << pwm_config.pwm_size);

	pm_pwm_config_regs(&pwm_config);

	return 0;
}

函数带两个参数，分别表示PWM的占空比和周期，单位是微妙。PWM_DUTY_US和PWM_PERIOD_US这两个参数在bootable/bootloader/lk/target/msm8909/target_display.c中定义，可以根据自己的需要修改：

#define PWM_DUTY_US 13
#define PWM_PERIOD_US 27

在pm_pwm_calc_period函数内部，根据给定的PWM周期和占空比计算出最佳的寄存器配置，即PM8909的0x1BC41和0x1BC42两个寄存器。

static void pm_pwm_calc_period(unsigned int period_us,
				   struct pm_pwm_config *pwm_config)
{
	int	n, m, clk, div;
	int	best_m, best_div, best_clk;
	unsigned int last_err, cur_err, min_err;
	unsigned int tmp_p, period_n;

	n = 6;

	if (period_us < ((unsigned)(-1) / NSEC_PER_USEC))
		period_n = (period_us * NSEC_PER_USEC) >> n;
	else
		period_n = (period_us >> n) * NSEC_PER_USEC;

	if (period_n >= MAX_MPT) {
		n = 9;
		period_n >>= 3;
	}

	min_err = last_err = (unsigned)(-1);
	best_m = 0;
	best_clk = 0;
	best_div = 0;
	for (clk = 0; clk < NUM_REF_CLOCKS; clk++) {
		for (div = 0; div < NUM_PRE_DIVIDE; div++) {
			/* period_n = (PWM Period / N) */
			/* tmp_p = (Pre-divide * Clock Period) * 2^m */
			tmp_p = pt_t[div][clk];
			for (m = 0; m <= PM_PWM_M_MAX; m++) {
				if (period_n > tmp_p)
					cur_err = period_n - tmp_p;
				else
					cur_err = tmp_p - period_n;

				if (cur_err < min_err) {
					min_err = cur_err;
					best_m = m;
					best_clk = clk;
					best_div = div;
				}

				if (m && cur_err > last_err)
					/* Break for bigger cur_err */
					break;

				last_err = cur_err;
				tmp_p <<= 1;
			}
		}
	}

	pwm_config->pwm_size = n;   // 0x1BC41寄存器bit2
	pwm_config->clk = best_clk;   // 0x1BC41寄存器bit1,bit0
	pwm_config->pre_div = best_div;   // 0x1BC42寄存器bit6,bit5
	pwm_config->pre_div_exp = best_m;   // 0x1BC42寄存器bit2,bit1,bi0
}

pm_pwm_calc_pwm_value函数根据占空比计算出0x1BC44和0x1BC45寄存器的配置：

static void pm_pwm_calc_pwm_value(struct pm_pwm_config *pwm_config,
				      unsigned int period_us,
				      unsigned int duty_us)
{
	unsigned int max_pwm_value, tmp;

	/* Figure out pwm_value with overflow handling */
	tmp = 1 << (sizeof(tmp) * 8 - pwm_config->pwm_size);
	if (duty_us < tmp) {
		tmp = duty_us << pwm_config->pwm_size;
		pwm_config->pwm_value = tmp / period_us;
	} else {
		tmp = period_us >> pwm_config->pwm_size;
		pwm_config->pwm_value = duty_us / tmp;
	}
	max_pwm_value = (1 << pwm_config->pwm_size) - 1;
	if (pwm_config->pwm_value > max_pwm_value)
		pwm_config->pwm_value = max_pwm_value;
}

pm_pwm_config_regs函数将6个寄存器的值更新到PM8909的寄存器中：

static void pm_pwm_config_regs(struct pm_pwm_config *pwm_config)
{
	int i;
	uint8_t reg;

	reg = ((pwm_config->pwm_size > 6 ? PM_PWM_SIZE_9_BIT : PM_PWM_SIZE_6_BIT)
		<< PM_PWM_SIZE_SEL_SHIFT)
		& PM_PWM_SIZE_SEL_MASK;
	reg |= (pwm_config->clk + 1) & PM_PWM_CLK_SEL_MASK;
	pwm_config->pwm_ctl[SIZE_CLK] = reg;   // 0x1BC41寄存器

	reg = (pwm_config->pre_div << PM_PWM_PREDIVIDE_SHIFT)
	    & PM_PWM_PREDIVIDE_MASK;
	reg |= pwm_config->pre_div_exp & PM_PWM_M_MASK;
	pwm_config->pwm_ctl[FREQ_PREDIV_CLK] = reg;   // 0x1BC42寄存器

	/* Enable glitch removal by default */
	reg = 1 << PM_PWM_EN_GLITCH_REMOVAL_SHIFT
		& PM_PWM_EN_GLITCH_REMOVAL_MASK;
	pwm_config->pwm_ctl[TYPE_CONFIG] = reg;   // 0x1BC43寄存器

        // 0x1BC44,0x1BC45寄存器
	if (pwm_config->pwm_size > 6) {
		pwm_config->pwm_ctl[VALUE_LSB] = pwm_config->pwm_value
				& PM_PWM_VALUE_BIT7_0;
		pwm_config->pwm_ctl[VALUE_MSB] = (pwm_config->pwm_value >> 8)
				& PM_PWM_VALUE_BIT8;
	} else
		pwm_config->pwm_ctl[VALUE_LSB] = pwm_config->pwm_value
			    & PM_PWM_VALUE_BIT5_0;

        // 更新PM8909的0x1BC41-0x1BC45
	for (i = 0; i < NUM_PWM_CTL_REGS; i++)
		pm_pwm_reg_write(PM_PWM_CTL_REG_OFFSET + i, pwm_config->pwm_ctl[i]);

        // 将0x1BC47寄存器的bit0置1
	reg = 1 & PM_PWM_SYNC_MASK;
	pm_pwm_reg_write(PM_PWM_SYNC_REG_OFFSET, reg);
}

pm8x41_config_output_mpp的分析

void pm8x41_config_output_mpp(struct pm8x41_mpp *mpp)
{
	ASSERT(mpp);

        // 更新PM8909的0xA141寄存器bit2:bit1:bit0=0:0:0
        // VOLTAGE_SEL = VIN0
        // REG_WRITE(((0xA100 + 0x41) + (0 << 16)), 0);
	REG_WRITE(((mpp->base + MPP_DIG_VIN_CTL) + (mpp_slave_id << 16)), mpp->vin);
 
        // 更新PM8909的0xA140寄存器bit6:bit5:bit4:bit3:bit2:bit1:bit0=0:0:1:1:0:0:0
        // MODE = DIGITAL_OUTPUT, EN_AND_SOURCE_SEL = MPP_DTEST1
        // REG_WRITE(((0xA100 + 0x40) + (0 << 16)), 8 | (1 << 4));
	REG_WRITE(((mpp->base + MPP_MODE_CTL) + (mpp_slave_id << 16)), mpp->mode | (MPP_DIGITAL_OUTPUT << MPP_MODE_CTL_MODE_SHIFT));
}

pm8x41_enable_mpp的分析

void pm8x41_enable_mpp(struct pm8x41_mpp *mpp, enum mpp_en_ctl enable)
{
	ASSERT(mpp);

        // 更新PM8909的0xA146寄存去bit7=1
        // PERPH_EN = MPP_ENABLED
        // REG_WRITE(((0xA100 + 0x46) + (0 << 16)), 1 << 7);
	REG_WRITE(((mpp->base + MPP_EN_CTL) + (mpp_slave_id << 16)), enable << MPP_EN_CTL_ENABLE_SHIFT);
}

控制PM8909输出PWM信号，需要配置10个寄存器：
0x1BC41 0x1BC42 0x1BC43 0x1BC44 0x1BC45 0x1BC46 0x1BC47 0xA140 0xA141 0xA146