发生异常的现象：
msm8953 lcd在快速亮灭的情况下背光概率性休眠不灭；测量高通pwm，发现正常的时候pwm的管脚LCM_BL_PWM为低电平，失败的时候为高电平；
根据原理图：
mpp是什么？
mpp是基于电源pmic的管脚，也叫做多功能管脚；MPP的全称是Multi Purpose Pin；可以做电源、gpio、ADC、PWM、SINK等功能。
背光的控制方式：
- LCD控制IC支持动态背光控制功能（CABC）通过解析图像的直方图动态改变输出PWM的占空比从而动态调节LCD的背光，在不改变图像显示效果的情况下降低功耗，PMIC根据CABC的占空比控制背光输出电压；
- 背光控制部分不经过PMIC而是通过一颗单独的带有boost转换功能的LED驱动器如LM3630A，该芯片通过PWM调节亮度。
我们使用的就是第一种方式；
通过soc->pmi8950(内部pwm)->mpp3的方式去控制。
lcd背光控制调用流程：
首先，我们用的是mipi接口，所以lcd显示驱动是在mdss_dsi.c中，pwm驱动控制是在pwm-qpnp.c文件中(kernel\msm-3.18\drivers\pwm);
在mdss_dsi.c文件中，具体在哪里调用到背光函数呢？
根据打印log，可以知道背光控制函数mdss_dsi_panel_bl_ctrl；
mdss_dsi_panel_bl_ctrl这个函数是在mdss_dsi_panel.c文件中；
调用顺序如下:mdss_dsi_ctrl_probe -- >
mdss_dsi_config_panel -- >
mdss_dsi_panel_init -- >
ctrl_pdata->panel_data.set_backlight = mdss_dsi_panel_bl_ctrl;
根据mdss_dsi_panel_bl_ctrl函数：
static void mdss_dsi_panel_bl_ctrl(struct mdss_panel_data *pdata,
u32 bl_level)
{
......
/*
* Some backlight controllers specify a minimum duty cycle
* for the backlight brightness. If the brightness is less
* than it, the controller can malfunction.
*/
if ((bl_level < pdata->panel_info.bl_min) && (bl_level != 0))
bl_level = pdata->panel_info.bl_min;
switch (ctrl_pdata->bklt_ctrl) {
case BL_WLED:
led_trigger_event(bl_led_trigger, bl_level);
break;
case BL_PWM:
mdss_dsi_panel_bklt_pwm(ctrl_pdata, bl_level);
break;
case BL_DCS_CMD:
if (!mdss_dsi_sync_wait_enable(ctrl_pdata)) {
mdss_dsi_panel_bklt_dcs(ctrl_pdata, bl_level);
break;
}
/*
* DCS commands to update backlight are usually sent at
* the same time to both the controllers. However, if
* sync_wait is enabled, we need to ensure that the
* dcs commands are first sent to the non-trigger
* controller so that when the commands are triggered,
* both controllers receive it at the same time.
*/
sctrl = mdss_dsi_get_other_ctrl(ctrl_pdata);
if (mdss_dsi_sync_wait_trigger(ctrl_pdata)) {
if (sctrl)
mdss_dsi_panel_bklt_dcs(sctrl, bl_level);
mdss_dsi_panel_bklt_dcs(ctrl_pdata, bl_level);
} else {
mdss_dsi_panel_bklt_dcs(ctrl_pdata, bl_level);
if (sctrl)
mdss_dsi_panel_bklt_dcs(sctrl, bl_level);
}
break;
default:
pr_err("%s: Unknown bl_ctrl configuration\n",
__func__);
break;
}
}
我们进入mdss_dsi_panel_bklt_pwm函数来看看：
static void mdss_dsi_panel_bklt_pwm(struct mdss_dsi_ctrl_pdata *ctrl, int level)
{
int ret;
u32 duty;
u32 period_ns;
if (ctrl->pwm_bl == NULL) {
pr_err("%s: no PWM\n", __func__);
return;
}
if (level == 0) {
if (ctrl->pwm_enabled) {
ret = pwm_config_us(ctrl->pwm_bl, level,
ctrl->pwm_period);
if (ret)
pr_err("%s: pwm_config_us() failed err=%d.\n",
__func__, ret);
pwm_disable(ctrl->pwm_bl);
}
ctrl->pwm_enabled = 0;
return;
}
....
}
进入pwm_disable函数，这里有调用了一个回调函数：
/**
* pwm_disable() - stop a PWM output toggling
* @pwm: PWM device
*/
void pwm_disable(struct pwm_device *pwm)
{
if (pwm && test_and_clear_bit(PWMF_ENABLED, &pwm->flags)) {
pwm->chip->ops->disable(pwm->chip, pwm);
}
}
搜索之后，可以在qpnp_pwm_disable（pwm-qpnp.c文件中找到相应的函数和函数集）:
static struct pwm_ops qpnp_pwm_ops = {
.enable = qpnp_pwm_enable,
.disable = qpnp_pwm_disable,
.config = qpnp_pwm_config,
.free = qpnp_pwm_free,
.owner = THIS_MODULE,
};
/**
* qpnp_pwm_disable - stop a PWM output toggling
* @pwm_chip: the PWM chip
* @pwm: the PWM device
*/
static void qpnp_pwm_disable(struct pwm_chip *pwm_chip,
struct pwm_device *pwm)
{
struct qpnp_pwm_chip *chip = qpnp_pwm_from_pwm_chip(pwm_chip);
unsigned long flags;
int rc = 0;
spin_lock_irqsave(&chip->lpg_lock, flags);
if (QPNP_IS_PWM_CONFIG_SELECTED(
chip->qpnp_lpg_registers[QPNP_ENABLE_CONTROL]) ||
chip->flags & QPNP_PWM_LUT_NOT_SUPPORTED)
rc = qpnp_lpg_configure_pwm_state(chip,
QPNP_PWM_DISABLE);
else if (!(chip->flags & QPNP_PWM_LUT_NOT_SUPPORTED))
rc = qpnp_lpg_configure_lut_state(chip,
QPNP_LUT_DISABLE);
if (!rc)
chip->enabled = false;
spin_unlock_irqrestore(&chip->lpg_lock, flags);
if (rc)
pr_err("Failed to disable PWM channel: %d\n",
chip->channel_id);
}
来到qpnp_lpg_configure_pwm_state(chip, QPNP_PWM_DISABLE);这个函数中来：
static int qpnp_lpg_configure_pwm_state(struct qpnp_pwm_chip *chip,
enum qpnp_pwm_state state)
{
struct qpnp_lpg_config *lpg_config = &chip->lpg_config;
u8 value, mask;
int rc;
bool test_enable;
if (chip->sub_type == QPNP_PWM_MODE_ONLY_SUB_TYPE) {
if (state == QPNP_PWM_ENABLE)
value = QPNP_ENABLE_PWM_MODE_ONLY_SUB_TYPE;
else
value = QPNP_DISABLE_PWM_MODE_ONLY_SUB_TYPE;
mask = QPNP_PWM_MODE_ONLY_ENABLE_DISABLE_MASK_SUB_TYPE;
} else {
if (state == QPNP_PWM_ENABLE)
value = qpnp_enable_pwm_mode(chip);
else
value = QPNP_DISABLE_PWM_MODE(chip);
mask = QPNP_EN_PWM_HIGH_MASK | QPNP_EN_PWM_LO_MASK |
QPNP_PWM_SRC_SELECT_MASK | QPNP_PWM_EN_RAMP_GEN_MASK;
if (chip->sub_type != QPNP_LPG_S_CHAN_SUB_TYPE)
mask |= QPNP_EN_PWM_OUTPUT_MASK;
}
if (chip->in_test_mode) {
test_enable = (state == QPNP_PWM_ENABLE) ? 1 : 0;
rc = qpnp_dtest_config(chip, test_enable);
if (rc)
pr_err("Failed to configure TEST mode\n");
}
pr_debug("pwm_enable_control: %d\n", value);
rc = qpnp_lpg_save_and_write(value, mask,
&chip->qpnp_lpg_registers[QPNP_ENABLE_CONTROL],
SPMI_LPG_REG_ADDR(lpg_config->base_addr,
QPNP_ENABLE_CONTROL), 1, chip);
if (rc)
goto out;
/*
* Due to LPG hardware bug, in the PWM mode, having enabled PWM,
* We have to write PWM values one more time.
*/
if (state == QPNP_PWM_ENABLE)
return qpnp_lpg_save_pwm_value(chip);
out:
return rc;
}
qpnp_lpg_save_pwm_value会保存着上一次pwm的高低电平的值，
rc = qpnp_lpg_save_and_write(value, mask,
&chip->qpnp_lpg_registers[QPNP_PWM_VALUE_LSB],
SPMI_LPG_REG_ADDR(lpg_config->base_addr,
QPNP_PWM_VALUE_LSB), 1, chip);
保存了上一次亮屏的时候的电平值；所以只要把这段语句去掉，在快速闪灭屏的时候，灭屏就不会出现背光不灭的情况，这是因为寄存器没有写好前，就保存亮屏的高电平值；
LCD背光驱动
在qpnp_lpg_init进入probe函数中，spmi驱动是什么呢？参考这篇文章：
SPMI理解
其实简单理解spmi就是一个通讯协议；
static int qpnp_pwm_probe(struct spmi_device *spmi)
{
struct qpnp_pwm_chip *pwm_chip;
int rc;
pwm_chip = kzalloc(sizeof(*pwm_chip), GFP_KERNEL);
if (pwm_chip == NULL) {
pr_err("kzalloc() failed.\n");
return -ENOMEM;
}
spin_lock_init(&pwm_chip->lpg_lock);
pwm_chip->spmi_dev = spmi;
dev_set_drvdata(&spmi->dev, pwm_chip);
rc = qpnp_parse_dt_config(spmi, pwm_chip);
if (rc) {
pr_err("Failed parsing DT parameters, rc=%d\n", rc);
goto failed_config;
}
pwm_chip->chip.dev = &spmi->dev;
pwm_chip->chip.ops = &qpnp_pwm_ops;
pwm_chip->chip.base = -1;
pwm_chip->chip.npwm = 1;
rc = pwmchip_add(&pwm_chip->chip);
if (rc < 0) {
pr_err("pwmchip_add() failed: %d\n", rc);
goto failed_insert;
}
if (pwm_chip->channel_owner)
pwm_chip->chip.pwms[0].label = pwm_chip->channel_owner;
pr_debug("PWM device sid:%d channel:%d probed successfully\n",
spmi->sid, pwm_chip->channel_id);
return 0;
failed_insert:
kfree(pwm_chip->lpg_config.lut_config.duty_pct_list);
failed_config:
dev_set_drvdata(&spmi->dev, NULL);
kfree(pwm_chip);
return rc;
}
pwm_chip->chip.ops = &qpnp_pwm_ops;注册相应的回调函数；