pwm: lpss: Make pwm_lpss_apply() not rely on existing hardware state

Before this commit pwm_lpss_apply() was assuming 2 pre-conditions
were met by the existing hardware state:

1. That the base-unit and on-time-div read back from the
control register are those actually in use, so that it
can skip setting the update bit if the read-back value
matches the desired values.

2. That the controller is enabled when the cached
pwm_state.enabled says that the controller is enabled.

As the long history of fixes for subtle (often suspend/resume)
lpss-pwm issues shows, these assumptions are not necessary
always true.

1. Specifically is not true on some (*) Cherry Trail devices
with a nasty GFX0._PS3 method which: a. saves the ctrl reg value.
b. sets the base-unit to 0 and writes the update bit to apply/commit
c. restores the original ctrl value without setting the update bit,
so that the 0 base-unit value is still in use.

2. Assumption 2. currently is true, but only because of the code which
saves/restores the state on suspend/resume. By convention restoring the
PWM state should be done by the PWM consumer and the presence of this
code in the pmw-lpss driver is a bug. Therefor the save/restore code will
be dropped in the next patch in this series, after which this assumption
also is no longer true.

This commit changes the pwm_lpss_apply() to not make any assumptions about
the state the hardware is in. Instead it makes pwm_lpss_apply() always
fully program the PWM controller, making it much less fragile.

*) Seen on the Acer One 10 S1003, Lenovo Ideapad Miix 310 and 320 models
and various Medion models.

Acked-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200903112337.4113-7-hdegoede@redhat.com

diff --git a/drivers/pwm/pwm-lpss.c b/drivers/pwm/pwm-lpss.c
index 8a136ba..9c5c721 100644 (file)
--- a/drivers/pwm/pwm-lpss.c
+++ b/drivers/pwm/pwm-lpss.c
@@ -85,7 +85,7 @@ static void pwm_lpss_prepare(struct pwm_lpss_chip *lpwm, struct pwm_device *pwm,
        unsigned long long on_time_div;
        unsigned long c = lpwm->info->clk_rate, base_unit_range;
        unsigned long long base_unit, freq = NSEC_PER_SEC;
-       u32 orig_ctrl, ctrl;
+       u32 ctrl;
 
        do_div(freq, period_ns);
 
@@ -104,16 +104,14 @@ static void pwm_lpss_prepare(struct pwm_lpss_chip *lpwm, struct pwm_device *pwm,
        do_div(on_time_div, period_ns);
        on_time_div = 255ULL - on_time_div;
 
-       orig_ctrl = ctrl = pwm_lpss_read(pwm);
+       ctrl = pwm_lpss_read(pwm);
        ctrl &= ~PWM_ON_TIME_DIV_MASK;
        ctrl &= ~((base_unit_range - 1) << PWM_BASE_UNIT_SHIFT);
        ctrl |= (u32) base_unit << PWM_BASE_UNIT_SHIFT;
        ctrl |= on_time_div;
 
-       if (orig_ctrl != ctrl) {
-               pwm_lpss_write(pwm, ctrl);
-               pwm_lpss_write(pwm, ctrl | PWM_SW_UPDATE);
-       }
+       pwm_lpss_write(pwm, ctrl);
+       pwm_lpss_write(pwm, ctrl | PWM_SW_UPDATE);
 }
 
 static inline void pwm_lpss_cond_enable(struct pwm_device *pwm, bool cond)
@@ -124,8 +122,7 @@ static inline void pwm_lpss_cond_enable(struct pwm_device *pwm, bool cond)
 
 static int pwm_lpss_prepare_enable(struct pwm_lpss_chip *lpwm,
                                   struct pwm_device *pwm,
-                                  const struct pwm_state *state,
-                                  bool enable)
+                                  const struct pwm_state *state)
 {
        int ret;
 
@@ -134,12 +131,12 @@ static int pwm_lpss_prepare_enable(struct pwm_lpss_chip *lpwm,
                return ret;
 
        pwm_lpss_prepare(lpwm, pwm, state->duty_cycle, state->period);
-       pwm_lpss_cond_enable(pwm, enable && lpwm->info->bypass == false);
+       pwm_lpss_cond_enable(pwm, lpwm->info->bypass == false);
        ret = pwm_lpss_wait_for_update(pwm);
        if (ret)
                return ret;
 
-       pwm_lpss_cond_enable(pwm, enable && lpwm->info->bypass == true);
+       pwm_lpss_cond_enable(pwm, lpwm->info->bypass == true);
        return 0;
 }
 
@@ -152,11 +149,11 @@ static int pwm_lpss_apply(struct pwm_chip *chip, struct pwm_device *pwm,
        if (state->enabled) {
                if (!pwm_is_enabled(pwm)) {
                        pm_runtime_get_sync(chip->dev);
-                       ret = pwm_lpss_prepare_enable(lpwm, pwm, state, true);
+                       ret = pwm_lpss_prepare_enable(lpwm, pwm, state);
                        if (ret)
                                pm_runtime_put(chip->dev);
                } else {
-                       ret = pwm_lpss_prepare_enable(lpwm, pwm, state, false);
+                       ret = pwm_lpss_prepare_enable(lpwm, pwm, state);
                }
        } else if (pwm_is_enabled(pwm)) {
                pwm_lpss_write(pwm, pwm_lpss_read(pwm) & ~PWM_ENABLE);