On Thu, Sep 03, 2020 at 01:23:26PM +0200, Hans de Goede wrote:
Before this commit pwm_lpss_apply() was assuming 2 pre-conditions were met by the existing hardware state:
- 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.
- 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.
- 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.
- 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.
Good one! Reviewed-by: Andy Shevchenko andriy.shevchenko@linux.intel.com
Acked-by: Thierry Reding thierry.reding@gmail.com Signed-off-by: Hans de Goede hdegoede@redhat.com
Changes in v10:
- Fixup some wording / mistakes in the commit message
Changes in v9:
- This is a new patch in v9 of this series
drivers/pwm/pwm-lpss.c | 21 +++++++++------------ 1 file changed, 9 insertions(+), 12 deletions(-)
diff --git a/drivers/pwm/pwm-lpss.c b/drivers/pwm/pwm-lpss.c index 8a136ba2a583..9c5c7217c9b6 100644 --- 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);
ret = pwm_lpss_prepare_enable(lpwm, pwm, state, false);
ret = pwm_lpss_prepare_enable(lpwm, pwm, state);-- 2.28.0