On Fri, Jul 17, 2020 at 03:37:43PM +0200, Hans de Goede wrote: > Before this commit a suspend + resume of the LPSS PWM controller > would result in the controller being reset to its defaults of > output-freq = clock/256, duty-cycle=100%, until someone changes > to the output-freq and/or duty-cycle are made. > > This problem has been masked so far because the main consumer > (the i915 driver) was always making duty-cycle changes on resume. > With the conversion of the i915 driver to the atomic PWM API the > driver now only disables/enables the PWM on suspend/resume leaving > the output-freq and duty as is, triggering this problem. > > The LPSS PWM controller has a mechanism where the ctrl register value > and the actual base-unit and on-time-div values used are latched. When > software sets the SW_UPDATE bit then at the end of the current PWM cycle, > the new values from the ctrl-register will be latched into the actual > registers, and the SW_UPDATE bit will be cleared. > > The problem is that before this commit our suspend/resume handling > consisted of simply saving the PWM ctrl register on suspend and > restoring it on resume, without setting the PWM_SW_UPDATE bit. > When the controller has lost its state over a suspend/resume and thus > has been reset to the defaults, just restoring the register is not > enough. We must also set the SW_UPDATE bit to tell the controller to > latch the restored values into the actual registers. > > Fixing this problem is not as simple as just or-ing in the value which > is being restored with SW_UPDATE. If the PWM was enabled before we must > write the new settings + PWM_SW_UPDATE before setting PWM_ENABLE. > We must also wait for PWM_SW_UPDATE to become 0 again and depending on the > model we must do this either before or after the setting of PWM_ENABLE. > > All the necessary logic for doing this is already present inside > pwm_lpss_apply(), so instead of duplicating this inside the resume > handler, this commit makes the resume handler use pwm_lpss_apply() to > restore the settings when necessary. This fixes the output-freq and > duty-cycle being reset to their defaults on resume. ... > -static int pwm_lpss_apply(struct pwm_chip *chip, struct pwm_device *pwm, > - const struct pwm_state *state) > +static int __pwm_lpss_apply(struct pwm_chip *chip, struct pwm_device *pwm, > + const struct pwm_state *state, bool from_resume) > { > struct pwm_lpss_chip *lpwm = to_lpwm(chip); > int ret = 0; > > if (state->enabled) { > if (!pwm_is_enabled(pwm)) { > - pm_runtime_get_sync(chip->dev); > + if (!from_resume) > + pm_runtime_get_sync(chip->dev); > + > ret = pwm_lpss_prepare_enable(lpwm, pwm, state, true); > - if (ret) > + if (ret && !from_resume) > pm_runtime_put(chip->dev); > } else { > ret = pwm_lpss_prepare_enable(lpwm, pwm, state, false); > } > } else if (pwm_is_enabled(pwm)) { > pwm_lpss_write(pwm, pwm_lpss_read(pwm) & ~PWM_ENABLE); > - pm_runtime_put(chip->dev); > + > + if (!from_resume) > + pm_runtime_put(chip->dev); > } > > return ret; > } Maybe I'm too picky, but I would go even further and split apply to two versions static int pwm_lpss_apply_on_resume(struct pwm_chip *chip, struct pwm_device *pwm, const struct pwm_state *state) > { > struct pwm_lpss_chip *lpwm = to_lpwm(chip); > > if (state->enabled) > return pwm_lpss_prepare_enable(lpwm, pwm, state, !pwm_is_enabled(pwm)); > if (pwm_is_enabled(pwm)) { > pwm_lpss_write(pwm, pwm_lpss_read(pwm) & ~PWM_ENABLE); > return 0; > } and another one for !from_resume. > +static int pwm_lpss_apply(struct pwm_chip *chip, struct pwm_device *pwm, > + const struct pwm_state *state) > +{ > + return __pwm_lpss_apply(chip, pwm, state, false); > +} ... > + ret = __pwm_lpss_apply(&lpwm->chip, pwm, &saved_state, true); > + if (ret) > + dev_err(dev, "Error restoring state on resume\n"); I'm wondering if it's a real error why we do not bail out? Otherwise dev_warn() ? -- With Best Regards, Andy Shevchenko