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 adds a new pwm_lpss_restore() helper which mirrors pwm_lpss_apply() minus the runtime-pm reference handling (which we should not change on resume).
This fixes the output-freq and duty-cycle being reset to their defaults on resume.
Reviewed-by: Andy Shevchenko andriy.shevchenko@linux.intel.com Signed-off-by: Hans de Goede hdegoede@redhat.com --- Changes in v8: - Drop optimization to skip restore if current ctrl reg is the same as our saved ctrl reg value (because this causes issues on some devices) - Simplify pwm_lpss_restore_state() to not rely on the current state - Modify commit message to mention the new pwm_lpss_restore_state() helper
Changes in v6: - Add a pwm_lpss_restore_state() helper for re-applying the PWM state on resume
Changes in v5: - The changes to pwm_lpss_apply() are much cleaner now thanks to the new pwm_lpss_prepare_enable() helper.
Changes in v3: - This replaces the "pwm: lpss: Set SW_UPDATE bit when enabling the PWM" patch from previous versions of this patch-set, which really was a hack working around the resume issue which this patch fixes properly. --- drivers/pwm/pwm-lpss.c | 40 +++++++++++++++++++++++++++++++++++++--- 1 file changed, 37 insertions(+), 3 deletions(-)
diff --git a/drivers/pwm/pwm-lpss.c b/drivers/pwm/pwm-lpss.c index 8a136ba2a583..9a7400c6fb6e 100644 --- a/drivers/pwm/pwm-lpss.c +++ b/drivers/pwm/pwm-lpss.c @@ -166,6 +166,25 @@ static int pwm_lpss_apply(struct pwm_chip *chip, struct pwm_device *pwm, return ret; }
+/* + * This is a mirror of pwm_lpss_apply() without relying on the current state + * (no pwm_is_enabled() calls) and without pm_runtime reference handling, + * for restoring the PWM state on resume. + */ +static int pwm_lpss_restore_state(struct pwm_lpss_chip *lpwm, + struct pwm_device *pwm, + const struct pwm_state *state) +{ + int ret = 0; + + if (state->enabled) + ret = pwm_lpss_prepare_enable(lpwm, pwm, state, true); + else + pwm_lpss_write(pwm, pwm_lpss_read(pwm) & ~PWM_ENABLE); + + return ret; +} + static void pwm_lpss_get_state(struct pwm_chip *chip, struct pwm_device *pwm, struct pwm_state *state) { @@ -278,10 +297,25 @@ EXPORT_SYMBOL_GPL(pwm_lpss_suspend); int pwm_lpss_resume(struct device *dev) { struct pwm_lpss_chip *lpwm = dev_get_drvdata(dev); - int i; + struct pwm_device *pwm; + int i, ret;
- for (i = 0; i < lpwm->info->npwm; i++) - writel(lpwm->saved_ctrl[i], lpwm->regs + i * PWM_SIZE + PWM); + for (i = 0; i < lpwm->info->npwm; i++) { + pwm = &lpwm->chip.pwms[i]; + + /* + * We cannot just blindly restore the old value here. Since we + * are changing the settings we must set SW_UPDATE and 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. + */ + ret = pwm_lpss_restore_state(lpwm, pwm, &pwm->state); + if (ret) + dev_err(dev, "Error restoring state on resume\n"); + }
return 0; }