On Wed, Jul 08, 2020 at 11:14:21PM +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, bool from_resume){ struct pwm_lpss_chip *lpwm = to_lpwm(chip); int ret;
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_is_updating(pwm); if (ret) {
pm_runtime_put(chip->dev);
if (!from_resume)pm_runtime_put(chip->dev);return ret; } pwm_lpss_prepare(lpwm, pwm, state->duty_cycle, state->period); pwm_lpss_cond_enable(pwm, lpwm->info->bypass == false); ret = pwm_lpss_wait_for_update(pwm); if (ret) {
pm_runtime_put(chip->dev);
if (!from_resume)pm_runtime_put(chip->dev);return ret; } pwm_lpss_cond_enable(pwm, lpwm->info->bypass == true);
}} 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);
I'm wondering if splitting more will make this look better, like:
... if (from_resume) { ret = pwm_lpss_prepare_enable(...); // whatever name you think suits better } else { pm_runtime_get_sync(...); ret = pwm_lpss_prepare_enable(...); if (ret) pm_runtime_put(...); } ...