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
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