Hi,
On 7/9/20 3:36 PM, Andy Shevchenko wrote:
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(...);
}
...
That is a good idea, I like it. We already had multiple pm_runtime_put() calls
before for the error handlig and this patch did not make it any better.
So adding a pwm_lpss_prepare_enable() helper (the name works for)
will also cleanup the original code. I will add this helper as
a separate preparation patch for this one in v5 of the patch-set.
Regards,
Hans
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