[PATCH v3 05/15] pwm: lpss: Use pwm_lpss_apply() when restoring state on resume

Hans de Goede
2020-06-20T12:19:01Z

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.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
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 | 62 ++++++++++++++++++++++++++++++++++++------
1 file changed, 53 insertions(+), 9 deletions(-)

diff --git a/drivers/pwm/pwm-lpss.c b/drivers/pwm/pwm-lpss.c
index 80d0f9c64f9d..4f3d60ce9929 100644
--- a/drivers/pwm/pwm-lpss.c
+++ b/drivers/pwm/pwm-lpss.c
@@ -123,25 +123,31 @@ static inline void pwm_lpss_cond_enable(struct pwm_device *pwm, bool cond)
pwm_lpss_write(pwm, pwm_lpss_read(pwm) | PWM_ENABLE);
}

-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;

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);
@@ -154,12 +160,20 @@ static int pwm_lpss_apply(struct pwm_chip *chip, struct pwm_device *pwm,
}
} 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 0;
}

+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);
+}
+
static void pwm_lpss_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
struct pwm_state *state)
{
@@ -272,10 +286,40 @@ 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_state saved_state;
+ struct pwm_device *pwm;
+ int i, ret;
+ u32 ctrl;

- 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];
+
+ ctrl = pwm_lpss_read(pwm);
+ /* If we did not reach S0i3/S3 the controller keeps its state */
+ if (ctrl == lpwm->saved_ctrl[i])
+ continue;
+
+ /*
+ * 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.
+ * So instead of reproducing all the code from pwm_apply() here,
+ * we just reapply the state as stored in pwm->state.
+ */
+ saved_state = pwm->state;
+ /*
+ * Update enabled to its actual setting for the
+ * enabled<->disabled transitions inside apply().
+ */
+ pwm->state.enabled = !!(ctrl & PWM_ENABLE);
+ ret = __pwm_lpss_apply(&lpwm->chip, pwm, &saved_state, true);
+ if (ret)
+ dev_err(dev, "Error restoring state on resume\n");
+ }

return 0;
}
--
2.26.2