Commit 01aa905d authored May 12, 2020 by Hans de Goede Committed by Thierry Reding Jun 02, 2020

pwm: lpss: Fix get_state runtime-pm reference handling

Before commit cfc4c189 ("pwm: Read initial hardware state at request
time"), a driver's get_state callback would get called once per PWM from
pwmchip_add().

pwm-lpss' runtime-pm code was relying on this, getting a runtime-pm ref for
PWMs which are enabled at probe time from within its get_state callback,
before enabling runtime-pm.

The change to calling get_state at request time causes a number of
problems:

1. PWMs enabled at probe time may get runtime suspended before they are
requested, causing e.g. a LCD backlight controlled by the PWM to turn off.

2. When the request happens when the PWM has been runtime suspended, the
ctrl register will read all 1 / 0xffffffff, causing get_state to store
bogus values in the pwm_state.

3. get_state was using an async pm_runtime_get() call, because it assumed
that runtime-pm has not been enabled yet. If shortly after the request an
apply call is made, then the pwm_lpss_is_updating() check may trigger
because the resume triggered by the pm_runtime_get() call is not complete
yet, so the ctrl register still reads all 1 / 0xffffffff.

This commit fixes these issues by moving the initial pm_runtime_get() call
for PWMs which are enabled at probe time to the pwm_lpss_probe() function;
and by making get_state take a runtime-pm ref before reading the ctrl reg.

BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1828927


Fixes: cfc4c189 ("pwm: Read initial hardware state at request time")
Cc: stable@vger.kernel.org
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

parent 856c45d8

drivers/pwm/pwm-lpss.c

+11 −4

Original line number	Diff line number	Diff line
		@@ -158,7 +158,6 @@ static int pwm_lpss_apply(struct pwm_chip chip, struct pwm_device pwm,
		return 0;
		}

		/* This function gets called once from pwmchip_add to get the initial state */
		static void pwm_lpss_get_state(struct pwm_chip chip, struct pwm_device pwm,
		struct pwm_state *state)
		{
		@@ -167,6 +166,8 @@ static void pwm_lpss_get_state(struct pwm_chip chip, struct pwm_device pwm,
		unsigned long long base_unit, freq, on_time_div;
		u32 ctrl;

		pm_runtime_get_sync(chip->dev);

		base_unit_range = BIT(lpwm->info->base_unit_bits);

		ctrl = pwm_lpss_read(pwm);
		@@ -187,8 +188,7 @@ static void pwm_lpss_get_state(struct pwm_chip chip, struct pwm_device pwm,
		state->polarity = PWM_POLARITY_NORMAL;
		state->enabled = !!(ctrl & PWM_ENABLE);

		if (state->enabled)
		pm_runtime_get(chip->dev);
		pm_runtime_put(chip->dev);
		}

		static const struct pwm_ops pwm_lpss_ops = {
		@@ -202,7 +202,8 @@ struct pwm_lpss_chip pwm_lpss_probe(struct device dev, struct resource *r,
		{
		struct pwm_lpss_chip *lpwm;
		unsigned long c;
		int ret;
		int i, ret;
		u32 ctrl;

		if (WARN_ON(info->npwm > MAX_PWMS))
		return ERR_PTR(-ENODEV);
		@@ -232,6 +233,12 @@ struct pwm_lpss_chip pwm_lpss_probe(struct device dev, struct resource *r,
		return ERR_PTR(ret);
		}

		for (i = 0; i < lpwm->info->npwm; i++) {
		ctrl = pwm_lpss_read(&lpwm->chip.pwms[i]);
		if (ctrl & PWM_ENABLE)
		pm_runtime_get(dev);
		}

		return lpwm;
		}
		EXPORT_SYMBOL_GPL(pwm_lpss_probe);

Admin message