pwm: fsl-ftm: Fix clock enable/disable when using PM

A FTM PWM instance enables/disables three clocks: The bus clock, the
counter clock and the PWM clock. The bus clock gets enabled on
pwm_request, whereas the counter and PWM clocks will be enabled upon
pwm_enable.

The driver has three closesly related issues when enabling/disabling
clocks during suspend/resume:
- The three clocks are not treated differently in regards to the
  individual PWM state enabled/requested. This can lead to clocks
  getting disabled which have not been enabled in the first place
  (a PWM channel which only has been requested going through
  suspend/resume).

- When entering suspend, the current behavior relies on the
  FTM_OUTMASK register: If a PWM output is unmasked, the driver
  assumes the clocks are enabled. However, some PWM instances
  have only 2 channels connected (e.g. Vybrid's FTM1). In that case,
  the FTM_OUTMASK reads 0x3 if all channels are disabled, even if
  the code wrote 0xff to it before. For those PWM instances, the
  current approach to detect enabled PWM signals does not work.

- A third issue applies to the bus clock only, which can get enabled
  multiple times (once for each PWM channel of a PWM chip). This is
  fine, however when entering suspend mode, the clock only gets
  disabled once.

This change introduces a different approach by relying on the enable
and prepared counters of the clock framework and using the frameworks
PWM signal states to address all three issues.

Clocks get disabled during suspend and back enabled on resume
regarding to the PWM channels individual state (requested/enabled).

Since we do not count the clock enables in the driver, this change no
longer clears the Status and Control registers Clock Source Selection
(FTM_SC[CLKS]). However, since we disable the selected clock anyway,
and we explicitly select the clock source on reenabling a PWM channel
this approach should not make a difference in practice.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-fsl-ftm.c

@@ -80,7 +80,6 @@ struct fsl_pwm_chip {
 
 	struct mutex lock;
 
-	unsigned int use_count;
 	unsigned int cnt_select;
 	unsigned int clk_ps;
 
@@ -300,9 +299,6 @@ static int fsl_counter_clock_enable(struct fsl_pwm_chip *fpc)
 {
 	int ret;
 
-	if (fpc->use_count++ != 0)
-		return 0;
-
 	/* select counter clock source */
 	regmap_update_bits(fpc->regmap, FTM_SC, FTM_SC_CLK_MASK,
 			   FTM_SC_CLK(fpc->cnt_select));
@@ -334,25 +330,6 @@ static int fsl_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
 	return ret;
 }
 
-static void fsl_counter_clock_disable(struct fsl_pwm_chip *fpc)
-{
-	/*
-	 * already disabled, do nothing
-	 */
-	if (fpc->use_count == 0)
-		return;
-
-	/* there are still users, so can't disable yet */
-	if (--fpc->use_count > 0)
-		return;
-
-	/* no users left, disable PWM counter clock */
-	regmap_update_bits(fpc->regmap, FTM_SC, FTM_SC_CLK_MASK, 0);
-
-	clk_disable_unprepare(fpc->clk[FSL_PWM_CLK_CNTEN]);
-	clk_disable_unprepare(fpc->clk[fpc->cnt_select]);
-}
-
 static void fsl_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
 {
 	struct fsl_pwm_chip *fpc = to_fsl_chip(chip);
@@ -362,7 +339,8 @@ static void fsl_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
 	regmap_update_bits(fpc->regmap, FTM_OUTMASK, BIT(pwm->hwpwm),
 			   BIT(pwm->hwpwm));
 
-	fsl_counter_clock_disable(fpc);
+	clk_disable_unprepare(fpc->clk[FSL_PWM_CLK_CNTEN]);
+	clk_disable_unprepare(fpc->clk[fpc->cnt_select]);
 
 	regmap_read(fpc->regmap, FTM_OUTMASK, &val);
 	if ((val & 0xFF) == 0xFF)
@@ -492,17 +470,24 @@ static int fsl_pwm_remove(struct platform_device *pdev)
 static int fsl_pwm_suspend(struct device *dev)
 {
 	struct fsl_pwm_chip *fpc = dev_get_drvdata(dev);
-	u32 val;
+	int i;
 
 	regcache_cache_only(fpc->regmap, true);
 	regcache_mark_dirty(fpc->regmap);
 
-	/* read from cache */
-	regmap_read(fpc->regmap, FTM_OUTMASK, &val);
-	if ((val & 0xFF) != 0xFF) {
+	for (i = 0; i < fpc->chip.npwm; i++) {
+		struct pwm_device *pwm = &fpc->chip.pwms[i];
+
+		if (!test_bit(PWMF_REQUESTED, &pwm->flags))
+			continue;
+
+		clk_disable_unprepare(fpc->clk[FSL_PWM_CLK_SYS]);
+
+		if (!pwm_is_enabled(pwm))
+			continue;
+
 		clk_disable_unprepare(fpc->clk[FSL_PWM_CLK_CNTEN]);
 		clk_disable_unprepare(fpc->clk[fpc->cnt_select]);
-		clk_disable_unprepare(fpc->clk[FSL_PWM_CLK_SYS]);
 	}
 
 	return 0;
@@ -511,12 +496,19 @@ static int fsl_pwm_suspend(struct device *dev)
 static int fsl_pwm_resume(struct device *dev)
 {
 	struct fsl_pwm_chip *fpc = dev_get_drvdata(dev);
-	u32 val;
+	int i;
+
+	for (i = 0; i < fpc->chip.npwm; i++) {
+		struct pwm_device *pwm = &fpc->chip.pwms[i];
+
+		if (!test_bit(PWMF_REQUESTED, &pwm->flags))
+			continue;
 
-	/* read from cache */
-	regmap_read(fpc->regmap, FTM_OUTMASK, &val);
-	if ((val & 0xFF) != 0xFF) {
 		clk_prepare_enable(fpc->clk[FSL_PWM_CLK_SYS]);
+
+		if (!pwm_is_enabled(pwm))
+			continue;
+
 		clk_prepare_enable(fpc->clk[fpc->cnt_select]);
 		clk_prepare_enable(fpc->clk[FSL_PWM_CLK_CNTEN]);
 	}