pwm: stm32: Fix enable count for clk in .probe()

Make the driver take over hardware state without disabling in .probe()
and enable the clock for each enabled channel.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
[ukleinek: split off from a patch that also implemented .get_state()]
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Fixes: 7edf736 ("pwm: Add driver for STM32 plaftorm")
Reviewed-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-stm32.c

@@ -605,17 +605,21 @@ static void stm32_pwm_detect_complementary(struct stm32_pwm *priv)
 	priv->have_complementary_output = (ccer != 0);
 }
 
-static unsigned int stm32_pwm_detect_channels(struct stm32_pwm *priv)
+static unsigned int stm32_pwm_detect_channels(struct stm32_pwm *priv,
+					      unsigned int *num_enabled)
 {
-	u32 ccer;
+	u32 ccer, ccer_backup;
 
 	/*
 	 * If channels enable bits don't exist writing 1 will have no
 	 * effect so we can detect and count them.
 	 */
+	regmap_read(priv->regmap, TIM_CCER, &ccer_backup);
 	regmap_set_bits(priv->regmap, TIM_CCER, TIM_CCER_CCXE);
 	regmap_read(priv->regmap, TIM_CCER, &ccer);
-	regmap_clear_bits(priv->regmap, TIM_CCER, TIM_CCER_CCXE);
+	regmap_write(priv->regmap, TIM_CCER, ccer_backup);
+
+	*num_enabled = hweight32(ccer_backup & TIM_CCER_CCXE);
 
 	return hweight32(ccer & TIM_CCER_CCXE);
 }
@@ -626,6 +630,8 @@ static int stm32_pwm_probe(struct platform_device *pdev)
 	struct device_node *np = dev->of_node;
 	struct stm32_timers *ddata = dev_get_drvdata(pdev->dev.parent);
 	struct stm32_pwm *priv;
+	unsigned int num_enabled;
+	unsigned int i;
 	int ret;
 
 	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
@@ -648,7 +654,11 @@ static int stm32_pwm_probe(struct platform_device *pdev)
 
 	priv->chip.dev = dev;
 	priv->chip.ops = &stm32pwm_ops;
-	priv->chip.npwm = stm32_pwm_detect_channels(priv);
+	priv->chip.npwm = stm32_pwm_detect_channels(priv, &num_enabled);
+
+	/* Initialize clock refcount to number of enabled PWM channels. */
+	for (i = 0; i < num_enabled; i++)
+		clk_enable(priv->clk);
 
 	ret = devm_pwmchip_add(dev, &priv->chip);
 	if (ret < 0)