[PATCH v5 08/10] counter: stm32-timer-cnt: probe number of channels from registers

[Fabrice Gasnier]

Probe the number of capture compare channels, by writing CCER register bits
and read them back. Take care to restore the register original value.

This is a precursor patch to support capture channels.

Reviewed-by: William Breathitt Gray <william.gray@xxxxxxxxxx>
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@xxxxxxxxxxx>
---
Changes in v5:
- Add William's Reviewed-by tag.

Changes in v4:
- directly use dev struct in stm32_timer_cnt_detect_channels routine.

Changes in v3:
- New patch split from:
  "counter: stm32-timer-cnt: populate capture channels and check encoder"
---
 drivers/counter/stm32-timer-cnt.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/counter/stm32-timer-cnt.c b/drivers/counter/stm32-timer-cnt.c
index f63d0c3e3f22..e1c0a502b74c 100644
--- a/drivers/counter/stm32-timer-cnt.c
+++ b/drivers/counter/stm32-timer-cnt.c
@@ -42,6 +42,7 @@ struct stm32_timer_cnt {
 	bool enabled;
 	struct stm32_timer_regs bak;
 	bool has_encoder;
+	unsigned int nchannels;
 };
 
 static const enum counter_function stm32_count_functions[] = {
@@ -416,6 +417,20 @@ static struct counter_count stm32_counts = {
 	.num_ext = ARRAY_SIZE(stm32_count_ext)
 };
 
+static void stm32_timer_cnt_detect_channels(struct device *dev,
+					    struct stm32_timer_cnt *priv)
+{
+	u32 ccer, ccer_backup;
+
+	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_write(priv->regmap, TIM_CCER, ccer_backup);
+	priv->nchannels = hweight32(ccer & TIM_CCER_CCXE);
+
+	dev_dbg(dev, "has %d cc channels\n", priv->nchannels);
+}
+
 /* encoder supported on TIM1 TIM2 TIM3 TIM4 TIM5 TIM8 */
 #define STM32_TIM_ENCODER_SUPPORTED	(BIT(0) | BIT(1) | BIT(2) | BIT(3) | BIT(4) | BIT(7))
 
@@ -484,6 +499,8 @@ static int stm32_timer_cnt_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
+	stm32_timer_cnt_detect_channels(dev, priv);
+
 	counter->name = dev_name(dev);
 	counter->parent = dev;
 	counter->ops = &stm32_timer_cnt_ops;
-- 
2.25.1