[PATCH] counter: stm32-timer-cnt: fix ceiling write max value

[Fabrice Gasnier]

The ceiling value isn't checked before writing it into registers. The user
could write a value higher than the counter resolution (e.g. 16 or 32 bits
indicated by max_arr). This makes most significant bits to be truncated.
Fix it by checking the max_arr to report a range error [1] to the user.

Fixes: ad29937e206f ("counter: Add STM32 Timer quadrature encoder")

[1] https://lkml.org/lkml/2021/2/12/358

Signed-off-by: Fabrice Gasnier <fabrice.gasnier at foss.st.com>
---
 drivers/counter/stm32-timer-cnt.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/counter/stm32-timer-cnt.c b/drivers/counter/stm32-timer-cnt.c
index ef2a974..2cf0c05 100644
--- a/drivers/counter/stm32-timer-cnt.c
+++ b/drivers/counter/stm32-timer-cnt.c
@@ -32,6 +32,7 @@ struct stm32_timer_cnt {
 	struct regmap *regmap;
 	struct clk *clk;
 	u32 ceiling;
+	u32 max_arr;
 	bool enabled;
 	struct stm32_timer_regs bak;
 };
@@ -185,6 +186,9 @@ static ssize_t stm32_count_ceiling_write(struct counter_device *counter,
 	if (ret)
 		return ret;
 
+	if (ceiling > priv->max_arr)
+		return -ERANGE;
+
 	/* TIMx_ARR register shouldn't be buffered (ARPE=0) */
 	regmap_update_bits(priv->regmap, TIM_CR1, TIM_CR1_ARPE, 0);
 	regmap_write(priv->regmap, TIM_ARR, ceiling);
@@ -360,6 +364,7 @@ static int stm32_timer_cnt_probe(struct platform_device *pdev)
 	priv->regmap = ddata->regmap;
 	priv->clk = ddata->clk;
 	priv->ceiling = ddata->max_arr;
+	priv->max_arr = ddata->max_arr;
 
 	priv->counter.name = dev_name(dev);
 	priv->counter.parent = dev;
-- 
2.7.4