On 3/2/21 3:56 PM, William Breathitt Gray wrote:

On Tue, Mar 02, 2021 at 03:43:55PM +0100, Fabrice Gasnier wrote:

quoted

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@foss.st.com>

Acked-by: William Breathitt Gray <redacted>

Side question: if priv->ceiling is tracking the current ceiling
configuration, would it make sense to change stm32_count_ceiling_read()
to print the value of priv->ceiling instead of doing a regmap_read()
call?

Hi William,

Thanks for reviewing.

I'd be fine either way. So no objection to move to the priv->ceiling
(cached) value. It could also here here.
By looking at this, I figured out there's probably another thing to fix
here, for initial conditions.

At probe time priv->ceiling is initialized to max value (ex 65535 for a
16 bits counter). But the register content is 0 (clear by mfd driver at
probe time).

- So, reading ceiling from sysfs currently reports 0 (regmap_read())
after booting and probing.

I see two cases at this point:
- In case the counter gets enabled without any prior configuration, it
won't count: ceiling value (e.g. 65535) should be written to register
before it is enabled, so the counter will actually count. So there's
room for a fix here.

- In case function gets set (ex: quadrature x4), priv->ceiling (e.g.
65535) gets written to the register (although it's been read earlier as
0 from sysfs).
This could be fixed by reading the priv->ceiling in
stm32_count_ceiling_read() as you're asking (provided 1st case has been
fixed as well)

I'll probably prepare one or two patches for the above cases, if you agree ?

Best Regards,
Fabrice

quoted

---
 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

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