On 3/2/21 3:56 PM, William Breathitt Gray wrote:
> On Tue, Mar 02, 2021 at 03:43:55PM +0100, Fabrice Gasnier wrote:
>> 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.gasn...@foss.st.com>
>
> Acked-by: William Breathitt Gray <vilhelm.g...@gmail.com>
>
> 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
>
>> ---
>> 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
>>
