Re: [PATCH] counter: stm32-timer-cnt: fix ceiling miss-alignment with reload register

William Breathitt Gray
2021-03-04T00:16:57Z

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On Wed, Mar 03, 2021 at 06:49:49PM +0100, Fabrice Gasnier wrote:
> Ceiling value may be miss-aligned with what's actually configured into the
> ARR register. This is seen after probe as currently the ARR value is zero,
> whereas ceiling value is set to the maximum. So:
> - reading ceiling reports zero
> - in case the counter gets enabled without any prior configuration,
> it won't count.
> - in case the function gets set by the user 1st, (priv->ceiling) is used.
>
> Fix it by getting rid of the cached "priv->ceiling" variable. Rather use
> the ARR register value directly by using regmap read or write when needed.
> There should be no drawback on performance as priv->ceiling isn't used in
> performance critical path.
> There's also no point in writing ARR while setting function (sms), so
> it can be safely removed.
>
> Fixes: ad29937e206f ("counter: Add STM32 Timer quadrature encoder")
>
> Suggested-by: William Breathitt Gray <vilhelm.gray@gmail.com>
> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>

Acked-by: William Breathitt Gray <vilhelm.gray@gmail.com>

> ---
> Note: this applies on top of:
> - "counter: stm32-timer-cnt: fix ceiling write max value"

Note, if your patch requires prerequisite patches, please provide the
`git patch-id --stable` patch ID for it; this helps make sure the
patches are applied in the correct order. You can have `git
format-patch` generate this automatically for you by using the `--base`
option:
https://git-scm.com/docs/git-format-patch#_base_tree_information

William Breathitt Gray

> ---
> drivers/counter/stm32-timer-cnt.c | 11 +++--------
> 1 file changed, 3 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/counter/stm32-timer-cnt.c b/drivers/counter/stm32-timer-cnt.c
> index 2295be3..75bc401 100644
> --- a/drivers/counter/stm32-timer-cnt.c
> +++ b/drivers/counter/stm32-timer-cnt.c
> @@ -31,7 +31,6 @@ struct stm32_timer_cnt {
> struct counter_device counter;
> struct regmap *regmap;
> struct clk *clk;
> - u32 ceiling;
> u32 max_arr;
> bool enabled;
> struct stm32_timer_regs bak;
> @@ -75,8 +74,10 @@ static int stm32_count_write(struct counter_device *counter,
> const unsigned long val)
> {
> struct stm32_timer_cnt *const priv = counter->priv;
> + u32 ceiling;
>
> - if (val > priv->ceiling)
> + regmap_read(priv->regmap, TIM_ARR, &ceiling);
> + if (val > ceiling)
> return -EINVAL;
>
> return regmap_write(priv->regmap, TIM_CNT, val);
> @@ -138,10 +139,6 @@ static int stm32_count_function_set(struct counter_device *counter,
>
> regmap_update_bits(priv->regmap, TIM_CR1, TIM_CR1_CEN, 0);
>
> - /* 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, priv->ceiling);
> -
> regmap_update_bits(priv->regmap, TIM_SMCR, TIM_SMCR_SMS, sms);
>
> /* Make sure that registers are updated */
> @@ -199,7 +196,6 @@ static ssize_t stm32_count_ceiling_write(struct counter_device *counter,
> regmap_update_bits(priv->regmap, TIM_CR1, TIM_CR1_ARPE, 0);
> regmap_write(priv->regmap, TIM_ARR, ceiling);
>
> - priv->ceiling = ceiling;
> return len;
> }
>
> @@ -374,7 +370,6 @@ 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);
> --
> 2.7.4
>

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