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

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Date:   Thu, 4 Mar 2021 08:42:03 +0900
From:   William Breathitt Gray <vilhelm.gray@...il.com>
To:     Fabrice Gasnier <fabrice.gasnier@...s.st.com>
Cc:     jic23@...nel.org, alexandre.torgue@...s.st.com,
        mcoquelin.stm32@...il.com, olivier.moysan@...s.st.com,
        linux-iio@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] counter: stm32-timer-cnt: fix ceiling miss-alignment
 with reload register

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@...il.com>
> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@...s.st.com>

Acked-by: William Breathitt Gray <vilhelm.gray@...il.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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