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

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 4 Mar 2021 08:42:03 +0900
William Breathitt Gray <vilhelm.gray@gmail.com> wrote:

> 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")
Note, I've dropped the blank line here. Fixes is part of the tag block.
> > 
> > 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>

applied to the fixes-togreg branch of iio.git and marked for stable.
Given both this and previous are marked such they should get picked
up fine even without the clean cross reference.

Jonathan
> 
> > ---
> > 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
> >