linux-kernel - Re: [PATCH] mfd: stm32-timers: avoid clearing auto reload register

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Date:   Mon, 22 Mar 2021 12:56:38 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Fabrice Gasnier <fabrice.gasnier@...s.st.com>
Cc:     vilhelm.gray@...il.com, alexandre.torgue@...s.st.com,
        mcoquelin.stm32@...il.com, olivier.moysan@...s.st.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH] mfd: stm32-timers: avoid clearing auto reload register

On Mon, 22 Mar 2021, Fabrice Gasnier wrote:

> On 3/3/21 6:51 PM, Fabrice Gasnier wrote:
> > The ARR register is cleared unconditionally upon probing, after the maximum
> > value has been read. This initial condition is rather not intuitive, when
> > considering the counter child driver. It rather expects the maximum value
> > by default:
> > - The counter interface shows a zero value by default for 'ceiling'
> >   attribute.
> > - Enabling the counter without any prior configuration makes it doesn't
> >   count.
> > 
> > The reset value of ARR register is the maximum. So Choice here
> > is to backup it, and restore it then, instead of clearing its value.
> > It also fixes the initial condition seen by the counter driver.
> > 
> > Fixes: d0f949e220fd ("mfd: Add STM32 Timers driver")
> > 
> > Signed-off-by: Fabrice Gasnier <fabrice.gasnier@...s.st.com>
> > ---
> >  drivers/mfd/stm32-timers.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> Hi,
> 
> It's just a gentle reminder to review this patch.

Looks like this was either dropped, or didn't make it into my queue.

It's on the list now, I will deal with it soon.

> > diff --git a/drivers/mfd/stm32-timers.c b/drivers/mfd/stm32-timers.c
> > index add6033..44ed2fc 100644
> > --- a/drivers/mfd/stm32-timers.c
> > +++ b/drivers/mfd/stm32-timers.c
> > @@ -158,13 +158,18 @@ static const struct regmap_config stm32_timers_regmap_cfg = {
> >  
> >  static void stm32_timers_get_arr_size(struct stm32_timers *ddata)
> >  {
> > +	u32 arr;
> > +
> > +	/* Backup ARR to restore it after getting the maximum value */
> > +	regmap_read(ddata->regmap, TIM_ARR, &arr);
> > +
> >  	/*
> >  	 * Only the available bits will be written so when readback
> >  	 * we get the maximum value of auto reload register
> >  	 */
> >  	regmap_write(ddata->regmap, TIM_ARR, ~0L);
> >  	regmap_read(ddata->regmap, TIM_ARR, &ddata->max_arr);
> > -	regmap_write(ddata->regmap, TIM_ARR, 0x0);
> > +	regmap_write(ddata->regmap, TIM_ARR, arr);
> >  }
> >  
> >  static int stm32_timers_dma_probe(struct device *dev,
> > 

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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