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

Lee Jones
2021-03-22T13:11:37Z

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@foss.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
Follow Linaro: Facebook | Twitter | Blog