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

Fabrice Gasnier
2021-03-22T11:00:11Z

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.

Best Regards,
Fabrice

>
> 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,
>