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Commit 84e3ffb5 authored by Fabrice Gasnier's avatar Fabrice Gasnier Committed by Greg Kroah-Hartman
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mfd: stm32-timers: Avoid clearing auto reload register 



[ Upstream commit 4917e498c6894ba077867aff78f82cffd5ffbb5c ]

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: d0f949e2 ("mfd: Add STM32 Timers driver")
Signed-off-by: default avatarFabrice Gasnier <fabrice.gasnier@foss.st.com>
Acked-by: default avatarWilliam Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: default avatarLee Jones <lee.jones@linaro.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent ff5042f0

drivers/mfd/stm32-timers.c

+6 −1
Original line number Diff line number Diff line
@@ -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 void stm32_timers_dma_probe(struct device *dev,