rtc: ds1685: Fix bank switching to avoid endless loop

ds1685_rtc_begin_data_access() tried to access an extended register before
enabling access to it by switching to bank 1. Depending on content in NVRAM
this could lead to an endless loop. While at it fix also switch back to
bank 0 in ds1685_rtc_end_data_access().

Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
---
 drivers/rtc/rtc-ds1685.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

On 9/10/2020 04:41, Thomas Bogendoerfer wrote:
> ds1685_rtc_begin_data_access() tried to access an extended register before
> enabling access to it by switching to bank 1. Depending on content in NVRAM
> this could lead to an endless loop. While at it fix also switch back to
> bank 0 in ds1685_rtc_end_data_access().
> 
> Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> ---
>  drivers/rtc/rtc-ds1685.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/rtc/rtc-ds1685.c b/drivers/rtc/rtc-ds1685.c
> index 56c670af2e50..dfbd7b88b2b9 100644
> --- a/drivers/rtc/rtc-ds1685.c
> +++ b/drivers/rtc/rtc-ds1685.c
> @@ -193,12 +193,12 @@ ds1685_rtc_begin_data_access(struct ds1685_priv *rtc)
>  	rtc->write(rtc, RTC_CTRL_B,
>  		   (rtc->read(rtc, RTC_CTRL_B) | RTC_CTRL_B_SET));
>  
> +	/* Switch to Bank 1 */
> +	ds1685_rtc_switch_to_bank1(rtc);
> +
>  	/* Read Ext Ctrl 4A and check the INCR bit to avoid a lockout. */
>  	while (rtc->read(rtc, RTC_EXT_CTRL_4A) & RTC_CTRL_4A_INCR)
>  		cpu_relax();
> -
> -	/* Switch to Bank 1 */
> -	ds1685_rtc_switch_to_bank1(rtc);
>  }
>  
>  /**
> @@ -213,7 +213,7 @@ static inline void
>  ds1685_rtc_end_data_access(struct ds1685_priv *rtc)
>  {
>  	/* Switch back to Bank 0 */
> -	ds1685_rtc_switch_to_bank1(rtc);
> +	ds1685_rtc_switch_to_bank0(rtc);
>  
>  	/* Clear the SET bit in Ctrl B */
>  	rtc->write(rtc, RTC_CTRL_B,
> 

This probably needs to be sent to stable as well.

Acked-by: Joshua Kinard <kumba@gentoo.org>

On Thu, 10 Sep 2020 10:41:24 +0200, Thomas Bogendoerfer wrote:
> ds1685_rtc_begin_data_access() tried to access an extended register before
> enabling access to it by switching to bank 1. Depending on content in NVRAM
> this could lead to an endless loop. While at it fix also switch back to
> bank 0 in ds1685_rtc_end_data_access().

Applied, thanks!

[1/1] rtc: ds1685: Fix bank switching to avoid endless loop
      commit: 9f8010e71f091b0609452742cfed4650ee633c44

Best regards,