Re: [PATCH 0/4] rtc: pcf2127: add support for battery low voltage detection

[Marc Kleine-Budde]

Hello Alexandre,

can you pick up this patch? It has been tested by Stefan Kerkmann and
it's working for our use case.

regards,
Marc

On 11.03.2026 16:02:26, Hugo Villeneuve wrote:
> From: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
>
> Hello,
> this patch series adds support for battery low voltage detection configuration
> for RTC devicesm, with specifc changes targeted at the pcf2127/2131 devices.
>
> The origin of this patch goes back to the initial commit to add support for the
> PCF2131 device. On the PCF2131, the battery low voltage detection is disabled by
> default at the hardware level, contrary to the PCF2127 where it is enabled by
> default. Because of that, a lot of people are stuck with a PCF2131 RTC device
> using a battery backup, but unable to use it!
>
> A lot of people are writing to me in private emails to report this as a bug
> in the PCF2131 driver. Others (and me) have proposed to implement device tree
> properties to enable these functions, but this was rejected [1][2][3].
>
> It is important to note that some projects do not have the luxury to modify
> the bootloder to enable that function at boot, and for these having a DT
> property that could be put in a DT overlay would simplify a lot their life.
> Also having to rely on a userspace application to configure the RTC is also
> not ideal, as some projects use stock Debian distros (for example), and
> adding a new application to their repository is not trivial or easy.
>
> So as the next best thing, this patch aims to add what is missing in the driver,
> the ability to enable/disable the battery low voltage detection with ioctls,
> similarly to what is done with the BSM.
>
> This patch has been tested on a custom board with a PCF2131 and using my
> userspace application:
>
>     git clone -b batlow_param git@xxxxxxxxxxxxxxx:repos/hvrtc.git
>
> Thank you.
>
> Link: https://lore.kernel.org/linux-rtc/20190910143945.9364-1-bruno.thomsen@xxxxxxxxx/ [1]
> Link: https://lore.kernel.org/linux-rtc/20191211163354.GC1463890@xxxxxxxxx/ [2]
> Link: https://lore.kernel.org/linux-rtc/20230123170731.6064430c50f5fb7b484d8734@xxxxxxxxxxx/ [3]
>
> Hugo Villeneuve (4):
>   rtc: pcf2127: remove redundant break statement in switch-case
>   rtc: pcf2127: add pcf2127_pwrmng_get/set
>   rtc: add battery low voltage detection feature
>   rtc: pcf2127: support battery low voltage detection function
>
>  drivers/rtc/rtc-pcf2127.c | 94 ++++++++++++++++++++++++++++++---------
>  include/uapi/linux/rtc.h  |  7 ++-
>  2 files changed, 80 insertions(+), 21 deletions(-)
>
>
> base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f
> --
> 2.47.3
>
>

-- 
Pengutronix e.K.                 | Marc Kleine-Budde          |
Embedded Linux                   | https://www.pengutronix.de |
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