[PATCH v3 0/4] rtc: stm32: add pinctrl interface to handle RTC outs

[Valentin Caron <valentin.caron@foss.st.com>]

This series adds a pinctrl/pinmux interface to control STM32 RTC outputs.

Theses two signals output are possible:
 - LSCO (Low Speed Clock Output) that allow to output LSE clock on a pin.
   On STM32MPU Discovery boards, this feature is used to generate a clock
   to Wifi/Bluetooth module.
 - Alarm out that allow to send a pulse on a pin when alarm A of the RTC
   expires.

First attempt [1] was based on 'st,' vendor properties, this one is based
on pinctrl and pinmux framework.

As device-trees will be upstreamed separately, here is an example:

stm32-pinctrl {
    rtc_rsvd_pins_a: rtc-rsvd-0 {
        pins {
            pinmux = <STM32_PINMUX('B', 2, AF1)>, /* OUT2 */
                     <STM32_PINMUX('I', 8, ANALOG)>; /* OUT2_RMP */
        };
    };
};

stm32-rtc {
    pinctrl-0 = <&rtc_rsvd_pins_a &rtc_alarma_pins_a>;

    /* Enable by foo-device */
    rtc_lsco_pins_a: rtc-lsco-0 {
        pins = "out2_rmp";
        function = "lsco";
    };

    /* Enable by stm32-rtc hog */
    rtc_alarma_pins_a: rtc-alarma-0 {
        pins = "out2";
        function = "alarm-a";
    };
};

foo-device {
    pinctrl-0 = <&rtc_lsco_pins_a>;
};

[1] https://lore.kernel.org/linux-arm-kernel/20220504130617.331290-5-valentin.caron@foss.st.com/t/#m37935e92315e22bbe085775096175afc05b7ff09

Since v2:
 - Modify Kconfig after (a lot of) robots alert:
     + https://lore.kernel.org/oe-kbuild-all/202407190654.I3RI7WfP-lkp@intel.com/
     + https://lore.kernel.org/oe-kbuild-all/202407191258.1oitwwMV-lkp@intel.com/
     + https://lore.kernel.org/oe-kbuild-all/202407200400.NnW2fJ0q-lkp@intel.com/
     + https://lore.kernel.org/oe-kbuild-all/202407181525.BRNKqmNf-lkp@intel.com/
     + https://lore.kernel.org/oe-kbuild-all/202407191830.8bh5dJ09-lkp@intel.com/
   Make RTC_DRV_STM32 depends on OF, PINCTRL and COMMON_CLK as they are menuconfig entry.
   Make RTC_DRV_STM32 select PINCONF, PINCONF_GENERIC and PINMUX as they config entry.
   
Since v1:
 - Select PINMUX and PINCONF_GENERIC to solve:
   https://lore.kernel.org/oe-kbuild-all/202407130943.ie6n2Orh-lkp@intel.com/
 - Make stm32_rtc_pinctrl_pins as static to solve:
   https://lore.kernel.org/oe-kbuild-all/202407130612.OEicZbNE-lkp@intel.com/
 - Change "depends on" to "select" COMMON_CLK config
 - Modify regex in dt-binding to avoid properties like "rtc--123" as valid ones.

Valentin Caron (4):
  dt-bindings: rtc: stm32: describe pinmux nodes
  rtc: stm32: add pinctrl and pinmux interfaces
  rtc: stm32: add Low Speed Clock Output (LSCO) support
  rtc: stm32: add alarm A out feature

 .../devicetree/bindings/rtc/st,stm32-rtc.yaml |  28 ++
 drivers/rtc/Kconfig                           |   6 +
 drivers/rtc/rtc-stm32.c                       | 281 ++++++++++++++++++
 3 files changed, 315 insertions(+)

-- 
2.25.1