linux-kernel - RE: [PATCH] drivers: mfd: da9063: Add restart notifier implementation

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Date:   Thu, 30 Sep 2021 09:28:37 +0000
From:   Adam Thomson <Adam.Thomson.Opensource@...semi.com>
To:     David Abdurachmanov <david.abdurachmanov@...il.com>,
        Adam Thomson <Adam.Thomson.Opensource@...semi.com>
CC:     Alexandre Ghiti <alexandre.ghiti@...onical.com>,
        Support Opensource <Support.Opensource@...semi.com>,
        Lee Jones <lee.jones@...aro.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] drivers: mfd: da9063: Add restart notifier implementation

On 30 September 2021 08:51, David Abdurachmanov wrote:

> > Regardless of this though, the consensus right now would be to use the RTC as
> a
> > wake event to restart the platform. An alarm can be set for a couple of seconds
> > into the future (or longer if required) and that would provide the event
> > required to come up from powerdown/shutdown, in the absence of
> AUTOBOOT being
> > set in OTP. I believe this would be the safest route to take in this case. You
> > can then just use the SHUTDOWN bit on CONTROL_F to take down the board.
> 
> Today I was looking into OpenBSD DA9063 drivers and they might be
> doing what you described for the reset.
> 
> dev/fdt/dapmic.c
> 
> [..]
> 241 void
> 242 dapmic_reset(void)
> 243 {
> 244     struct dapmic_softc *sc = dapmic_cd.cd_devs[0];
> 245     uint8_t reg;
> 246
> 247     /* Enable tick alarm wakeup with a one second interval. */
> 248     reg = dapmic_reg_read(sc, ALARM_MO);
> 249     reg &= ~ALARM_MO_TICK_TYPE;
> 250     reg |= ALARM_MO_TICK_WAKE;
> 251     dapmic_reg_write(sc, ALARM_MO, reg);
> 252
> 253     /* Enable tick function. */
> 254     reg = dapmic_reg_read(sc, ALARM_Y);
> 255     reg |= ALARM_Y_TICK_ON;
> 256     dapmic_reg_write(sc, ALARM_Y, reg);
> 257
> 258     /* Clear events such that we wake up again. */
> 259     dapmic_reg_write(sc, EVENT_A, dapmic_reg_read(sc, EVENT_A));
> 260     dapmic_reg_write(sc, CONTROL_F, CONTROL_F_SHUTDOWN);
> 261 }
> [..]

This is using the tick alarm which is repeating. That is one option or
alternatively there's a one-shot alarm option which can be used which might be
preferable as you won't see continues events from the RTC when the system boots
up again.