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

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Date:   Fri, 24 Sep 2021 15:04:00 +0000
From:   Adam Thomson <Adam.Thomson.Opensource@...semi.com>
To:     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 21 September 2021 06:34, Alexandre Ghiti wrote:

> The SiFive Unmatched board uses the da9063 PMIC for reset: add a restart
> notifier that will execute a small i2c sequence allowing to reset the
> board.
> 
> The original implementation comes from Marcus Comstedt and Anders
> Montonen
> (https://forums.sifive.com/t/reboot-command/4721/28).
> 
> Signed-off-by: Alexandre Ghiti <alexandre.ghiti@...onical.com>
> ---
>  drivers/mfd/da9063-core.c       | 25 +++++++++++++++++++++++++
>  include/linux/mfd/da9063/core.h |  3 +++
>  2 files changed, 28 insertions(+)
> 
> diff --git a/drivers/mfd/da9063-core.c b/drivers/mfd/da9063-core.c
> index df407c3afce3..c87b8d611f20 100644
> --- a/drivers/mfd/da9063-core.c
> +++ b/drivers/mfd/da9063-core.c
> @@ -20,6 +20,7 @@
>  #include <linux/mutex.h>
>  #include <linux/mfd/core.h>
>  #include <linux/regmap.h>
> +#include <linux/reboot.h>
> 
>  #include <linux/mfd/da9063/core.h>
>  #include <linux/mfd/da9063/registers.h>
> @@ -158,6 +159,18 @@ static int da9063_clear_fault_log(struct da9063 *da9063)
>  	return ret;
>  }
> 
> +static int da9063_restart_notify(struct notifier_block *this,
> +				 unsigned long mode, void *cmd)
> +{
> +	struct da9063 *da9063 = container_of(this, struct da9063,
> restart_handler);
> +
> +	regmap_write(da9063->regmap, DA9063_REG_PAGE_CON, 0x00);
> +	regmap_write(da9063->regmap, DA9063_REG_CONTROL_F, 0x04);
> +	regmap_write(da9063->regmap, DA9063_REG_CONTROL_A, 0x68);
> +
> +	return NOTIFY_DONE;
> +}

I will talk with our HW team to clarify, but this sequence looks to be very
specific to the needs of the platform in question which doesn't feel right to
me. As was mentioned on another thread as well, the watchdog driver already has
a restart function to reset the device (and thus the system), so I don't believe
we should have multiple of these.

For board specific sequences, there are machine quirks I believe which can be
used to handle stuff like this, if this really isn't a generic solution to fit
all cases.