linux-kernel - Re: [PATCH 3/6] ARM: PSCI: Register with kernel restart handler

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Date:	Wed, 13 Apr 2016 12:05:19 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Russell King <linux@....linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Wolfram Sang <wsa@...-dreams.de>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: Re: [PATCH 3/6] ARM: PSCI: Register with kernel restart handler

On Fri, Apr 08, 2016 at 05:53:56AM -0700, Guenter Roeck wrote:
> Register with kernel restart handler instead of setting arm_pm_restart
> directly. This enables support for replacing the PSCI restart handler
> with a different handler if necessary for a specific board.
> 
> Select a priority of 129 to indicate a higher than default priority, but
> keep it as low as possible since PSCI reset is known to fail on some
> boards.

For reference, which boards?

It's unfortunate that that a PSCI 0.2+ implementation would be lacking a
working SYSTEM_RESET implementation, and it's certainly a mistake to
discourage.

> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> ---
> It might make sense to introduce a restart-priority property for devicetree
> based configurations, but I am not sure if this would be acceptable.

>From the DT side, I'm not keen on properties for priorities. They're
incredibly fragile and don't really encode a HW property.

A better option would be to have a property to describe how the PSCI
implementation is broken (e.g. broken-system-reset), and not register
the handler at all in that case.

Thanks,
Mark.

>  drivers/firmware/psci.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/firmware/psci.c b/drivers/firmware/psci.c
> index 11bfee8b79a9..99fab3ac3fd5 100644
> --- a/drivers/firmware/psci.c
> +++ b/drivers/firmware/psci.c
> @@ -231,11 +231,18 @@ static int get_set_conduit_method(struct device_node *np)
>  	return 0;
>  }
>  
> -static void psci_sys_reset(enum reboot_mode reboot_mode, const char *cmd)
> +static int psci_sys_reset(struct notifier_block *np, unsigned long action,
> +			  void *data)
>  {
>  	invoke_psci_fn(PSCI_0_2_FN_SYSTEM_RESET, 0, 0, 0);
> +	return NOTIFY_DONE;
>  }
>  
> +static struct notifier_block psci_sys_reset_nb = {
> +	.notifier_call = psci_sys_reset,
> +	.priority = 129,
> +};
> +
>  static void psci_sys_poweroff(void)
>  {
>  	invoke_psci_fn(PSCI_0_2_FN_SYSTEM_OFF, 0, 0, 0);
> @@ -461,7 +468,7 @@ static void __init psci_0_2_set_functions(void)
>  
>  	psci_ops.migrate_info_type = psci_migrate_info_type;
>  
> -	arm_pm_restart = psci_sys_reset;
> +	register_restart_handler(&psci_sys_reset_nb);
>  
>  	pm_power_off = psci_sys_poweroff;
>  }
> -- 
> 2.5.0
>