Re: [PATCH] Default to ACPI reboots on newish X86 hardware

[Len Brown <lenb@kernel.org>]

On Thu, 7 Jan 2010, Christian Hofstaedtler wrote:

Thanks for writing this patch Christian,
it is something that has been unsettled for
a long time and it will be great to close the issue.

> Newer hardware is assumed to no longer reboot succesfully using the
> keyboard controller, but needs to use ACPI instead.
> To not cause problems with older hardware, only hardware with a BIOS
> date 2006 or newer is considered for this choice. Broken BIOSes
> reporting a BIOS date of 0 are not specially considered, and therefore
> get the KBD reboot behaviour.
> 
> Also unifiy reboot_type selection code.

Please split the patch in two patches:

1. cleanup w/o policy change
2. policy change w/o cleanup

better if the policy change is #2, so if we need to revert it
we don't have to revert the cleanup too.

> Signed-off-by: Christian Hofstaedtler <ch@zeha.at>
> ---
>  arch/x86/include/asm/emergency-restart.h |    1 +
>  arch/x86/kernel/reboot.c                 |   65 ++++++++++++++++++++++++------
>  2 files changed, 53 insertions(+), 13 deletions(-)


> +/* See if the Hardware is new enough to support ACPI reboots. */
> +static int __init reboot_acpi_likey_supported(void)
> +{
> +        int year;
> +
> +	/* Doesn't exist? Likely an old system */
> +	if (!dmi_get_date(DMI_BIOS_DATE, &year, NULL, NULL)) {
> +		return 0;
> +	}

I think it may be better to simply return 1 in this case.

While we have seen dmi_get_date() fail in practice on "modern" machines,
if CONFIG_ACPI_BLACKLIST_YEAR is set, we will already punish users by
disabling ACPI and making them invoke acpi=force.

So the effect of this check is to disable ACPI-reset
on systems where the user has likely already invoked acpi=force --
which seems somewhat counter-intuitive.

> +        /* 2006 was decided as the cut-off year. */
> +	if (year < 2006) {
> +		return 0;
> +	}

I'd rather see 2003.
If we run into trouble, it is a 1-liner to move it forward.
But I think we'll probably do fine with anything newer than 2001.

thanks,
Len Brown, Intel Open Source Technolgy Center