linux-kernel - Re: [PATCH] x86: honor ACPI FADT flag indicating absence of a CMOS RTC

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Date:	Fri, 18 Oct 2013 08:29:08 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Jan Beulich <JBeulich@...e.com>,
	John Stultz <john.stultz@...aro.org>
Cc:	mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: honor ACPI FADT flag indicating absence of a CMOS
 RTC


* Jan Beulich <JBeulich@...e.com> wrote:

> We shouldn't be creating a corresponding platform device in that case.

There's a sad lack of context in the changelog, how was it found, does 
this address any problem/bug observed in practice, etc?

> Signed-off-by: Jan Beulich <jbeulich@...e.com>
> 
> ---
>  arch/x86/kernel/rtc.c |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> --- 3.12-rc5/arch/x86/kernel/rtc.c
> +++ 3.12-rc5-x86-ACPI-no-RTC/arch/x86/kernel/rtc.c
> @@ -192,6 +192,11 @@ static __init int add_rtc_cmos(void)
>  	if (mrst_identify_cpu())
>  		return -ENODEV;
>  
> +#ifdef CONFIG_ACPI
> +	if (acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_CMOS_RTC)
> +		return -ENODEV;
> +#endif

It might also be prudent to emit a KERN_INFO line telling that we don't 
create the device - so that people who suddenly see unexpected breakage or 
change in behavior have a chance to see what we've done?

Thanks,

	Ingo
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