linux-kernel - Re: [PATCH] x86: force HPET to immediately enable RTC wake

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Date:	Wed, 19 Oct 2011 23:37:27 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Mark Langsdorf <mark.langsdorf@....com>
Cc:	venki@...gle.com, linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86: force HPET to immediately enable RTC wake

CCing x86 people.

On Wed, Oct 19, 2011 at 12:26:48PM -0500, Mark Langsdorf wrote:
> When HPET is operating in RTC mode, the TN_ENABLE bit
> on timer1 controls whether the HPET or the RTC delivers
> interrupts to irq8. When the system goes into suspend,
> the RTC driver sends a signal to the HPET driver so
> that the HPET releases control of irq8, allowing the
> RTC to wake the system from suspend. The switchover
> is accomplished by a write to the HPET configuration
> registers which currently only occurs while servicing
> the HPET interrupt.
> 
> On some systems, I have seen the system suspend before
> an HPET interrupt occurs, preventing the write to the
> HPET configuration register and leaving the HPET in
> control of the irq8. As the HPET is not active during
> suspend, it does not generate a wake signal and RTC
> alarms do not work.
> 
> This patch forces the HPET driver to immediately transfer
> control of the irq8 channel to the RTC instead of waiting
> until the next interrupt event.
> 
> Signed-off-by: Mark Langsdorf <mark.langsdorf@....com>
> Tested-by: Andreas Herrmann <andreas.herrmann3@....com>
> ---
>  arch/x86/kernel/hpet.c |   21 ++++++++++++++-------
>  1 files changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
> index 4aecc54..10b09d7 100644
> --- a/arch/x86/kernel/hpet.c
> +++ b/arch/x86/kernel/hpet.c
> @@ -1048,6 +1048,14 @@ int hpet_rtc_timer_init(void)
>  }
>  EXPORT_SYMBOL_GPL(hpet_rtc_timer_init);
>  
> +static void hpet_disable_rtc_channel(void)
> +{
> +	unsigned long cfg;
> +	cfg = hpet_readl(HPET_T1_CFG);
> +	cfg &= ~HPET_TN_ENABLE;
> +	hpet_writel(cfg, HPET_T1_CFG);
> +}
> +
>  /*
>   * The functions below are called from rtc driver.
>   * Return 0 if HPET is not being used.
> @@ -1059,6 +1067,9 @@ int hpet_mask_rtc_irq_bit(unsigned long bit_mask)
>  		return 0;
>  
>  	hpet_rtc_flags &= ~bit_mask;
> +	if (unlikely(!hpet_rtc_flags))
> +		hpet_disable_rtc_channel();
> +
>  	return 1;
>  }
>  EXPORT_SYMBOL_GPL(hpet_mask_rtc_irq_bit);
> @@ -1124,15 +1135,11 @@ EXPORT_SYMBOL_GPL(hpet_rtc_dropped_irq);
>  
>  static void hpet_rtc_timer_reinit(void)
>  {
> -	unsigned int cfg, delta;
> +	unsigned int delta;
>  	int lost_ints = -1;
>  
> -	if (unlikely(!hpet_rtc_flags)) {
> -		cfg = hpet_readl(HPET_T1_CFG);
> -		cfg &= ~HPET_TN_ENABLE;
> -		hpet_writel(cfg, HPET_T1_CFG);
> -		return;
> -	}
> +	if (unlikely(!hpet_rtc_flags))
> +		hpet_disable_rtc_channel();
>  
>  	if (!(hpet_rtc_flags & RTC_PIE) || hpet_pie_limit)
>  		delta = hpet_default_delta;
> 
> --
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-- 
Regards/Gruss,
    Boris.
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