From mboxrd@z Thu Jan  1 00:00:00 1970
From: yakui_zhao <yakui.zhao@intel.com>
Subject: Re: [PATCH 1/2] ACPICA: Clear power button status before enabling
	event
Date: Thu, 18 Jun 2009 10:14:26 +0800
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To: Bjorn Helgaas <bjorn.helgaas@hp.com>
Cc: Len Brown <lenb@kernel.org>, "linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>, "Moore, Robert" <robert.moore@intel.com>

On Thu, 2009-06-18 at 03:08 +0800, Bjorn Helgaas wrote:
> On Wednesday 17 June 2009 01:34:38 am yakui_zhao wrote:
> > On Wed, 2009-06-17 at 12:26 +0800, Bjorn Helgaas wrote:
> > > On Tuesday 16 June 2009 9:21:40 pm yakui_zhao wrote:
> > > > On Tue, 2009-06-16 at 00:49 +0800, Bjorn Helgaas wrote:
> > > > > Clear power button status before enabling event.
> > > > > 
> > > > > It's unusual to enable an event, then immediately clear it, so this
> > > > > looks like a possible bug.  If it was intentional, perhaps a comment
> > > > > would be in order.
> > > > IMO this patch is unnecessary.
> > > 
> > > > It seems that we will clear the power button event immediately after it
> > > > is resumed from OS. (This is done in the function of
> > > > acpi_suspend_enter).
> > > 
> > > A comment in acpi_suspend_enter() refers to ACPI 3.0b sec. 4.7.2.2.1.1,
> > > which says "OSPM responds [to a button press after the button press that
> > > transitioned the system into a sleeping state] by clearing the power button
> > > status bit and waking the system."
> > If the power button event is not cleared after finishing the resume, the
> > acpid will receive the power button event and then power off the system.
> > So OSPM had better clear the power button event in course of resuming to
> > avoid that the box is poweroff.
> 
> I agree.
> 
> > > So *somebody* has to clear the status bit, but I'm not sure that it has
> > > to be done in the Linux-specific code, e.g,. acpi_suspend_enter().  The
> > > term "OSPM" seems broad enough to include both the ACPI CA and the Linux-
> > > specific code, and it may be more robust to clear it in the CA.
> > > 
> > > > Maybe the power event status bit is set before we re-enable the event
> > > > bit. And after we re-enable the power button event, OS can handle the
> > > > power button event (the acpi_leave_sleep_state is called with interrupts
> > > > enabled). 
> > > > 
> > > > If the patch is applied, the power button event will be lost.
> > > 
> > > I think this is the scenario you refer to:
> > > 
> > >   button press A causes wakeup
> > >   <possible button press B>
> > >   acpi_suspend_enter() clears event
> > >   <possible button press C>
>       acpi_leave_sleep_state() runs _WAK here
> > >   acpi_leave_sleep_state() clears event
> > >   acpi_leave_sleep_state() enables event
> > >   <possible button press D>
> > > 
> > > Even without this patch, we would lose button event B.  With this patch,
> > > we would also lose button event C.  This whole sequence should take very
> > > little time, so I'm dubious that there is any value in keeping either
> > > B or C -- it seems they'd most likely be unintentional.
> > Without this patch, the power button event C can be handled.
> > 
> > If the power button event bit will be set in the _WAK object, then this
> > event can't be handled after applying your patch.
> 
> I agree (because we run _WAK before clearing the power button event).
> 
> > > Actually, it seems like it would make the most sense to apply this patch
> > > *and* stop clearing the event in acpi_suspend_enter().  Then the code is
> > > simpler and easier to analyze, because we only touch the button status in
> > > one place.
> > IMO it will be better to clear the power button event in the function of
> > acpi_suspend_enter.
> > If we don't do that, maybe the BIOS will set the power button event
> > status/enable bit. And after the interrupt is enabled, the power button
> > event handler will send the event. In such case the acpid will receive
> > the event. Maybe the box will be powered off after resuming. This is not
> > what we wanted.
> 
> I agree.
> 
> What's your opinion of the following patch?  This drops the clear
> from acpi_suspend_enter().  In the ACPI CA acpi_leave_sleep_state(),
> it clears first, then enables, and moves both before the _WAK
> execution.
> 
>   button press A causes wakeup
>   <possible button press (or BIOS sets event) B>
>   acpi_leave_sleep_state() clears all GPEs
>   acpi_leave_sleep_state() enables runtime GPEs
>   acpi_leave_sleep_state() clears power button event
>   <possible button press C>
>   acpi_leave_sleep_state() enables power button event
>   <possible button press D>
>   acpi_leave_sleep_state() runs _WAK
>   <possible button "press" E from _WAK>
>   <possible button press F>
>   
> This should work the same as the current code -- we drop event B
> as desired, and we handle all others.
> 
> It has the advantages that we remove a bit of code from Linux/ACPI,
> we only touch the power button events in one place, and we follow
> the same pattern (clear, then enable) as the GPEs.
> 
> I'm not sure why acpi_suspend_enter() only clears the event when
> the acpi_target_sleep_state == ACPI_STATE_S3.  Sec. 4.7.2.2.1.1
> doesn't mention that.
We had better not delete the code that clears the power button event in
course of acpi_suspend_enter. 
This is to avoid that the power button wake event hits the user space.

Maybe the BIOS will set the power button event enable/status bit. And
after the interrupt is enabled, the power button event will hit the
userland. So it is appropriate to clear the power button event as early
as possible.
    Of course it can be cleared in the function of
"acpi_leave_sleep_state_prep". 
   In the following patch the power button event is cleared in the
function of acpi_leave_sleep_state, which is called with the interrupt
enabled.
   IMO this is not appropriate.

Thanks.
> 
> Bjorn
> 
> 
> diff --git a/drivers/acpi/acpica/hwsleep.c b/drivers/acpi/acpica/hwsleep.c
> index db307a3..c3252ee 100644
> --- a/drivers/acpi/acpica/hwsleep.c
> +++ b/drivers/acpi/acpica/hwsleep.c
> @@ -592,6 +592,18 @@ acpi_status acpi_leave_sleep_state(u8 sleep_state)
>  		return_ACPI_STATUS(status);
>  	}
>  
> +	/* Enable power button */
> +
> +	(void)
> +	    acpi_write_bit_register(acpi_gbl_fixed_event_info
> +			      [ACPI_EVENT_POWER_BUTTON].
> +			      status_register_id, ACPI_CLEAR_STATUS);
> +
> +	(void)
> +	    acpi_write_bit_register(acpi_gbl_fixed_event_info
> +			      [ACPI_EVENT_POWER_BUTTON].
> +			      enable_register_id, ACPI_ENABLE_EVENT);
> +
>  	arg.integer.value = sleep_state;
>  	status = acpi_evaluate_object(NULL, METHOD_NAME__WAK, &arg_list, NULL);
>  	if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
> @@ -608,18 +620,6 @@ acpi_status acpi_leave_sleep_state(u8 sleep_state)
>  
>  	acpi_gbl_system_awake_and_running = TRUE;
>  
> -	/* Enable power button */
> -
> -	(void)
> -	    acpi_write_bit_register(acpi_gbl_fixed_event_info
> -			      [ACPI_EVENT_POWER_BUTTON].
> -			      enable_register_id, ACPI_ENABLE_EVENT);
> -
> -	(void)
> -	    acpi_write_bit_register(acpi_gbl_fixed_event_info
> -			      [ACPI_EVENT_POWER_BUTTON].
> -			      status_register_id, ACPI_CLEAR_STATUS);
> -
>  	arg.integer.value = ACPI_SST_WORKING;
>  	status = acpi_evaluate_object(NULL, METHOD_NAME__SST, &arg_list, NULL);
>  	if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
> diff --git a/drivers/acpi/sleep.c b/drivers/acpi/sleep.c
> index 01574a0..b63c525 100644
> --- a/drivers/acpi/sleep.c
> +++ b/drivers/acpi/sleep.c
> @@ -257,13 +257,6 @@ static int acpi_suspend_enter(suspend_state_t pm_state)
>  	/* Reprogram control registers and execute _BFS */
>  	acpi_leave_sleep_state_prep(acpi_state);
>  
> -	/* ACPI 3.0 specs (P62) says that it's the responsibility
> -	 * of the OSPM to clear the status bit [ implying that the
> -	 * POWER_BUTTON event should not reach userspace ]
> -	 */
> -	if (ACPI_SUCCESS(status) && (acpi_state == ACPI_STATE_S3))
> -		acpi_clear_event(ACPI_EVENT_POWER_BUTTON);
> -
>  	/*
>  	 * Disable and clear GPE status before interrupt is enabled. Some GPEs
>  	 * (like wakeup GPE) haven't handler, this can avoid such GPE misfire.
> --
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