Re: Why don't we use _TTS method?

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Friday, 4 May 2007 20:10, Moore, Robert wrote:
> "New" is of course relative. In the ACPI world, anything about ACPI 3.0
> is still considered "new". Windows has yet to fully implement ACPI 2.0,
> let alone ACPI 3.0...
> 
> Please point me to where the "spec spec seems to suggest that _GTS
> should be executed with interrupts off", as I don't think it should.

The ACPI 2.0 specification, 7.3.3, says:

"OSPM will set the sleep enable (SLP_EN) bit in the PM1 control register
immediately following the execution of the _GTS control method without
performing any other physical I/O or allowing any interrupt servicing."

This is also clearly stated in Subsection 9.1.

Yet, according to the same specification, 9.1.6:

"7. OSPM executes the _GTS control method, passing an argument that indicates
    the sleeping state to be entered (1, 2, 3, or 4 representing S1, S2, S3, and
    S4).
8. OSPM clears the WAK_STS in the PM1a_STS and PM1b_STS registers.
9. OSPM saves the local processor’s context to memory.
10. OSPM flushes caches (only if entering S1, S2 or S3).
11. OSPM sets GPE enable registers to ensure that all appropriate wake signals are armed.
12. If entering an S4 state using the S4BIOS mechanism, OSPM writes the
    S4BIOS_REQ value (from the FADT) to the SMI_CMD port. This passes control
    to the BIOS, which then transitions the platform into the S4BIOS state.
13. If not entering an S4BIOS state, then OSPM writes SLP_TYPa (from the
    associated sleeping object) with the SLP_ENa bit set to the PM1a_CNT
    register.
14. OSPM writes SLP_TYPb with the SLP_EN bit set to the PM1b_CNT register."

which kind of contradicts the previous requirement.  Still, 8-14 look like
things that should be done with interrupts off.

> In any case, the AML interpreter cannot be executed with interrupts off.
> There is way too much going on in that code.

Well, perhaps we can execute _GTS immediately before switching interrupts off.

Greetings,
Rafael


> > -----Original Message-----
> > From: Rafael J. Wysocki [mailto:rjw@sisk.pl]
> > Sent: Friday, May 04, 2007 1:51 AM
> > To: Alexey Starikovskiy
> > Cc: Moore, Robert; ACPI Devel Maling List; pm list; Pavel Machek
> > Subject: Re: Why don't we use _TTS method?
> > 
> > Hi Alexey,
> > 
> > On Friday, 4 May 2007 06:34, Alexey Starikovskiy wrote:
> > > Rafael,
> > >
> > > code in prepare() and enter() is split as code with interrupts on
> and
> > > code with interrupts off.
> > 
> > I see.  Still, the spec seems to suggest that _GTS should be executed
> with
> > interrupts off, but we run it in the 'interrupts on' part of code.
> Isn't
> > that
> > wrong?
> > 
> > > thus it doesn't quite follow a spec in regards of driver suspend.
> > 
> > Yes.
> > 
> > > Basically we need to either split it to smaller pieces or have hooks
> > > to control interrupts/driver suspend from this code.
> > 
> > I'd like to split it and I'd like to figure out *how* to do this.
> More
> > precisely, I'd like to learn which part of acpi_pm_prepare() should be
> > executed before device_suspend() and which part can be run after it.
> > Analogously, I'd like to learn which part of acpi_pm_finish() needs to
> be
> > run before device_resume() and which part can be (or should be) run
> > after it.
> > 
> > Greetings,
> > Rafael
> > 
> > 
> > > On 5/4/07, Rafael J. Wysocki <rjw@sisk.pl> wrote:
> > > > On Friday, 4 May 2007 00:57, Moore, Robert wrote:
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: linux-acpi-owner@vger.kernel.org [mailto:linux-acpi-
> > > > > > owner@vger.kernel.org] On Behalf Of Rafael J. Wysocki
> > > > > > Sent: Thursday, May 03, 2007 1:02 PM
> > > > > > To: ACPI Devel Maling List
> > > > > > Cc: pm list; Pavel Machek
> > > > > > Subject: Why don't we use _TTS method?
> > > > > >
> > > > > > Hi,
> > > > > >
> > > > > > I've got two questions regarding the implementation of the
> ACPI
> > > > > > poweroff/sleep
> > > > > > code in drivers/acpi/sleep and drivers/acpi/hardware .
> > > > > >
> > > > > > 1) We don't seem to use the _TTS system-control method,
> although
> > the
> > > > > ACPI
> > > > > > specification (ACPI 3.0b) says that this method should be used
> for
> > > > > > intiating
> > > > > > and finishing power transitions.  Could you please tell me why
> we
> > > > > don't
> > > > > > use it?
> > > > > >
> > > > > [Moore, Robert]
> > > > >
> > > > > Probably because it's fairly new and it takes a long time for
> these
> > > > > things to appear in real machines. Also, needs to be supported
> in
> > > > > Windows before we ever see it in real machines.
> > > >
> > > > Hmm, it already was in the 3.0 spec from 2004, so it doesn't seem
> to
> > be
> > > > that new.  Still, I'm not an expert ...
> > > >
> > > > > > 2) In the functions acpi_enter_sleep_state_prep(),
> > > > > > acpi_enter_sleep_state(),
> > > > > > acpi_leave_sleep_state() we manipulate GPEs quite extensively
> (we
> > > > > disable
> > > > > > and enable them for a couple of times during a transition),
> > although
> > > > > the
> > > > > > specification doesn't tell anything about that explicitly.
> Could
> > you
> > > > > > please
> > > > > > explain to me what the purpose of that is?
> > > > > >
> > > > > [Moore, Robert]
> > > > >
> > > > > There a wake GPEs and runtime GPEs that need to be managed
> > separately.
> > > > > We want to make sure that only the "Wake" GPEs are enabled as we
> > goto
> > > > > sleep.
> > > >
> > > > I understand that, but the runtime GPEs seem to be disabled before
> we
> > call
> > > > device drivers' .suspend() routines (ie. before the devices are
> placed
> > in the
> > > > appropriate Dx states) and that's the point I don't quite get.  Is
> > there a
> > > > technical reason for doing it in this particular place?
> > > >
> > > > Thanks a lot for your reply.
> > > >
> > > > Greetings,
> > > > Rafael
> > > > -
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> > >
> > >
> > 
> > --
> > If you don't have the time to read,
> > you don't have the time or the tools to write.
> > 		- Stephen King
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