linux-kernel - RE: [PATCH v2 05/28] ACPICA: Hardware: Enable firmware waking vector for both 32-bit and 64-bit FACS.

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Date:	Fri, 26 Jun 2015 01:41:51 +0000
From:	"Zheng, Lv" <lv.zheng@...el.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
	"Brown, Len" <len.brown@...el.com>, Lv Zheng <zetalog@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"Moore, Robert" <robert.moore@...el.com>
Subject: RE: [PATCH v2 05/28] ACPICA: Hardware: Enable firmware waking
 vector for both 32-bit and 64-bit FACS.

Hi, Rafael

> From: Rafael J. Wysocki [mailto:rjw@...ysocki.net]
> Sent: Friday, June 26, 2015 9:41 AM
> 
> On Friday, June 26, 2015 12:51:39 AM Zheng, Lv wrote:
> > Hi, Rafael
> >
> > > From: Rafael J. Wysocki [mailto:rjw@...ysocki.net]
> > > Sent: Friday, June 26, 2015 8:44 AM
> > >
> > > On Thursday, June 25, 2015 12:43:39 AM Zheng, Lv wrote:
> > > > Hi, Rafael
> > > >
> > > > > From: Rafael J. Wysocki [mailto:rjw@...ysocki.net]
> > > > > Sent: Thursday, June 25, 2015 7:57 AM
> > > > >
> > >
> > > [cut]
> > >
> > > > > >
> > > > > > +/*******************************************************************************
> > > > > > + *
> > > > > > + * FUNCTION:    acpi_set_firmware_waking_vector
> > > > > > + *
> > > > > > + * PARAMETERS:  physical_address    - 32-bit physical address of ACPI real mode
> > > > > > + *                                    entry point
> > > > > > + *              physical_address64  - 64-bit physical address of ACPI protected
> > > > > > + *                                    entry point
> > > > > > + *
> > > > > > + * RETURN:      Status
> > > > > > + *
> > > > > > + * DESCRIPTION: Sets the firmware_waking_vector fields of the FACS
> > > > > > + *
> > > > > > + ******************************************************************************/
> > > > > > +
> > > > > > +acpi_status
> > > > > > +acpi_set_firmware_waking_vector(acpi_physical_address physical_address,
> > > > > > +				acpi_physical_address physical_address64)
> > > > >
> > > > > The question here is: Why does the host OS need to care about the second
> > > > > argument of this function that will always be 0?  Why didn't you keep the
> > > > > old header of acpi_set_firmware_waking_vector() as a one-argument function
> > > > > taking a u32 and why didn't you add something like
> > > > >
> > > > > acpi_status acpi_set_firmware_waking_vector_full(u32 real_mode_address,
> > > > > 					acpi_physical_address high_address)
> > > > >
> > > > > and why didn't you redefine acpi_set_firmware_waking_vector() as
> > > > >
> > > > > acpi_status acpi_set_firmware_waking_vector(u32 real_mode_address)
> > > > > {
> > > > > 	return acpi_set_firmware_waking_vector_full(real_mode_address, 0);
> > > > > }
> > > > >
> > > > > ?
> > > > >
> > > > > If you did that, there wouldn't be any need to touch the code in
> > > > > drivers/acpi/sleep.c and the arch headers, so can you please explain to me
> > > > > why *exactly* you didn't do that?
> > > >
> > > > Host OS can set non 0 address for both  real_mode_address and high_address to indicate that it can support both 32-bit and 64-
> bit
> > > resume environments.
> > > > So if a BIOS favors 32-bit resume environment, it can resume from here; if another BIOS favors 64-bit resume environment, it
> can
> > > resume from there.
> > > > And host OSes can be implemented using only 1 binary to work with both BIOSes.
> > >
> > > I'm not talking about that.
> > >
> > > It is fine to provide a *new* interface for the OSes that want to do that
> > > (if any), but *why* is that regarded as a good enough reason for essentially
> > > *removing* the old interface that Linux (and presumably other OSes too) have
> > > been using so far?
> >
> > Maybe we should ask Bob if we shall just provide a new interfaces for this
> > and keep the old ones?
> 
> Sure, we can talk to Bob about that.
> 
> > According to my understanding, there is no such example in the ACPICA upstream.
> 
> Even so, that doesn't necessarily mean it is be impossible.

Yes.

> 
> > Some xxxx_full functions are still pending for being merged by ACPICA upstream,
> > they are divergences for now.
> 
> And it looks like this particular case will become one more divergence of that
> kind.

OK.
I'll refine the interface change to eliminate the divergence.

> 
> > >
> > > We don't want to pass nonzero as high_address anyway, so why are we *forced* to
> > > make pointless changes to non-ACPICA code just to be able to always pass 0
> > > as high_address?
> >
> > IMO, OSPMs can do this if the cost is not high.
> > It seems by following your suggestion, we only need to do slight changes in sleep.c.
> 
> Which aren't necessary, right?  And they don't really make things any better.
> 
> So I don't see a reason to make them.

Yes.
If this is done in ACPICA, sleep.c needn't be changed.

Thanks and best regards
-Lv