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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Message-ID: <1AE640813FDE7649BE1B193DEA596E8802734087@SHSMSX101.ccr.corp.intel.com>
Date:	Fri, 26 Jun 2015 00:51:39 +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 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?
According to my understanding, there is no such example in the ACPICA upstream.
Some xxxx_full functions are still pending for being merged by ACPICA upstream, they are divergences for now.

> 
> 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.

Thanks and best regards
-Lv