linux-kernel - RE: [PATCH] x86/ACPI/cstate: Allow ACPI C1 FFH MWAIT use on AMD systems

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Message-ID: <BN6PR1201MB0131CA87635E77604CE1FDE1F8FE0@BN6PR1201MB0131.namprd12.prod.outlook.com>
Date:   Wed, 24 May 2017 18:16:05 +0000
From:   "Ghannam, Yazen" <Yazen.Ghannam@....com>
To:     Pavel Machek <pavel@....cz>
CC:     "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "len.brown@...el.com" <len.brown@...el.com>
Subject: RE: [PATCH] x86/ACPI/cstate: Allow ACPI C1 FFH MWAIT use on AMD
 systems

> -----Original Message-----
> From: Pavel Machek [mailto:pavel@....cz]
> Sent: Tuesday, May 23, 2017 8:25 AM
> To: Ghannam, Yazen <Yazen.Ghannam@....com>
> Cc: linux-pm@...r.kernel.org; x86@...nel.org; linux-
> kernel@...r.kernel.org; rjw@...ysocki.net; len.brown@...el.com
> Subject: Re: [PATCH] x86/ACPI/cstate: Allow ACPI C1 FFH MWAIT use on
> AMD systems
> 
> On Wed 2017-05-17 09:20:19, Yazen Ghannam wrote:
> > From: Yazen Ghannam <yazen.ghannam@....com>
> >
> > AMD systems support the Monitor/Mwait instructions and these can be
> > used for ACPI C1 in the same way as on Intel systems, with appropriate
> > BIOS support.
> >
> > Allow ffh_cstate_init() to succeed on AMD systems and make the Cstate
> > description vendor-agnostic.
> >
> > Signed-off-by: Yazen Ghannam <yazen.ghannam@....com>
> > ---
> >  arch/x86/kernel/acpi/cstate.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kernel/acpi/cstate.c
> > b/arch/x86/kernel/acpi/cstate.c index 8a908ae..4c5dd5d 100644
> > --- a/arch/x86/kernel/acpi/cstate.c
> > +++ b/arch/x86/kernel/acpi/cstate.c
> > @@ -109,7 +109,7 @@ static long
> acpi_processor_ffh_cstate_probe_cpu(void *_cx)
> >  			cx->type);
> >  	}
> >  	snprintf(cx->desc,
> > -			ACPI_CX_DESC_LEN, "ACPI FFH INTEL MWAIT 0x%x",
> > +			ACPI_CX_DESC_LEN, "ACPI FFH X86 MWAIT 0x%x",
> >  			cx->address);
> >  out:
> >  	return retval;
> 
> Are you sure no userspace depends on word "INTEL" there?
> 

So far I've only seen this description printed by cpupower, and it's just for
information.

> Does it make sense to include "X86" there?

I think so, since MWAIT is available on systems from both Intel and AMD.
Also, this FFH implementation can be shared by both vendors.

Though, as I said above, this description seems to be purely informational,
so it's probably not significant either way. I can remove this if preferred.

Thanks,
Yazen