linux-kernel - RE: RFC: WMI Enhancements

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Date:   Thu, 13 Apr 2017 15:40:08 +0000
From:   <Mario.Limonciello@...l.com>
To:     <luto@...nel.org>, <pali.rohar@...il.com>
CC:     <hdegoede@...hat.com>, <kernel@...pniu.pl>, <dvhart@...radead.org>,
        <rjw@...ysocki.net>, <len.brown@...el.com>,
        <corentin.chary@...il.com>, <andriy.shevchenko@...ux.intel.com>,
        <linux-kernel@...r.kernel.org>,
        <platform-driver-x86@...r.kernel.org>, <linux-pm@...r.kernel.org>
Subject: RE: RFC: WMI Enhancements

> -----Original Message-----
> From: Andy Lutomirski [mailto:luto@...nel.org]
> Sent: Thursday, April 13, 2017 10:35 AM
> To: Pali Rohár <pali.rohar@...il.com>
> Cc: Limonciello, Mario <Mario_Limonciello@...l.com>; Hans de Goede
> <hdegoede@...hat.com>; Michał Kępień <kernel@...pniu.pl>; Darren Hart
> <dvhart@...radead.org>; Rafael J. Wysocki <rjw@...ysocki.net>; Len Brown
> <len.brown@...el.com>; corentin.chary@...il.com; Andrew Lutomirski
> <luto@...nel.org>; Andy Shevchenko <andriy.shevchenko@...ux.intel.com>;
> linux-kernel@...r.kernel.org; platform-driver-x86@...r.kernel.org; linux-
> pm@...r.kernel.org
> Subject: Re: RFC: WMI Enhancements
> 
> On Thu, Apr 13, 2017 at 6:51 AM, Pali Rohár <pali.rohar@...il.com> wrote:
> > On Thursday 13 April 2017 13:29:41 Mario.Limonciello@...l.com wrote:
> >> > Please pardon my ignorance, but what do we actually gain by
> >> > exposing WMI to userspace?  Enabling applications to fetch SMBIOS
> >> > data?  We already have an interface for that.  Enabling applications to
> receive input events?  Likewise.
> >>
> >> Input notifications are just one aspect that received over WMI.  I
> >> don't see any reason to move the notifications out of the kernel.
> >>
> >> In terms of userspace applications, once a WMI interface to userspace
> >> is available libsmbios would change over to that.  Applications using
> libsmbios would benefit.
> >
> > Really libsmbios matters here? Hans (added to thread) wrote that
> > libsmbios is a relic, something of ages long gone by and a normal user
> > should never use it.
> >
> > If this is truth and libsmbios should not be used, then we probably do
> > not need to care about it in changes for WMI.
> >
> > Hans, Mario, any comment/clarification about it?
> >
> >> > You mentioned WMI's efficiency compared to SMI/SMM, but is it a
> >> > difference significant enough for anyone to notice?
> >>
> >> At least for Dell there are optimizations being made when data is
> >> requested over the WMI-ACPI wrapper instead of directly via SMI/SMM.
> >>
> >> For example if the data is a "static" table or the request is to
> >> something that is passed thru to the EC it's a big waste of effort to put the
> CPU in SMM.
> >>
> >> The savings there is significant.
> >
> > Maybe we can use this Dell WMI-ACPI wrapper for kernel drivers instead
> > of current SMI/SMM direct access?
> >
> 
> This would make sense to me.  IIRC the only functional difference is the way
> that pointers are handled.  It shouldn't be that hard to make it work for both
> variants, though.  It could look like:
> 
> buf = dell_smbios_alloc(...);
> dell_smbios_put_pointer(buf, offset of pointer, offset of pointee);
> dell_smbios_call(buf);
> 
> or similar.

Yes, I was going to encourage that kernel change after this WMI discussion 
had some conclusions.