linux-kernel - Re: RFC: WMI Enhancements

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Message-ID: <20170413160606.GA2064@fury>
Date:   Thu, 13 Apr 2017 09:06:06 -0700
From:   Darren Hart <dvhart@...radead.org>
To:     Mario.Limonciello@...l.com
Cc:     luto@...nel.org, pali.rohar@...il.com, hdegoede@...hat.com,
        kernel@...pniu.pl, 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

On Thu, Apr 13, 2017 at 03:40:08PM +0000, Mario.Limonciello@...l.com wrote:
> > -----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.

Agreed on this point as well.

-- 
Darren Hart
VMware Open Source Technology Center