linux-kernel - RE: RFC: WMI Enhancements

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Date:   Thu, 13 Apr 2017 15:40:41 +0000
From:   <Mario.Limonciello@...l.com>
To:     <pali.rohar@...il.com>, <hdegoede@...hat.com>
CC:     <kernel@...pniu.pl>, <dvhart@...radead.org>, <rjw@...ysocki.net>,
        <len.brown@...el.com>, <corentin.chary@...il.com>,
        <luto@...nel.org>, <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: Pali Rohár [mailto:pali.rohar@...il.com]
> Sent: Thursday, April 13, 2017 8:51 AM
> To: Limonciello, Mario <Mario_Limonciello@...l.com>; Hans de Goede
> <hdegoede@...hat.com>
> Cc: kernel@...pniu.pl; dvhart@...radead.org; rjw@...ysocki.net;
> len.brown@...el.com; corentin.chary@...il.com; luto@...nel.org;
> 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 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.
> 	

A normal user shouldn't be using it directly, but libsmbios is used by a few open 
source tools as a dependency.  It's also used in many Dell manageability tools.

> 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?
> 
> --
> Pali Rohár
> pali.rohar@...il.com