From: <Mario.Limonciello@dell.com>
To: <kernel@kempniu.pl>, <dvhart@infradead.org>
Cc: <rjw@rjwysocki.net>, <len.brown@intel.com>,
<pali.rohar@gmail.com>, <corentin.chary@gmail.com>,
<luto@kernel.org>, <andriy.shevchenko@linux.intel.com>,
<linux-kernel@vger.kernel.org>,
<platform-driver-x86@vger.kernel.org>, <linux-pm@vger.kernel.org>
Subject: RE: RFC: WMI Enhancements
Date: Thu, 13 Apr 2017 13:29:41 +0000 [thread overview]
Message-ID: <3370431810bd4bc09fd9eb16eb9abea5@ausx13mpc120.AMER.DELL.COM> (raw)
In-Reply-To: <20170413073228.GB1462@ozzy.nask.waw.pl>
> -----Original Message-----
> From: Michał Kępień [mailto:kernel@kempniu.pl]
> Sent: Thursday, April 13, 2017 2:32 AM
> To: Darren Hart <dvhart@infradead.org>
> Cc: Rafael Wysocki <rjw@rjwysocki.net>; Len Brown <len.brown@intel.com>;
> Pali Rohár <pali.rohar@gmail.com>; Corentin Chary
> <corentin.chary@gmail.com>; Limonciello, Mario
> <Mario_Limonciello@Dell.com>; Andy Lutomirski <luto@kernel.org>; Andy
> Shevchenko <andriy.shevchenko@linux.intel.com>; LKML <linux-
> kernel@vger.kernel.org>; platform-driver-x86@vger.kernel.org; linux-
> pm@vger.kernel.org
> Subject: Re: RFC: WMI Enhancements
>
> > Hi All,
> >
> > There are a few parallel efforts involving the Windows Management
> > Instrumentation (WMI)[1] and dependent/related drivers. I'd like to
> > have a round of discussion among those of you that have been involved
> > in this space before we decide on a direction.
> >
> > The WMI support in the kernel today fairly narrowly supports a handful
> > of systems. Andy L. has a work-in-progress series [2] which converts
> > wmi into a platform device and a proper bus, providing devices for
> > dependent drivers to bind to, and a mechanism for sibling devices to
> communicate with each other.
> > I've reviewed the series and feel like the approach is sound, I plan
> > to carry this series forward and merge it (with Andy L's permission).
> >
> > Are there any objections to this?
>
> Back in January 2016, I sent Andy a few minor comments about this series. A
> year later, I offered to iron out the remaining issues and resubmit the series in
> Andy's name when I find the time. Sadly, things have changed a bit for me
> since that time and it is unlikely that I will be able to deliver, for which I am
> sorry.
>
> However, browsing Andy's branch I see that most issues have been resolved,
> though I think some of my remarks [1] have either been missed or silently
> refuted :)
>
> Anyway, I also like this approach and I think this series is a valuable cleanup.
>
> > In Windows, applications interact with WMI more or less directly. We
> > don't do this in Linux currently, although it has been discussed in
> > the past [3]. Some vendors will work around this by performing
> > SMI/SMM, which is inefficient at best. Exposing WMI methods to
> > userspace would bring parity to WMI for Linux and Windows.
> >
> > There are two principal concerns I'd appreciate your thoughts on:
> >
> > a) As an undiscoverable interface (you need to know the method
> > signatures ahead of time), universally exposing every WMI "device" to
> > userspace seems like "a bad idea" from a security and stability
> > perspective. While access would certainly be privileged, it seems more
> > prudent to make this exposure opt-in. We also handle some of this with
> > kernel drivers and exposing those "devices" to userspace would enable
> > userspace and the kernel to fight over control. So - if we expose WMI
> > devices to userspace, I believe this should be done on a case by case
> > basis, opting in, and not by default as part of the WMI driver
> > (although it can provide the mechanism for a sub-driver to use), and possibly
> a devmode to do so by default.
> >
> > b) The mechanism to expose WMI devices to userspace must allow for
> > atomic operation, which would exclude a sysfs interface involving multiple
> files.
> > Something like an ioctl or a char dev would be more appropriate.
> >
> > Does anyone think differently regarding a) or b) ?
>
> 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.
> 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.
>
> I am biased here as I have had my own struggles with WMI in the past, but it
> looks like a layer of indirection which brings little value, yet is tricky to expose
> properly. If there is a real-life use case that makes this idea worthwhile, I
> would love to be enlightened.
>
> > Secondarily, Andy L created a simple driver to expose the MOF buffer
> > [2] to userspace which could be consumed by a userspace tool to create
> > sources for an interface to the exposed WMI methods.
>
> +1 for the idea, it makes figuring out what the firmware actually
> exposes through WMI a bit easier. After skimming through the driver's code, I
> would only recommend to review the included headers (linux/input/sparse-
> keymap.h, linux/dmi.h and acpi/video.h all seem redundant to me).
>
> What we still need, though, is an open source version of wmiofck.exe. I am
> unaware of anything like that existing and installing the Windows Driver Kit
> just to run one command which spits out a single *.h file is not something I
> would describe as convenient (been there).
>
> [1] https://www.spinics.net/lists/platform-driver-x86/msg08201.html
>
> --
> Best regards,
> Michał Kępień
next prev parent reply other threads:[~2017-04-13 13:42 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-12 23:08 RFC: WMI Enhancements Darren Hart
2017-04-13 7:32 ` Michał Kępień
2017-04-13 13:29 ` Mario.Limonciello [this message]
2017-04-13 13:51 ` Pali Rohár
2017-04-13 15:34 ` Andy Lutomirski
2017-04-13 15:40 ` Mario.Limonciello
2017-04-13 16:06 ` Darren Hart
2017-04-13 15:40 ` Mario.Limonciello
2017-04-18 7:36 ` Andy Shevchenko
2017-04-18 14:08 ` Mario.Limonciello
2017-04-13 15:32 ` Andy Lutomirski
2017-04-13 15:39 ` Pali Rohár
2017-04-13 15:44 ` Andy Lutomirski
2017-04-13 16:09 ` Darren Hart
2017-04-13 15:55 ` Mario.Limonciello
2017-04-13 15:57 ` Andy Lutomirski
2017-04-13 16:54 ` Mario.Limonciello
2017-04-13 17:06 ` Darren Hart
2017-04-13 17:39 ` Mario.Limonciello
2017-04-13 17:44 ` Andy Lutomirski
2017-04-13 17:49 ` Mario.Limonciello
2017-04-18 7:54 ` Pali Rohár
2017-04-18 16:56 ` Darren Hart
2017-04-18 19:28 ` Pali Rohár
2017-04-13 17:02 ` Darren Hart
2017-04-13 17:32 ` Andy Lutomirski
2017-04-13 17:45 ` Mario.Limonciello
2017-04-13 16:08 ` Darren Hart
2017-04-13 7:33 ` Pali Rohár
2017-04-13 16:56 ` Darren Hart
2017-04-13 20:38 ` Mario.Limonciello
2017-04-13 23:51 ` Darren Hart
2017-04-14 17:42 ` Mario.Limonciello
2017-04-14 18:27 ` Darren Hart
2017-04-14 19:04 ` Mario.Limonciello
2017-04-14 22:45 ` Rafael J. Wysocki
2017-04-14 23:05 ` Darren Hart
2017-04-17 22:03 ` Andy Lutomirski
2017-04-17 23:10 ` Darren Hart
2017-04-18 13:07 ` Rafael J. Wysocki
2017-04-18 16:33 ` Darren Hart
2017-04-18 19:28 ` Pali Rohár
2017-04-18 22:49 ` Darren Hart
2017-04-19 7:52 ` Pali Rohár
2017-04-19 16:29 ` Mario.Limonciello
2017-04-19 16:54 ` Pali Rohár
2017-04-19 17:24 ` Mario.Limonciello
2017-04-20 13:14 ` Pali Rohár
2017-04-20 20:44 ` Darren Hart
2017-05-05 21:55 ` Mario.Limonciello
2017-05-05 23:44 ` Darren Hart
2017-05-06 0:51 ` Mario.Limonciello
2017-05-06 1:25 ` Andy Lutomirski
2017-05-08 15:29 ` Darren Hart
2017-05-08 15:36 ` Mario.Limonciello
2017-05-08 15:47 ` Darren Hart
2017-05-08 16:00 ` Mario.Limonciello
2017-05-08 16:04 ` Andy Shevchenko
[not found] ` <CAOg5c--wkQgvsmhTynAKyG9iWaHjRWC5Z+MXzVJVw66vxSz4Zw@mail.gmail.com>
2017-05-08 18:26 ` Mario.Limonciello
2017-05-08 19:09 ` Darren Hart
2017-05-08 19:11 ` Mario.Limonciello
2017-05-08 17:17 ` Pali Rohár
2017-05-08 19:21 ` Mario.Limonciello
2017-05-08 20:59 ` Pali Rohár
2017-05-08 21:18 ` Mario.Limonciello
2017-05-08 22:17 ` Pali Rohár
2017-05-09 1:10 ` Mario.Limonciello
2017-05-09 7:29 ` Pali Rohár
2017-05-09 18:10 ` Mario.Limonciello
2017-05-09 19:04 ` Andy Shevchenko
2017-05-09 19:16 ` Mario.Limonciello
2017-05-09 19:26 ` Andy Shevchenko
2017-05-09 22:38 ` Pali Rohár
2017-05-09 19:19 ` Pali Rohár
2017-04-20 14:17 ` Christoph Hellwig
2017-04-18 21:14 ` Rafael J. Wysocki
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