RE: [PATCH] ACPI: Adjust the return value of _REV on x86

[Jason Ekstrand <jason@jlekstrand.net>]

From: Jason Ekstrand <jason@jlekstrand.net>

On Wed, 11 Mar 2015 22:50:47, Matthew Garrett <mjg59@srcf.ucam.org> wrote:
> The ACPI spec describes _REV as:
> 
> "This predefined object evaluates to the revision of the ACPI Specification
>  that the specified \_OS implements"
> 
> We've been assuming that this should increment as ACPICA gains support for
> new versions of the spec. Unfortunately, Windows always reports "2" for this
> value and vendors are now using this as a means to tell whether a system is
> running Windows or Linux. From an HP Envy 15:
> 
> If (LOr (LEqual (_REV, 0x03), LEqual (_REV, 0x05)))
> 
> From a Dell XPS 13:
> 
> If ((_REV == 0x05))

I can confirm that on my 2015 Dell XPS 13, this patch fixes both the audio
and suspend/resume.  I'm running a build of Linus' master branch as of some
time this morning.  Without this patch applied I have no audio and suspend
fails leaving the system unresponsive but the keyboard light still on and
the fan running indefinitely.  With this patch, I get audio and
suspend/resume works normally.

--Jason Ekstrand