On Sat, Mar 14, 2015 at 12:58 PM, Jason Ekstrand <ja...@jlekstrand.net> wrote: > From: Jason Ekstrand <ja...@jlekstrand.net> > > On Wed, 11 Mar 2015 22:50:47, Matthew Garrett <mj...@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.
A quick update on the Dell XPS 13 for those of you who are following this discussion but aren't aware of the XPS 13-specific discussions. The "problem" triggered by _REV=5 is not a *real* problem. The reason they special-cased it for the XPS 13 is that the sound card is dual-mode and can run over either HDA and I2S. Since the I2S support on Linux isn't great at the moment, they special-cased linux to run it in HDA mode which has good support. The problem is that, in the A01 bios update where they changed this, they made a mistake that left the sound card in an invalid state. A one-line change to the DSDT table in the bios puts it into HDA mode properly and fixes both the audio and suspend/resume issues. They should be coming out with a bios update shortly to fix this. I'm not knowledgeable enough to weigh in on the philosophical issues here, but I thought it was worth explaining the reason for the linux special-casing. In the case of the new XPS 13, Dell was doing something useful with their special-casing, they just made a mistake. If we did start advertising _REV=2 this would cause the laptop (with the fixed bios) to load the sound card in I2S mode and it would be less reliable. --Jason Ekstrand -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/