On Tue, May 12, 2015 at 10:21:41AM -0700, Matthew Garrett wrote:

Since there's no way to get this working without using new userspace, we're basically stuck with having to support _REV 5. And since we're supposed to support old userspace basically forever, this isn't going to be something that we can just remove in a few months. But since the hardware is intended to be used in I2S mode, we don't want this quirk to be there forever. So we're basically left with adding CONFIG_ACPI_WORKAROUND_BROKEN_DELLS which enables the quirk, default it to Y and then let distributions set it to N when they've got sufficiently new userspace. Unless someone has a better plan?

That makes sense to me given that the firmware doesn't seem to do anything problematic in Linux mode - hopefully we won't have too many more of these systems to contend with.