Re: [PATCH][update] ACPIPHP / radeon / nouveau: Fix VGA switcheroo problem related to hotplug events

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Sun, Dec 29, 2013 at 10:36:56PM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> The changes in the ACPI-based PCI hotplug (ACPIPHP) subsystem made
> during the 3.12 development cycle uncovered a problem with VGA
> switcheroo that on some systems, when the device-specific method
> (ATPX in the radeon case, _DSM in the nouveau case) is used to turn
> off the discrete graphics, the BIOS generates ACPI hotplug events for
> that device and those events cause ACPIPHP to attempt to remove the
> device from the system (they are events for a device that was present
> previously and is not present any more, so that's what should be done
> according to the spec).  Then, the system stops functioning correctly.
> 
> Since the hotplug events in question were simply silently ignored
> previously, the least intrusive way to address that problem is to
> make ACPIPHP ignore them again.  For this purpose, introduce a new
> ACPI device flag, no_hotplug, and modify ACPIPHP to ignore hotplug
> events for PCI devices whose ACPI companions have that flag set.
> Next, make the radeon and nouveau switcheroo detection code set the
> no_hotplug flag for the discrete graphics' ACPI companion.
> 
> Fixes: bbd34fcdd1b2 (ACPI / hotplug / PCI: Register all devices under the given bridge)
> References: https://bugzilla.kernel.org/show_bug.cgi?id=61891
> References: https://bugzilla.kernel.org/show_bug.cgi?id=64891
> Reported-and-tested-by: Mike Lothian <mike@fireburn.co.uk>
> Reported-and-tested-by: <madcatx@atlas.cz>
> Reported-by: Joaquín Aramendía <samsagax@gmail.com>
> Cc: Alex Deucher <alexdeucher@gmail.com>
> Cc: Dave Airlie <airlied@linux.ie>
> Cc: Takashi Iwai <tiwai@suse.de>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Cc: 3.12+ <stable@vger.kernel.org> # 3.12+

FWIW, Thunderbolt hotplug still works fine after this patch is applied :)