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

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Message-ID: <20131230092043.GB2494@intel.com>
Date:	Mon, 30 Dec 2013 11:20:43 +0200
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PCI <linux-pci@...r.kernel.org>,
	Mike Lothian <mike@...eburn.co.uk>, madcatx@...as.cz,
	Alex Deucher <alexdeucher@...il.com>,
	Dave Airlie <airlied@...ux.ie>, Takashi Iwai <tiwai@...e.de>,
	Joaquín Aramendía <samsagax@...il.com>
Subject: Re: [PATCH][update] ACPIPHP / radeon / nouveau: Fix VGA switcheroo
 problem related to hotplug events

On Sun, Dec 29, 2013 at 10:36:56PM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.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@...eburn.co.uk>
> Reported-and-tested-by: <madcatx@...as.cz>
> Reported-by: Joaquín Aramendía <samsagax@...il.com>
> Cc: Alex Deucher <alexdeucher@...il.com>
> Cc: Dave Airlie <airlied@...ux.ie>
> Cc: Takashi Iwai <tiwai@...e.de>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Cc: 3.12+ <stable@...r.kernel.org> # 3.12+

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