From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Subject: Re: [PATCH 5/5] ACPI: Tie ACPI backlight devices to PCI devices if possible Date: Sun, 6 Feb 2011 21:35:07 +0100 Message-ID: <201102062135.08171.rjw@sisk.pl> References: <1295033065-13450-1-git-send-email-mjg@redhat.com> <1295033065-13450-5-git-send-email-mjg@redhat.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-2" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1295033065-13450-5-git-send-email-mjg@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: Matthew Garrett Cc: akpm@linux-foundation.org, intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, rpurdie@rpsys.net List-Id: dri-devel@lists.freedesktop.org On Friday, January 14, 2011, Matthew Garrett wrote: > Dual-GPU machines may provide more than one ACPI backlight interface. Tie > the backlight device to the GPU in order to allow userspace to identify > the correct interface. > > Signed-off-by: Matthew Garrett Sorry for the late response, but I've just realized there's a problem with this patch. > --- > drivers/acpi/video.c | 15 ++++++++++++++- > 1 files changed, 14 insertions(+), 1 deletions(-) > > diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c > index a9eec8c..a18e497 100644 > --- a/drivers/acpi/video.c > +++ b/drivers/acpi/video.c > @@ -782,6 +782,9 @@ static void acpi_video_device_find_cap(struct acpi_video_device *device) > > if (acpi_video_backlight_support()) { > struct backlight_properties props; > + struct pci_dev *pdev; > + acpi_handle acpi_parent; > + struct device *parent = NULL; > int result; > static int count = 0; > char *name; > @@ -794,10 +797,20 @@ static void acpi_video_device_find_cap(struct acpi_video_device *device) > return; > count++; > > + acpi_get_parent(device->dev->handle, &acpi_parent); > + > + pdev = acpi_get_pci_dev(acpi_parent); > + if (pdev) { > + parent = &pdev->dev; > + pci_dev_put(pdev); > + } I'm afraid you can't do that or suspend problems will happen. Namely, the PM core assumes that parents will be registered before their children and it is a very strong assumption. If violated, it may lead to a suspend sequence deadlock. Unfortunately, it looks like the ACPI video device is registered before the PCI device that's becoming it's parent, so the above assumption will be violated. Thanks, Rafael