linux-kernel - Re: [Bulk] Re: [3.16-rcX][pciehp][radeon] PCIe HotPlug conflicts with radeon GPU

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Date:	Mon, 13 Oct 2014 10:11:28 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Shawn Starr <shawn.starr@...ers.com>
Cc:	Kernel development list <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Alex Deucher <alexander.deucher@....com>,
	Christian König <christian.koenig@....com>,
	DRI mailing list <dri-devel@...ts.freedesktop.org>
Subject: Re: [Bulk] Re: [3.16-rcX][pciehp][radeon] PCIe HotPlug conflicts with
 radeon GPU

[+cc Alex, Christian, dri-devel]

On Sat, Oct 11, 2014 at 1:37 PM, Shawn Starr <shawn.starr@...ers.com> wrote:
> On September 11, 2014 04:26:21 PM Bjorn Helgaas wrote:
>> [+cc linux-pci]
>>
>> On Sat, Aug 2, 2014 at 10:02 AM, Shawn Starr <shawn.starr@...ers.com> wrote:
>> > Hello devs,
>> >
>> > There are two issues I am encountering with the PCIe Hotplug driver on my
>> > Lenovo Laptop (W500). I note this goes back further than 3.15.
>> >
>> > It is noted here:
>> > http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=
>> > f244d8b623dae7a7bc695b0336f67729b95a9736
>> > https://bugzilla.kernel.org/show_bug.cgi?id=79701
>> >
>> > And my open bug here:
>> > https://bugzilla.kernel.org/show_bug.cgi?id=77261
>> >
>> > 1) If I enable the device to use both the integrated and discrete GPU,
>> > pciehp will decide to force unload radeon because it puts itself into a
>> > power saving state, fails back to the Intel integrated GPU in this case
>> > unless I tell radeon.ko to runpm=0 (no power management, then pciehp wont
>> > touch it).
>> >
>> > 2) If the Radeon GPU resets and you use pci_reset=1 for kernel module
>> > option, pciehp decides to force unload radeon even though the GPU is
>> > trying to setup after failing.
>> >
>> > Kernel I am using right now: 3.16.0-0.rc7.git3.1.fc21.x86_64 (about to
>> > boot into snapshot kernel-core-3.16.0-0.rc7.git4.1.fc21.x86_64)
>> Hi Shawn,
>>
>> Thanks for the report and sorry that it got dropped.  But I see you're
>> cc'd on https://bugzilla.kernel.org/show_bug.cgi?id=79701, so you've
>> probably seen the work there.  If you can try out the patches I just
>> posted, that would be great.
>>
>> Bjorn
>
> Hi Bjorn,
>
> For #1) This is fixed in linux-next (tracking 3.18.0-0.rc0.git1.2.fc22.1.x86_64
> nondebug kernel for Fedora). PCIe HotPlug no longer unloads radeon. For this
> bugzilla report we can close it.
>
> #2) This still has weird results however, radeon.hard_reset=1 is experimental
> and while it attempts to reset GPU, PCIe HotPlug seems to interact in this.
>
> This can be tested by adding to grub command line radeon.hard_reset=1.
> When X has started up, trigger a reset by cat
> /sys/kernel/debug/dri/#/radeon_gpu_reset. It will output 0, cat it again will
> show 1.
>
> Attempt to drag a window. The this will trigger a GPU reset, but fail to
> recover, its unknown if PCIe HotPlug is preventing a proper reset or not but
> there is pciehp calls in the stack trace.

A PCIe device reset usually looks like a hotplug event because the
PCIe link goes down and comes back up.  As far as the PCI core is
concerned, it can't tell the difference between (1) a simple reset
where the link bounces and (2) removal of one device followed by
addition of another.

b440bde74f04 ("PCI: Add pci_ignore_hotplug() to ignore hotplug events
for a device") addressed this for some similar cases, but it looks
like we probably need some more calls to pci_ignore_hotplug() in the
radeon driver reset methods.

Can you please open a bugzilla and attach the complete dmesg log,
including the GPU reset and recovery failure?

Bjorn
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