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

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Message-ID: <CAErSpo6aBAuK27LwHrdi_X1fxfZ9NN4BkqQj6h4rqHD9ssNnAA@mail.gmail.com>
Date:	Mon, 27 Oct 2014 10:44:09 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Alex Deucher <alexdeucher@...il.com>
Cc:	Shawn Starr <shawn.starr@...ers.com>,
	Alex Deucher <alexander.deucher@....com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	DRI mailing list <dri-devel@...ts.freedesktop.org>,
	Christian König <christian.koenig@....com>
Subject: Re: [Bulk] Re: [3.16-rcX][pciehp][radeon] PCIe HotPlug conflicts with
 radeon GPU

On Sun, Oct 26, 2014 at 11:31 AM, Alex Deucher <alexdeucher@...il.com> wrote:
> On Mon, Oct 13, 2014 at 12:11 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
>> [+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?
>
> Is there a way we could temporarily disable pci hotplug around a GPU reset?

There is pci_ignore_hotplug().  Do you mean something more?  Oh, I
guess you mean a way to disable, then *re*-enable hotplug.  We can
easily add that if that would help.

Bjorn
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