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

[Alex Deucher]

On Mon, Oct 27, 2014 at 12:44 PM, Bjorn Helgaas <bhelgaas at google.com> wrote:
> On Sun, Oct 26, 2014 at 11:31 AM, Alex Deucher <alexdeucher at gmail.com> wrote:
>> On Mon, Oct 13, 2014 at 12:11 PM, Bjorn Helgaas <bhelgaas at google.com> wrote:
>>> [+cc Alex, Christian, dri-devel]
>>>
>>> On Sat, Oct 11, 2014 at 1:37 PM, Shawn Starr <shawn.starr at rogers.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 at rogers.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.

Exactly.  I was thinking I could disable hotplug, do the gpu hard
reset, then re-enable hotplug.

Alex