i915 monitor hotplug on 4.1/4.4 PREEMPT

i915 monitor hotplug on 4.1/4.4 PREEMPT

[Nicolae Rosia]

Hello,

Monitor hotplugging seems to be broken on latest 4.1/4.4 RT kernel with i915.
I have tested this on non-RT kernel and it works.
I get an udev event for unplugging, but there's no event generated for
plugging the monitor back in.

Any pointers are appreciated.

Best regards,
Nicolae

Re: i915 monitor hotplug on 4.1/4.4 PREEMPT

[Jani Nikula]

On Thu, 20 Oct 2016, Nicolae Rosia <nicolae.rosia.oss@gmail.com> wrote:
> Monitor hotplugging seems to be broken on latest 4.1/4.4 RT kernel with i915.
> I have tested this on non-RT kernel and it works.
> I get an udev event for unplugging, but there's no event generated for
> plugging the monitor back in.

Does it work on non-RT? Does it work on v4.8 or v4.9-rc1?

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Technology Center

Re: i915 monitor hotplug on 4.1/4.4 PREEMPT

[David Weinehall]

On Thu, Oct 20, 2016 at 03:28:10PM +0300, Jani Nikula wrote:
> On Thu, 20 Oct 2016, Nicolae Rosia <nicolae.rosia.oss@gmail.com> wrote:
> > Monitor hotplugging seems to be broken on latest 4.1/4.4 RT kernel with i915.
> > I have tested this on non-RT kernel and it works.

The answer to your first question seems to be here :)

> > I get an udev event for unplugging, but there's no event generated for
> > plugging the monitor back in.
> 
> Does it work on non-RT? Does it work on v4.8 or v4.9-rc1?

The second one is relevant though. 4.1 is pre-historic, 4.4 is ancient.


Kind regards, David
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Re: [Intel-gfx] i915 monitor hotplug on 4.1/4.4 PREEMPT

[Jani Nikula]

On Thu, 20 Oct 2016, David Weinehall <tao@kernel.org> wrote:
> On Thu, Oct 20, 2016 at 03:28:10PM +0300, Jani Nikula wrote:
>> On Thu, 20 Oct 2016, Nicolae Rosia <nicolae.rosia.oss@gmail.com> wrote:
>> > Monitor hotplugging seems to be broken on latest 4.1/4.4 RT kernel with i915.
>> > I have tested this on non-RT kernel and it works.
>
> The answer to your first question seems to be here :)

*blush*

>> > I get an udev event for unplugging, but there's no event generated for
>> > plugging the monitor back in.
>> 
>> Does it work on non-RT? Does it work on v4.8 or v4.9-rc1?
>
> The second one is relevant though. 4.1 is pre-historic, 4.4 is ancient.

I think the honest answer here is that we do not have the resources to
debug RT vs. non-RT issues all that much in general, and especially not
for such old kernels. RT is not in our focus, and hotplug has proved to
be hard enough on non-RT. Nothing to be proud of, but we have 500+ bugs
open over at the freedesktop.org bugzilla, most for relatively recent
non-RT kernels.

Even if we fixed this upstream (and it would have to be fixed upstream
to be backported) it's a huge problem that the feedback loop for RT
kernels has such a long delay. If we break something for RT, it takes
forever for us to find out.


BR,
Jani.

-- 
Jani Nikula, Intel Open Source Technology Center

Re: [Intel-gfx] i915 monitor hotplug on 4.1/4.4 PREEMPT

[Nicolae Rosia]

Hi,

On Thu, Oct 20, 2016 at 3:57 PM, David Weinehall <tao@kernel.org> wrote:
>> > I get an udev event for unplugging, but there's no event generated for
>> > plugging the monitor back in.
>>
>> Does it work on non-RT? Does it work on v4.8 or v4.9-rc1?
>
> The second one is relevant though. 4.1 is pre-historic, 4.4 is ancient.
I just tested this on v4.8.2-rt2 and it works.

Any tips on what I should do next, excluding the upgrade :-) ?

Best regards,
Nicolae
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Re: [Intel-gfx] i915 monitor hotplug on 4.1/4.4 PREEMPT

[Daniel Vetter]

On Thu, Oct 20, 2016 at 05:09:52PM +0300, Nicolae Rosia wrote:
> Hi,
> 
> On Thu, Oct 20, 2016 at 3:57 PM, David Weinehall <tao@kernel.org> wrote:
> >> > I get an udev event for unplugging, but there's no event generated for
> >> > plugging the monitor back in.
> >>
> >> Does it work on non-RT? Does it work on v4.8 or v4.9-rc1?
> >
> > The second one is relevant though. 4.1 is pre-historic, 4.4 is ancient.
> I just tested this on v4.8.2-rt2 and it works.
> 
> Any tips on what I should do next, excluding the upgrade :-) ?

Very, very likely the answer is "upgrade", because:

$ git log --oneline v4.4..v4.8 -- drivers/gpu/drm/i915/ | wc -l
1931

That's not even counting the drm core changes, which also might be
relevant. Normally a revert bisect (to figure out the bugfix, hoping that
it's just 1 patch and not an entire series) would be an option. But since
-rt is still an add-on you'd need to rebase the entire -rt patchset every
time. That's impossible.

If you have way too much time, and know what you're doing another option
might be to backport all of drm (to avoid conflicts between drm core and
i915) from 4.8 to 4.4. No guarantee at all it'll work, and we generally
keep a few people busy for a while every time we have to do that
internally for some product team.

So yeah, "upgrade" is very likely is.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [Intel-gfx] i915 monitor hotplug on 4.1/4.4 PREEMPT

[Nicolae Rosia]

Hello,

On Fri, Oct 21, 2016 at 3:27 PM, Daniel Vetter <daniel@ffwll.ch> wrote:
> So yeah, "upgrade" is very likely is.
I see...

i915.disable_power_well=0 seems to do the trick.
Is it safe to use? The kernel gets tainted because of this.

Regards,
Nicolae

Re: [Intel-gfx] i915 monitor hotplug on 4.1/4.4 PREEMPT

[Daniel Vetter]

On Fri, Oct 21, 2016 at 04:21:53PM +0300, Nicolae Rosia wrote:
> Hello,
> 
> On Fri, Oct 21, 2016 at 3:27 PM, Daniel Vetter <daniel@ffwll.ch> wrote:
> > So yeah, "upgrade" is very likely is.
> I see...
> 
> i915.disable_power_well=0 seems to do the trick.
> Is it safe to use? The kernel gets tainted because of this.

We taint the kernel on principle if you touch any of these debug options,
i.e. don't send us bug reports if it blows up. Because it'll be running
untested codepaths.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch