[Intel-gfx] i915 SNB: hotplug events when charging causing poor interactivity

Daniel Vetter daniel at ffwll.ch
Tue Feb 21 21:02:54 CET 2012

On Tue, Feb 21, 2012 at 01:37:37PM +0000, Daniel J Blueman wrote:
> On 16 February 2012 13:07, Daniel Vetter <daniel at ffwll.ch> wrote:
> > On Thu, Feb 16, 2012 at 11:44:46AM +0000, Daniel J Blueman wrote:
> >> When charging Dell E5420 laptops, I see the Sandy Bridge South Display
> >> Engine port C hotplug interrupt fire consistently at around 20Hz. Each
> []
> >> Notably, when only using battery or only using AC, the port C
> >> interrupts don't fire. It feels like the platform is using South
> >> Display Port C for GPIO/I2C; setting the port C pulse duration from
> >> 2ms to 100ms doesn't change the behaviour. I'll dump off the GPIO
> >> settings, but what else is good to debug this?
> >
> > Yep, dumping the register state (intel_reg_dumper from intel-gpu-tools is
> > handy for that) in the different situations sounds useful.
> []
> > If this is indeed the bios we need to quirk this away. But I think we
> > should check first whether we don't butcher something else accidently.
> When charging the battery, I see the SDE_PORTB_HOTPLUG, PORTC, PORTD
> and SDE_AUX_MASK bits set (sometimes at different times) at ~20Hz
> until the battery is charged, which is disconcerting.
> Hotplugging a HDMI cable, SDE_PORTB_HOTPLUG and SDE_AUX_MASK bits are
> set once, so we can't mask these on this platform.
> Attached are the reg dumps. We see the backlight register
> (BLC_PWM_CPU_CTL) and the A surface register (DSPASURF) vary across
> multiple reads as expected.
> Any ideas?

Nope, as in absolutely no idea. The only idea I have is that the expects
us to do something with either acpi or opregion that we currently don't,
but that's just handwaving.

So I think you're left with filing a bug report with all the things you've
gathered and hoping that we stumble over the missing piece of
documentation :(
Daniel Vetter
Mail: daniel at ffwll.ch
Mobile: +41 (0)79 365 57 48

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