[Intel-gfx] How does i915 CRT hotplug detection work?

[Bryan Freed]

The only additional information I have is that the irq occurs on a regular
6.47s interval.

Can anyone comment on the mechanism?

bryan.

On Tue, Dec 7, 2010 at 5:08 PM, Bryan Freed <bfreed at chromium.org> wrote:

> I have a pineview system with VGA output that takes anywhere from 1 to 5
> seconds to detect an external monitor plug in/out, and I am trying to reduce
> that latency.  But I do not know how hotplug detection works.
>
> My first sign of detection is in i915_driver_irq_handler() where we
> read PORT_HOTPLUG_STAT (0x61114).  We quickly get
> to i915_hotplug_work_func() and drm_sysfs_hotplug_event() after that, but
> just getting to i915_driver_irq_handler() takes 1 to 5 seconds.
>
> My questions are 1) what takes so long to trigger the irq, and 2) what is
> the irq mechanism?
>
> I first thought the i915 was polling over ddc to detect a monitor status
> change.  But I do not see any activity when I probe DDC_DATA or DDC_CLK.
> I have not probed while plugging in an actual monitor since that removes my
> easy-to-probe point.
>
> Does i915 look for a glitch on one of the signals before it probes DDC?
>
> bryan.
>
>
>
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