[Intel-gfx] Does the i915 driver (and hardware) properly handle DPMS on/off?

[Bryan Freed]

I will accept a redirect to another list if this is the wrong one.

When I run a loop of "xset dpms force off; sleep 1; xset dpms force on;
sleep 1" to repeatedly turn on and off the panel (connected through i915
LVDS), it does not come back on after a while.  The backlight comes on, but
the framebuffer is not displayed.

I probed the LVD_A_CLKM signal and saw that the "force on" would transition
it from 0V to 1V, but I would not see the clock oscillation that I usually
see.
I do not have a differential probe to see the pretty picture with both CLKM
and CLKP, but I expect to see _something_.  And this corresponds with my
blank screen.

Has this been reported before?

I dumped a bunch of i915 registers, but I do not see a significant
difference between "working" and "not working".  Just some (undocumented, as
far as I can tell) sequential counter at 0x61100 and a scanline counter at
0x71000.

bryan.
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