On Tue, Jan 6, 2015 at 10:21 PM, Robert Morell <rmorell@xxxxxxxxxx> wrote:
>
> FWIW, I've seen that exact symptom on some monitors when the +5V pin on
> the DVI or HDMI cable from the GPU isn't enabled (or isn't providing
> enough current). Some monitors power the i2c/edid/DDC logic from that
> +5V either exclusively or when in the DPMS off state, and the i2c chip
> will just stop responding after a few cycles if not provided sufficient
> power.
That makes a ton of sense, especially the "when in DPMS off state" case.
I'll do the drm.debug=0xe thing, and maybe Daniel can make more sense
of the details. Maybe the i2c driver ends up powering down too soon
(or maybe it needs to power up a bit earlier)?
This is a bog-standard intel motherboard (DH87RL), but I actually
needed to update the BIOS for it to get it to POST reliably with this
monitor. I was blaming that on the odd 3840x2160@30Hz mode, but maybe
it's related to the EDID being finicky wrt i2c power.
I'm assuming even the hdmi +5V line is under sw control at least for
power management reasons. Maybe dpms off turns it off, and shouldn't?
My monitor actually says "No HDMI (HML) Cable" when I do "xset dpms
force off". Maybe that's normal, but maybe that's indicative of dpms
turning things a bit *too* off?
Linus
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