On Wed, Jan 7, 2015 at 6:07 PM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > 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? Not sure whether that'd be the same voltage rails, but i915.disable_power_wells=0 disable all the runtime pm we do (which does kick in for dpms off and shut down the entire display block and a bunch more). Maybe we just need to detect that the chip dropped off the bus and retry after 50ms (to give the caps some time to charge). -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
