"EDID checksum is invalid"

[Robert Morell]

On Tue, Jan 06, 2015 at 10:07:58PM -0800, Keith Packard wrote:
> * PGP Signed by an unknown key
> 
> Linus Torvalds <torvalds at linux-foundation.org> writes:
> 
> > it looks like the beginning is the same, but then it just turns to all
> > ones at a random point (even *within* a byte).
> 
> Looks like the EDID ROM is dropping off the i2c bus in the middle of the
> transfer. Wonder if it's being 'clever' if things go too slowly at some
> point, or if there's a bug in the DDC code that's in use.

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.

- Robert