Comment 1 for bug 1374607

This week I tried HDMI again on my system, and noticed it was completely broken.
Got just no signal on my screen.

I knew it was working some months (and upgrades) ago.
After testing I found out the issue was introduced between kernel v3.14 and v3.15.

Situation:
Insert HDMI cable into my laptop, and no signal on the external display.

The dmesg fills with errors also:
[ 186.210622] nouveau E[ PDISP][0000:01:00.0] INVALID_STATE [UNK08] chid 0 mthd 0x0080 data 0x00000000
[ 186.210627] nouveau E[ PDISP][0000:01:00.0] Core:
[ 186.210634] nouveau E[ PDISP][0000:01:00.0] 0x0084: 0x5dc34da1 -> 0x80000000
[ 186.210640] nouveau E[ PDISP][0000:01:00.0] 0x0088: 0x00000000

etc.

After some git bisect playtime, I found out the following commit caused the issue:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/gpu/drm/nouveau?id=05c63c2ff23a80b654d6c088ac3ba21628db0173

So I went back to stable 3.16 (Ubuntu Utopic version), and did a git revert for that commit.
And yep, HDMI output was working again, and no more nouveau errors in dmesg.

My device:
[ 30.823267] nouveau [ DEVICE][0000:01:00.0] BOOT0 : 0x0c1a00a1
[ 30.823269] nouveau [ DEVICE][0000:01:00.0] Chipset: GF108 (NVC1)
[ 30.823270] nouveau [ DEVICE][0000:01:00.0] Family : NVC0

Laptop dell xps 15 l502x