<html> <head> <base href="https://bugs.freedesktop.org/"> </head> <body> <div> <a class="bz_bug_link bz_status_ASSIGNED " title="ASSIGNED - [GLK] no signal after switch resolution from 1080p@23.98" href="https://bugs.freedesktop.org/show_bug.cgi?id=105887#c69">Comment # 69</a> on <a class="bz_bug_link bz_status_ASSIGNED " title="ASSIGNED - [GLK] no signal after switch resolution from 1080p@23.98" href="https://bugs.freedesktop.org/show_bug.cgi?id=105887">bug 105887</a> from <a class="email" href="mailto:d.scheller.oss@gmail.com" title="Daniel Scheller <d.scheller.oss@gmail.com>"> Daniel Scheller</a> <pre>(In reply to Clinton Taylor from <a href="show_bug.cgi?id=105887#c68">comment #68</a>) > After bashing my head against he wall for several days I have finally > determined that the issue is caused by the HDMI level shifter on the board > and not a driver issue. > > After changing the mode from 1080p24 to 1080p50 the scope shows a valid > clock into the level shifter and a very low amplitude clock on the output to > the connector. Adding a short delay after the Transcoder is disabled appears > to solve the issue with the level shifter. > > I have attached a scope shot of the waveform into the level shifter (yellow > trace) and the output to the connector (blue trace). Thanks for investigating this further and even finding a "proper" driver workaround for this hardware problem. I did a test with msleep(50) at the end of intel_ddi.c:intel_ddi_disable_transcoder_func() (see [1]) on the ASRock board, and this helps the "No signal" issue aswell. I went a bit further and added a modparam to switch between different GLK tests, which by now are "no 12bpc" and "msleep(50)" ([2] is what everything looks like right now, esp. re patches/tests) :-) If anyone else likes to do some testing: I've put installable kernel .debs up at [3] for easy install (Ubuntu Bionic 4.15.0-23.25 proposed, with the patches ontop). To enable any of the workarounds, use the parameter glkhdmi (set to 1 for the 12bit disable hack, set to 2 for the msleep test). Easiest is to add i915.glkhdmi=X (replace X with 1 or 2) to /etc/default/grub into GRUB_CMDLINE_LINUX_DEFAULT, then update-grub, then reboot. Note if you don't set the option or set it to zero, you'll get stock behaviour and the "No signal" issue back. [1] <a href="https://github.com/herrnst/ubuntu-bionic-kernel/commit/f0503e843b8223a2a4572c573a120cd49a8e7134">https://github.com/herrnst/ubuntu-bionic-kernel/commit/f0503e843b8223a2a4572c573a120cd49a8e7134</a> [2] <a href="https://github.com/herrnst/ubuntu-bionic-kernel/compare/Ubuntu-4.15.0-23.25...4.15.0-23.25-glktesting">https://github.com/herrnst/ubuntu-bionic-kernel/compare/Ubuntu-4.15.0-23.25...4.15.0-23.25-glktesting</a> [3] <a href="https://github.com/herrnst/ubuntu-bionic-kernel/tree/4.15.0-23.25-glktesting-deb">https://github.com/herrnst/ubuntu-bionic-kernel/tree/4.15.0-23.25-glktesting-deb</a></pre> </div> <hr> You are receiving this mail because: <ul> <li>You are the QA Contact for the bug.</li> <li>You are on the CC list for the bug.</li> </ul> </body> </html>