<div dir="ltr">Hello all,<div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><br></div><div>TL;DR: my questions concern the following two topics:<br></div><div>- CRTCs and Intel integrated GPUs</div><div>- intel-virtual-output utility<br></div><div><br></div><div>I have a laptop with both an Intel integrated GPU and an AMD discrete GPU.</div><div><br></div><div>```</div><div>➜ ~ xrandr --listproviders<br>Providers: number : 2<br>Provider 0: id: 0x70 cap: 0x9, Source Output, Sink Offload crtcs: 4 outputs: 8 associated providers: 1 name:Intel<br>Provider
1: id: 0x44 cap: 0x6, Sink Output, Source Offload crtcs: 5 outputs: 0
associated providers: 1 name:AMD Radeon Pro WX3100 @ pci:0000:3b:00.0<br></div><div>```</div><div><br></div><div>I am certain that both are configured correctly:</div><div><br></div><div>```</div><div>➜ ~ DRI_PRIME=0 glxinfo | grep "OpenGL renderer"<br>OpenGL renderer string: Mesa DRI Intel(R) UHD Graphics 620 (WHL GT2)<br>➜ ~ DRI_PRIME=1 glxinfo | grep "OpenGL renderer"<br>OpenGL renderer string: AMD Radeon Pro WX3100 (POLARIS12, DRM 3.33.0, 5.3.0-53-generic, LLVM 9.0.1)</div><div>```<br></div><div><br></div><div>I
had hoped to configure a four-way multihead configuration (3 monitors
using the dGPU, and the built-in display driven by the iGPU). Alas, this
seems to be impossible with my hardware; the AMD device lacks an output
and merely serves as an offloading device.</div><div>While
investigating this, I came across something I didn't quite understand.
Officially, the Intel UHD 620 supports three displays. However, `xrandr`
shows that there are four CTRCs available on Provider 0 (Intel). </div><div><br></div><div>```</div><div>➜ ~ xrandr --verbose | grep CRTC <br> CRTC: 0<br> CRTCs: 1 0 2<br> CRTCs: 1 0 2<br> CRTC: 1<br> CRTCs: 1 0 2<br> CRTC: 2<br> CRTCs: 1 0 2<br> CRTCs: 1 0 2<br> CRTCs: 1 0 2<br> CRTCs: 1 0 2<br> CRTCs: 3<br></div><div>```</div><div><br></div><div>It seems that the fourth CRTC ("third" when zero-indexed) is used by VIRTUAL1 output.</div><div><br></div><div>```</div>➜ ~ xrandr --verbose | tail<br>VIRTUAL1 disconnected (normal left inverted right x axis y axis)<br> Identifier: 0x6f<br> Timestamp: 22792<br> Subpixel: no subpixels<br> Clones: <br> CRTCs: 3<br> Transform: 1.000000 0.000000 0.000000<br> 0.000000 1.000000 0.000000<br> 0.000000 0.000000 1.000000<br> filter: <br><div>```<br></div><div><br></div><div>Out of curiosity, I thought to move CRTC 3 to a connected but disabled monitor (DP2). However, this doesn't seem to work.</div><div><br></div><div>```</div><div>➜ ~ xrandr --output DP2 --crtc 3 <br>xrandr: output DP2 cannot use crtc 0x67</div><div>```</div><div><br></div><div>After
some Googling, I've come to believe that the VIRTUAL1 output has been
created by the intel-virtual-output utility. To be honest, I find the
man page for this package vague. "The tool connects local VirtualHeads
to a remote output, allowing the primary display to extend onto the
remote outputs."</div><div>I'm admittedly (and probably quite clearly) a
newbie when it comes to graphics, so this description tells me very
little. Moreover, the help menu lists options for starting Bumblebee,
something I believe is Nvidia-specific. Every forum thread I've read
mentioning this utility involves an Nvidia card.<br></div><div><br></div><div>My questions are:</div><div>1. Why or how can I have more CRTCs than officially supported outputs for the Intel UHD 620?</div><div>2. What does the intel-virtual-output utility do for me, a hybrid Intel/AMD user?</div><div>3. Why do I need VIRTUAL1?<br></div><div>4. What would happen if I removed the intel-virtual-output utility?<br></div><div><br></div><div>Thank you in advance,<br></div><div><div dir="ltr"><div dir="ltr"><div><div dir="ltr"><div>Andrew Parsons</div></div></div></div></div></div></div></div></div></div></div></div>