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Change input with 2 cards and VGA passthrough

Open v44r opened this issue 6 years ago • 4 comments

I have a BenQ BL2400. The DP-1 input is connected to an Intel GPU, the DVI-1 input is connected to an AMD GPU that I passthrough to a Windows virtual machine.

I'd like to switch inputs with a keyboard shortcut that I have set in the window manager in linux. When I'm in linux (Intel==>DP-1 input selected) I can switch to Windows (AMD GPU==>DVI-1) without problems. This is the output of ddcutil detect while in linux before switching:

# sudo ddcutil detect
Display 1
   I2C bus:             /dev/i2c-6
   EDID synopsis:
      Mfg id:           BNQ
      Model:            BenQ BL2400
      Serial number:    49A02042SL0
      Manufacture year: 2010
      EDID version:     1.4
   VCP version:         2.1

However, while I'm showing Windows (DVI-1) if I run the same command from a linux terminal, I get:

# sudo ddcutil detect
Invalid display
   I2C bus:             /dev/i2c-6
   EDID synopsis:
      Mfg id:           BNQ
      Model:            BenQ BL2400
      Serial number:    49A02042SL0
      Manufacture year: 2010
      EDID version:     1.4
   DDC communication failed

and I cannot switch back with ddcutil. If I switch manually (with the button) to DP-1 and run ddcutil again the following executions are even worse:

# sudo ddcutil detect
No displays found

and I have to turn the monitor off and on to be able to control it again.

Maybe windows is messing with DDC? Is it a bad idea to try to do what I'm doing? Should I search for a windows utility to change back to linux in DP-1 or is it better to not even try to mess with DDC from two running OSs?

v44r avatar Apr 11 '19 11:04 v44r

What you're trying to do sometimes works, sometimes doesn't. It seems to depend on the monitor's DDC/CI implementation - whether DDC communication is active on the inactive video input.

Some things you might try:

  • Avoid using DisplayPort. I2C on DVI and HDMI uses dedicated pins, whereas I2C on DIsplayPort is emulated over the Aux channel.
  • Reference the display by its i2c bus number, e.g. "sudo ddcutil --bus 6 setvcp 60 x0f"
  • Use a Windows program within the VM to switch back

The latter almost always works.  I suggest using softMCCS https://www.entechtaiwan.com/lib/softmccs.shtm from EnTech, at least for testing.  Once you know that works you can look for a simpler Windows command line utility to perform the switching.

One thing that has me a bit perplexed is that there appears to be only 1 monitor (the BL2400) connected to the system.  How are you issuing Linux commands when the monitor is switched to Windows?

If you run command "sudo ddcutil environment --verbose" and send the output as an attachment it will help me better understand your configuration.

Sanford

On 4/11/19 7:25 AM, v44r wrote:

I have a BenQ BL2400. The DP-1 input is connected to an Intel GPU, the DVI-1 input is connected to an AMD GPU that I passthrough to a Windows virtual machine.

I'd like to switch inputs with a keyboard shortcut that I have set in the window manager in linux. When I'm in linux (Intel==>DP-1 input selected) I can switch to DVI-1 (AMD GPU==>Windows) without problems. This is the output of ddcutil detect while in linux before switching:

|# sudo ddcutil detect Display 1 I2C bus: /dev/i2c-6 EDID synopsis: Mfg id: BNQ Model: BenQ BL2400 Serial number: 49A02042SL0 Manufacture year: 2010 EDID version: 1.4 VCP version: 2.1 |

However, while I'm showing Windows (DVI-1) if I run the same command from a linux terminal, I get:

|# sudo ddcutil detect Invalid display I2C bus: /dev/i2c-6 EDID synopsis: Mfg id: BNQ Model: BenQ BL2400 Serial number: 49A02042SL0 Manufacture year: 2010 EDID version: 1.4 DDC communication failed |

and I cannot switch back with ddcutil. If I switch manually (with the button) to DP-1 and run ddcutil again the following executions are even worse:

|# sudo ddcutil detect No displays found |

and I have to turn the monitor off and on to be able to control it again.

Maybe windows is messing with DDC? Is it a bad idea to try to do what I'm doing? Should I search for a windows utility to change back to linux in DP-1 or is it better to not even try to mess with DDC from two running OSs?

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rockowitz avatar Apr 11 '19 18:04 rockowitz

Thanks for the tips.

One thing that has me a bit perplexed is that there appears to be only 1 monitor (the BL2400) connected to the system. How are you issuing Linux commands when the monitor is switched to Windows?

I can change the keyboard focus from linux to windows and vice-versa pressing both Ctrl keys. So even when I'm showing windows I can (blindly) run linux commands. I run the command, nothing happens, so I switch inputs with the physical button and see the resulting error.

I tried switching DP and DVI (i.e. using DVI for linux and DP for windows) and using the bus number instead of the display number (/dev/i2c-4 right now), but I get the same result: when I change from linux (DVI) to windows (DP) no errors:

$ sudo ddcutil -b 4 setvcp 60 0x0f
$

and the monitor switches inputs accordingly. But when I try to switch back (I'm showing windows but linux has keyboard focus, so I run this blind):

$ sudo ddcutil -b 4 setvcp 60 0x03
DDC communication failed for monitor on I2C bus /dev/i2c-4
$

So, as you say, it seems that the monitor ignores DCC commands from non-selected inputs. With environment verbose, when the input connected to the linux graphics card is selected (currently DVI):

 Trying simple VCP read of feature 0x10...
      read() returned 6e 88 02 00 No protocol specified
10 00 00 64 00 1e de
      Attempt 1 to read feature succeeded.
      DDC communication succeeded

but when another input is selected:

Trying simple VCP read of feature 0x10...
      read() returned de de de de No protocol specified
de de de de de de de
      Attempt 1 to read feature failed. status = DDCRC_DDC_DATA(-3001): DDC data error.  Retrying...
      read() returned de de de de de de de de de de de
      Attempt 2 to read feature failed. status = DDCRC_DDC_DATA(-3001): DDC data error.  Retrying...
      read() returned de de de de de de de de de de de
      Attempt 3 to read feature failed. status = DDCRC_DDC_DATA(-3001): DDC data error.
      DDC communication failed.

I ended up installing ClickMonitorDDC in windows, which has a nice interface and support for hotkeys and assigned a combination to switch back to linux. Now I can switch back and forth without problems.

(edit) full log

v44r avatar Apr 12 '19 10:04 v44r

Thanks for the update.  I'm glad you got it working.

Can I ask you to run "sudo ddcutil interrogate" and send me the output as a file?  I'd like to add a description of your monitor to the list at http://www.ddcutil.com/monitor_notes/

Sanford

On 4/12/19 6:20 AM, v44r wrote:

Thanks for the tips.

One thing that has me a bit perplexed is that there appears to be
only 1 monitor (the BL2400) connected to the system. How are you
issuing Linux commands when the monitor is switched to Windows?

I can change the keyboard focus from linux to windows and vice-versa pressing both Ctrl keys. So even when I'm showing windows I can (blindly) run linux commands. I run the command, nothing happens, so I switch inputs with the physical button and see the resulting error.

I tried switching DP and DVI (i.e. using DVI for linux and DP for windows) and using the bus number instead of the display number (/dev/i2c-4 right now), but I get the same result: when I change from linux (DVI) to windows (DP) no errors:

|$ sudo ddcutil -b 4 setvcp 60 0x0f $ |

and the monitor switches inputs accordingly. But when I try to switch back (I'm showing windows but linux has keyboard focus, so I run this blind):

|$ sudo ddcutil -b 4 setvcp 60 0x03 DDC communication failed for monitor on I2C bus /dev/i2c-4 $ |

So, as you say, it seems that the monitor ignores DCC commands from non-selected inputs. With environment verbose, when the input connected to the linux graphics card is selected (currently DVI):

|Trying simple VCP read of feature 0x10... read() returned 6e 88 02 00 No protocol specified 10 00 00 64 00 1e de Attempt 1 to read feature succeeded. DDC communication succeeded |

but when another input is selected:

|Trying simple VCP read of feature 0x10... read() returned de de de de No protocol specified de de de de de de de Attempt 1 to read feature failed. status = DDCRC_DDC_DATA(-3001): DDC data error. Retrying... read() returned de de de de de de de de de de de Attempt 2 to read feature failed. status = DDCRC_DDC_DATA(-3001): DDC data error. Retrying... read() returned de de de de de de de de de de de Attempt 3 to read feature failed. status = DDCRC_DDC_DATA(-3001): DDC data error. DDC communication failed. |

I ended up installing ClickMonitorDDC in windows, which has a nice interface and support for hotkeys and assigned a combination to switch back to linux. Now I can switch back and forth without problems.

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rockowitz avatar Apr 15 '19 12:04 rockowitz

im having this same issue: host: manjaro guest: win 10 with dedicated gtx 660 passed through

my issue is that i cant switch back from windows via ClickMonitorDDC or softMCCS which says it cant find DCC/CI: softMCCS.log

interrogate log: ddcutil-interrogate.log

kinghat avatar Aug 02 '20 21:08 kinghat