No monitor detected on bus when using an MST Hub

[spyfly]

Describe the bug One of the monitors on the MST-Hub does not get detected, due to a bus being unable to process the same command in parallel.

The solution would be to not read the bus simultaneously, but after each other.

To Reproduce Steps to reproduce the behavior: Connect two Monitors behind a MST-Hub

Journal logs

display-brightness-ddcutil extension:
ddcutil brief info:
Display 1
   I2C bus:  /dev/i2c-17
   Monitor:             RTK:RTK FHD:J257M96B00FL

Display 2
   I2C bus:  /dev/i2c-19
   Monitor:             AUS:ROG PG27U:#ASMNay5aJgbd

Phantom display
   I2C bus:  /dev/i2c-20
   Monitor:             GSM:LG Ultra HD:

Display 3
   I2C bus:  /dev/i2c-21
   Monitor:             GSM:LG Ultra HD:

Display 4
   I2C bus:  /dev/i2c-22
   Monitor:             GSM:LG Ultra HD:

display-brightness-ddcutil extension:
ddcutil brief info found bus line:
    I2C bus:  /dev/i2c-17
display-brightness-ddcutil extension:
ddcutil reading display state for bus: 17
display-brightness-ddcutil extension:
ddcutil brief info found bus line:
    I2C bus:  /dev/i2c-19
display-brightness-ddcutil extension:
ddcutil reading display state for bus: 19
display-brightness-ddcutil extension:
ddcutil brief info found bus line:
    I2C bus:  /dev/i2c-20
display-brightness-ddcutil extension:
ddcutil reading display state for bus: 20
display-brightness-ddcutil extension:
ddcutil brief info found bus line:
    I2C bus:  /dev/i2c-21
display-brightness-ddcutil extension:
ddcutil reading display state for bus: 21
display-brightness-ddcutil extension:
ddcutil brief info found bus line:
    I2C bus:  /dev/i2c-22
display-brightness-ddcutil extension:
ddcutil reading display state for bus: 22
display-brightness-ddcutil extension:
ddcutil reading display status for bus: 20 is: DDC communication failed for monitor on bus /dev/i2c-20

display-brightness-ddcutil extension:
ddcutil reading display status for bus: 21 is: No monitor detected on bus /dev/i2c-21

display-brightness-ddcutil extension:
ddcutil reading display status for bus: 22 is: VCP D6 SNC x01

display-brightness-ddcutil extension:
ddcutil reading display status for bus: 17 is: VCP D6 ERR

display-brightness-ddcutil extension:
ddcutil reading display status for bus: 19 is: VCP D6 ERR

display-brightness-ddcutil extension:

Screenshots If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: Ubuntu
• Version 22.04
• GNOME version 42.5
• Extension version 31

Additional context Add any other context about the problem here.

[spyfly]

Seems to be resolved in Version 33

[spyfly]

Still seems to be an issue, even in Version 33

[daitj]

Let discuss about this issue in #87