Oookay, page 19 of the DCS guide is interesting.
According to a flowchart, a MIPI display is in sleep mode after the initialization sequence.
And according to MIPI, sleep mode is: "In Sleep mode, the display module does not show any image data. In addition, the display interface shall remain powered and along with those functional blocks necessary to maintain the data in the frame memory and registers. The remaining functional blocks are placed in their low power modes. See section 6.5 for a description of Sleep mode."
So yeah, if we just initialized the display without leaving sleep mode, the display shouldn't show any picture at all.
Did we ever exit the sleep mode? (according to DCS, exiting sleep mode is hex code 11h)
get_power_mode (0Ah) is probably interesting as well - as it tells us whether the display is idle, in sleep mode, powered off, etc. (refer to page 58 of the DCS specs)
The result are bits that are encoded to Hex - impossible to read that without the DCS Specs guide, so that really should be helpful!