Trying to port sitronix,st7701 panel driver but nothing shows on display

[Michał Iwanicki]

Hello,

I have a question about porting MIPI DSI panel driver (sitronix,st7701) from Linux to U-Boot (I'm using custom board 
with embedded rk3566 SoM.
I think I'm mostly done, though I had to apply Dang Huynh VOP2 patches (sent to mailing list on Thu Jan 16)
to get anything probed (dw-mipi-dsi-rockchip, dw_mipi_dsi, panel itself).
I don't see any errors in debug output, I made sure that init function in panel driver is called,
'dm tree' shows that required drivers were probed and backlight is on

  video         0  [ + ]   rk3568_vop            |-- vop at fe040000
  vidconsole    0  [ + ]   vidconsole0           |   `-- vop at fe040000.vidconsole0
  video_brid    0  [ + ]   dw-mipi-dsi-rockchip  |-- dsi at fe060000
  dsi_host      0  [ + ]   dw_mipi_dsi           |   |-- dsihost
  panel         0  [ + ]   sitronix_st7701       |   `-- panel at 0

but I don't have any output on display (just black screen).
I know that connection is OK as I can send commands e.g. ALLPON (All Pixel ON) to turn all pixels white but I'm kinda 
stuck how to debug why I see nothing on display. Could anyone direct me how can I debug this further?
Could maybe lack of rockchip,rk3568-iommu (vop_mmu node) drivers be a problem? Maybe I need to modify device-tree
related to display to work with U-Boot?

Best regards,
Michał Iwanicki