[RX560] 10bit (1080p) reported over HDMI, but delivering 8 bit

[pinktank]

Hello all,
I have a couple displays (NEC PA243W and EIZO CS2420) that get a 8bit signal (you can see stepped gradients) if I connect them via HDMI rather than DP. Sytem report shows 10 bit (ARGB101010) still but they are definitely not operating in 10. Was wondering if anybody had any idea.

 

I know that with 4K I would have to adjust 4:2:2 for bandwidth but this is plain old 1080p. Again, displayport works as intended, and I can swap the DP/HDMI and both monitors have the same issue.

Do I need a framebuffer patch on the rx560?

 

This is Mojave, with Whatevergreen, IGPU enabled but headless, Imac 18,3
 

CS2420:
  Resolution:    1920 x 1200 (WUXGA - Widescreen Ultra eXtended Graphics Array)
  UI Looks like:    1920 x 1200
  Framebuffer Depth:    30-Bit Color (ARGB2101010)
  Main Display:    Yes
  Mirror:    Off
  Online:    Yes
  Rotation:    Supported
  Automatically Adjust Brightness:    No
  Connection Type:    DisplayPort
PA243W:
  Resolution:    1920 x 1200 (WUXGA - Widescreen Ultra eXtended Graphics Array)
  UI Looks like:    1920 x 1200 @ 60 Hz
  Framebuffer Depth:    30-Bit Color (ARGB2101010)
  Display Serial Number:    xxxxxxxxx
  Mirror:    Off
  Online:    Yes
  Rotation:    Supported
  Automatically Adjust Brightness:    No

Edited November 12, 2019 by pinktank

[pinktank]

Anyone?

[Slice]

It is normal. System uses 10bits per color but output is 8bit with dithering.

[jinbingmao]

It looks like the monitor doesn't support it

[pinktank]

Wrong on both counts, the display certainly supports 10 bits over HDMI and DP both, and the system can output 10bpc in general (as it does in DP) unless there is a new limitation/bug with hdmi.

[martin953]

TS is right. Had absolutely the same issue. Two 4k LG's on RX 460: one over DP and another over HDMI. Never got to calibrate them equally and whenever I turned 10bit via HDMI I got banding.

Had to switch to RX 480 with two DP's.