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4K60 4:4:4 10-bit on Mac Pro 5,1 AMD RX480

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Apr 3, 2022
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Motherboard
2012 Mac Pro 5,1
CPU
Dual 3.46GHz 6-core Intel Xeon
Graphics
AMD RX480
I'm having an issue achieving 4K resolution at 60Hz with chroma 4:4:4 and 10-bit color. I've spent countless hours reading through various posts on many different forums and testing possible solutions, but have drawn a blank.

I'm running Mac OS 12.3.1 (Monterey) on a 2012 Mac Pro 5,1 using OpenCore and WhateverGreen. I'm using an AMD RX480 8GB card (and have an identical secondary card that I've tested with). My display is an LG C1 OLED. The card supports DisplayPort 1.4 and HDMI 2.0b. The display supports HDMI 2.1.

I believe that I've eliminated cable issues from the equation. I have tested running HDMI from the card to the display with an HDMI 2.1 cable, using a DP 1.4 to HDMI 2.1 cable (this one, which I believe is an active adapter, although I have been unable to confirm) from the card's DisplayPorts to the display's HDMI ports, using this active DP 1.4 to HDMI 2.1 adapter in combination with an HDMI 2.1 cable, and using this active DP to HDMI 2.0 adapter.

I have been able to get 4k60 YCbCr 4:4:4 with 8-bit color, 4k30 YCbCr 4:4:4 with 10-bit color, 4k60 YCbCr 4:2:0 with 10-bit color, 4k60 RGB 4:4:4 with 8-bit color, but in no event have I achieved 4k60 YCbCr 4:4:4 with 10-bit color or 4k60 RGB 4:4:4 with 10-bit color. HDR also functions in at least the 10-bit modes.

The card, display, and cables are all capable of outputting, transmitting, and displaying 4k60 4:4:4 at 10-bits, and likely at 4k120 from what I can discern.

According to my research, 4K60 4:4:4 10b-HDR = 22.28Gbps, which is outside of the range for HDMI 2.0b at ~18Gbps, so I can eliminate outputting a signal from the card's HDMI port (unless using DSC, which I believe lowers the 22.28Gbps back to ~18Gbps, possibly lower?), leaving me with just the DisplayPort 1.4 outputs. The DP1.4 to HDMI 2.1 cable claims to support 4k120 HDR, which should consume around ~24Gbps at 4:2:0, and the other DP1.4 to HDMI 2.1 active adapter with HDMI 2.1 cable claims to support 4k120 and 8k60 HDR, which should consume ~40Gbps. The active adapter's product page clearly states that it is capable of 4k60 4:4:4 at 10-bits:

  • Operation mode 8K4K @60Hz with 10bpc, YUV420, DP: 4-lane HBR3, HDMI: FRL 10G, HDR10, and DSC (Dec) - 1,500 mW
  • 8K4K @60Hz with 10bpc, RGB/YUV444, DP: 4-lane HBR3, HDMI: FRL 6G, HDR10, and DSC (Passthrough) - 1,100 mW
  • 4K2K @120Hz with 10bpc, RGB/YUV444, DP: 2-lane HBR3, HDMI: FRL 10G, HDR10, and DSC (Dec) - 1,100 mW
  • 4K2K @60Hz with 8bpc, RGB/YUV444, DP: 4-lane HBR2, HDMI: TMDS 6G, SDR - 780 mW

Running AGDCDiagnose -apwd lists the link rate over the DP1.4 to HDMI 2.1 cable as 8100Mbps with four link lanes. The output from the command also states:

Reg: 002200: 14 : DPCD_REV: 1.4

Reg: 002201: 1e : MAX_LINK_RATE: HBR3

Reg: 002202: c4 : MAX_LANE_COUNT: 4, TPS3_SUPPORTED: 1, ENHANCED_FRAME_CAP: 1

So it seems that adequate bandwidth is available to support 4k60 4:4:4 at 10-bits unless I'm missing something somewhere. I'm attaching the complete output from the AGDCDiagnose command.

I've tried changing the device id of the card in WhateverGreen in order to see if the OS was somehow limiting the display card's output due to the model, but trying various other device ids with Polaris chips (and even some others) has yielded nothing different. I've also attempted setting or changing several other parameters in WhateverGreen, such as the "enable-dpcd-max-link-rate-fix," setting "dpcd-max-link-rate" to "HgAAAA==" (0x1E000000), and the "enable-hdmi20" flag, among others, but all to no avail.

I've spent time playing with the EDIDUtil created by @joevt along with the more simplified patch-edid script to see if limiting the EDID to RGB mode only would solve the issue, but it simply allows for 4k60 RGB 4:4:4 at 8-bits.

Hoping that someone can point me in the right direction. I'm also going to include my OpenCore config.plist in case that is of any help. Happy to attach output from any additional commands if that would assist.
 

Attachments

  • AGDCDiagnose1.txt.zip
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  • config.plist.zip
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i am using macOS Ventura with RX6900 XT + LG C2 42.
but i can get 4K 120hz only with ycbcr420 8bit. and no HDR.

if i switch to 4K 60hz, LG shows ycbcr420 10bit and with HDR.

for hdmi 2.1, still dont know how to get 4k 60hz with full RGB + HDR
 
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