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[Success] Radeon RX 6800 XT - Big Sur

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I hope that USB-C port works normally for connecting a monitor to
Currently I'm using the Type-C port on RX6800 FE to drive a LG Ultrafine 4K. The interesting thing is, when I use a USB-C header, the display works fine (both on Windows 10 and macOS Big Sur); but when a Thunderbolt 3 wire is used, there is no display. So, I suppose that port is a micro-DP & USB 3.1/3.2 combined port, something similar with a type-c port on a laptop.
 
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Currently I'm using the Type-C port on RX6800 FE to drive a LG Ultrafine 4K. The interesting thing is, when I use a USB-C header, the display works fine (both on Windows 10 and macOS Big Sur); but when a Thunderbolt 3 wire is used, there is no display. So, I suppose that port is a micro-DP & USB 3.1/3.2 combined port, something similar with a type-c port on a laptop.
Oh that's interesting. I didn't realise there was a difference between Thunderbolt USB-C cables and non-Thunderbolt USB-C.

I bought a couple of cables and adapters the other day, from Amazon. I got a USB-C to Display port adapter, allowing plugging in any normal DP cable into the adapter. And I also got a couple of USB-C to Displayport cables. I think all the cables/adapters I got all said they worked with both USB C and Thunderbolt.

I tried them in the RX6800 USB-C port and they all worked fine with my DP displays in Windows. Haven't tested macOS yet, other than when I confirmed the USB C port was a functioning as a USB port. But yeah, the fact that it does work already as a macOS display surely means it's pretty likely to be fully functional once the drivers are complete.

I got so many cables because my X299 motherboard also has built-in Thunderbolt 3, with Displayport-In ports to allow routing a discrete GPU to Thunderbolt, then using a USB-C to Displayport cable to output the display signal over Thunderbolt. I've tested that too using the same cables/adapter and it works, though it only seems to allow connecting one monitor per connected Displayport In cable, so there's no real benefit to my using it. I'd had a small hope that it might allow me to use more display outputs by running one DisplayPort In cable then using two USB-C to Displayport output cables. For that I think I'd need a proper Thunderbolt hub, and even then I'm not sure if it will work.
 
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I did find it interesting that Apple has the RX 6800 XT device-id 0x73BF1002 in both the AMDRadeonNavi10Controller and AMDRadeonNavi21Controller IOPCIMatch properties.
The kernel log shows this:
Code:
2020-12-24 11:08:43.719470-0500  localhost kernel[0]: (AMDRadeonX6000Framebuffer) <AMDRadeonX6000Framebuffer`AMDRadeonX6000_AmdGpuWrangler::probe(IOService*, int*)> [2:0:0][WRANGLER] AMDRadeonX6000_AmdGpuWrangler::probe !!! FAIL: shouldSupportBoard! device_id:0x73bf, rev_id:0xc1, ss_id:0x439e, ss_vid:0x1da2
IOReg shows picture attached:
 

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Gigamaxx

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I did find it interesting that Apple has the RX 6800 XT device-id 0x73BF1002 in both the AMDRadeonNavi10Controller and AMDRadeonNavi21Controller IOPCIMatch properties.
The kernel log shows this:
Code:
2020-12-24 11:08:43.719470-0500  localhost kernel[0]: (AMDRadeonX6000Framebuffer) <AMDRadeonX6000Framebuffer`AMDRadeonX6000_AmdGpuWrangler::probe(IOService*, int*)> [2:0:0][WRANGLER] AMDRadeonX6000_AmdGpuWrangler::probe !!! FAIL: shouldSupportBoard! device_id:0x73bf, rev_id:0xc1, ss_id:0x439e, ss_vid:0x1da2
IOReg shows picture attached:
Are you getting the same Audio codec? RX 6800

Screen Shot 2020-12-24 at 8.49.23 AM.png
 
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Seems that support is on the way... Big Navi is a worthy upgrade over the prior generation. I'm liking the high FPS.
 
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I wanna add that on my setup with 6800 XT and DP output works well even if its 3440x1440 - laggy without acceleration but no additional glitches etc. But HDMI output doesnt work. I don't know if its cause lack of full support but big sur doesnt even see monitor on HDMI plug.
 
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I randomly impulse bought a 6900xt yesterday (More money than sense) I kind of hoped it would work with Big Sur but guess I am waiting like you guys. HDMI works fine for me in Big Sur without HW acceleration obviously. If anyone has any suggestions or wants me to try anything then i will be happy to give it a go.
 
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No you have not missed anything just a matter of waiting for Apple to support the cards in a future update I am afraid.
 
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Support for 5700XT was added in December of 2019, The iMac you talk about was released in August of 2020... The timing makes no sense if they only had the new iMac in mind.
Uh sure it does, why not complete the work while you build out the new iMac? Sorry but there is no reason for them to upgrade unless they plan to use on in the new iMac or they want eGPU support for Apple Silicon. Not saying it's impossible, just have some doubt.
 
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