Display Port -> HDMI and Haiku

So I purchased a new 27" QHD monitor (2560x1440) from Dell, and later on discovered that it has USB-C connector, and 2 HDMI inputs (sadly, no Display Port). The Radeon 5600XT has Display port and HDMI. The only cables I have are DP->DP, USB-C → USB-C, and DP->HDMI (1.4). The only combination that works is DP->HDMI. So lets test it:

So under Haiku and VESA drivers, the monitor comes up nicely as 2560x1440. Yay Haiku, works like a charm. I can even set refresh rates to 75Hz. All is good with VESA driver in Haiku.

Under both Windows 11 and Linux Mint, the monitor is restricted to 2048x1080. Obviously the AMD driver doesn’t like something with the HDMI cable (rated 1.4). So it drops the resolution to this weird resolution.

So I’m fuming right now that the big boys cannot get the driver right for this combination, yet with VESA it obviously works. And I need to order another cable combination (probably DisplayPort out to USB-C in). Rage mode ON.


Did you try to select manually the resolution:

HDMI 1.4 is the problem. Buying a HDMI 2.0 cable resolved the issue. With AMD adrenaline drivers, you can set custom resolutions and frequencies, but that didn’t work (Dell has actual EDID parameters in user manual, and even monitor drivers).

Anyhow, Haiku VESA driver worked perfectly with the DP->HDMI 1.4 cable. The Win/Linux AMD driver is the culprit here.

1 Like

The link explains that it’s possible to reduce the required pixel clock for such a resolution, see the mode 2560x1440R with HDMI 1.4 too.

Thanks Korli, I got a $10 HDMI 2.0 cable and it just works (both Linux and Win). I just wanted to post the positive experience I had with Haiku, since in this scenario the most simple driver (VESA) worked while the more complex drivers (AMDGPU and Radeon Adrenaline) failed to drive the monitor correctly. As you pointed out, the fact that it worked with Haiku indicates that it should have also worked with the mainstream OS’s, but the driver developers chose to exclude the higher resolutions, for reasons only known to them. All is good now.