Sapphire R9 280 + U28D590 on Yosemite

[ilcasa91]

Hi everyone!
I've just replaced my old GT610 with a great Sapphire R9 280 (http://www.sapphiretech.com/presentation/product/product_index.aspx?pid=2194&lid=1), outputting to a Samsung u28d590 via Displayport 1.2.
It almost worked OOB, I just had to modify the EFI partition in order to avoid boot0 error, following the guide on this forum. My build: Gigabyte GA-Z77-DS3H, i5 3470, 8GB RAM, SSD Samsung 840 EVO 120GB.
No problem with 4k@60Hz: no lag, no flickers, really awesome.
But here's the big question: when I boot, the max resolution I can select is 2560x1440 (from Display preferences -> Display -> Scaled); if, after booting, I unplug and plug in again the displayport cable, then Yosemite suddenly realize that my display can go further and allows me to set 3840x2160.
That's not a big problem, but it's annoying...any ideas about how to boot directly with 3840x2160?
Thank you very much

 

[Stork]

Did you try Display preferences -> Display -> Best for Display?

If that didn't work, try selecting Option key / Scaled. More options should be available.

 

[ilcasa91]

Already tried..both Best for Display and Scaled give me a max resolution of 2560x1440, until I unplug and plug in again the display...this makes the option in the scaled section change and allows me to select 3840x2160. It seems that Yosemite can't detect well my display when I boot, and it has to re-detect it once booted.
I've also tried alt+Detect in the Display Preferences window to force osx to re-detect the monitor "via software", no luck: the only way is phisically unplug and replug.

 

[ismithers]

Already tried..both Best for Display and Scaled give me a max resolution of 2560x1440, until I unplug and plug in again the display...this makes the option in the scaled section change and allows me to select 3840x2160. It seems that Yosemite can't detect well my display when I boot, and it has to re-detect it once booted.
I've also tried alt+Detect in the Display Preferences window to force osx to re-detect the monitor "via software", no luck: the only way is phisically unplug and replug.

I have this issue too. Did you ever find a solution to it? I have the same hardware as you as well.

 

[ilcasa91]

Nope, I'm just keeping unplugging and plugging everytime I boot. Very annoying.