XFX r7-250a-lzh4 not displaying 3840x2160 @ 30Hz over HDMI

[Alex Deucher]

On Tue, Feb 18, 2014 at 5:28 AM, Adam Richter
<adam_richter2004 at yahoo.com> wrote:
> The XFX Radeon r7-240a-clh4 and XFX Radeon r7-250a-zlh4 video cards do not seem to be able to generate 3840x2160 @ 30 Hz video modes over HDMI, even though I believe their hardware is supposed to be capable of this (~299 MHz pixel clock).
>
> At least with my se39uy04 39" Seiki television, the Radeon X.org driver happily passed through the five 3840x2160 @ 24-30 Hz that the television's advertises in its EDID modes to xrandr, meaning that driver thinks it can support those video modes, but, if I select any of them, the telvision just says "mode not support."  In comparison, if I make a custom video mode for 3840x2160 @ 15Hz, the 4k TV displays that fine.
>

Please file a bug (https://bugs.freedesktop.org, product DRI,
component DRM/Radeon) and attach your dmesg output and xorg log.

> I observed this problem with the r7-240 and r7-250 on Linux 3.13.0-x86_64, and with the r7-250 on Linux-3.14-rc3-x86_64 (I haven't tried the r7-240 on it).
>
>
> I am reporting this bug now primarily in the hopes that doing so might eventually benefit other users.  As for my own use, it looks like I'm probably not going to use either of these video cards anyhow, because they appear not to support dual link, contrary to Tiger Direct's description fo the r7-250 card, by the way (yes, I tried faking dual link connector information in atombios.c).  That said, I am happy to do further experiments with these cards if that would be helpful.
>

They support duallink DVI just fine assuming the oem has wired them up
such that they can be used.  Oland chips (R7 240, R7 250) only have 2
digital links so if you want duallink DVI, both would have to be used
for DVI which not leave any links for other connectors.  If you board
has more than one digital connector, it's probably single link.  Most
other SI and CI chips support 6 digital links.

Alex