Bug#661943: xserver-xorg-video-radeon: Unable to set native resolution with KMS enabled

[Christopher Dow]

I did some more digging in to this and it appears that the reason that I am getting the 'invalid mode' error is that the refresh rate the monitor is receiving is not the refresh rate configured by X or the framebuffer.

I noticed that my monitors report what resolution and refresh rate they are receiving.  If X or the framebuffer are configured with a refresh rate of 75Hz then the monitor is reporting that it receives a refresh rate of 56Hz (which is at the bottom of the range supported by my monitors).  Refresh rates of 70Hz produce an output of 52Hz (which still works but is not supported).  I assume that 60Hz is producing an even lower output frequency (hence the 'invalid mode').

If I disable KMS then the reported frequency matches the configured frequency.  

After realizing this, I am able to get the native resolution to display by cofiguring it with a higher refresh rate.

I have no idea why the output frequency doesn't match the configured frequency with KMS.  I assume this is a kernel driver bug, unless there is some configuration I am missing.

-Chris