Bug 752593

Created attachment 481765 [details]
output of dmesg while using DisplayPort output

User-Agent:       Mozilla/5.0 (X11; Linux i686; rv:10.0.2) Gecko/20100101 Firefox/10.0.2

The kernel radeon DRM driver produces a video output frequency of
only 3/4 of the requested value on my DisplayPort output. This
happens on the text console without X11 running, but later in the
boot sequence also with X running. My monitor gets blank because it
cannot display 45 Hz instead of 60 Hz. When in X11, a workaround is
to increase the requested frequency to 80 Hz, resulting in 60 Hz
being output. The problem does not occur on the VGA output. The
problem probably does not occur on the LVDS output of my laptop, but
I cannot tell the output frequency there.

Product: openSUSE 12.1
Kernel: Linux shaun 3.1.9-1.4-desktop #1 SMP PREEMPT Fri Jan 27 08:55:10 UTC 2012 (efb5ff4) i686 i686 i386 GNU/Linux
Chipset: "ATI Mobility Radeon HD 3650" (ChipID = 0x9591)
Machine: Lenovo Thinkpad T500, with LVDS monitor built-in, and with
    DisplayPort and VGA video outputs
External Monitor: HP LP2275w

I attach the outputs of dmesg, lsmod, xrandr -q and the log Xorg.0.log
for the cases displayport-* (erroneous) and vga-* (KMS off, no problem)


Reproducible: Always

Steps to Reproduce:
1. boot with external, second monitor on DisplayPort output
2. Grub boot menu is displayed, at 60 Hz
3. boot messages of initial ram disk appear at 60 Hz (splash turned off)
4. boot messages after initial ram disk appear at 45 Hz on DisplayPort
   output and probably normally on LVDS internal monitor
5. X11 login and session appear at 60 Hz on DisplayPort (while xorg.conf
   requests 80 Hz as my workaround), and probably normally on LVDS
   internal monitor
6. switching to text console gives same result as under 4.

Actual Results:  
After initial ram disk, video frequency on DisplayPort output is
only 3/4 of requested value. If I choose other screen
resolution/frequency pairs in X11, it is also always 3/4 of the
frequency requested in the mode line of xorg.conf. No problem occurs
if I use the VGA output. No problem occurs with kernel parameter
"nomodeset", but this switches off the hardware acceleration (which
makes it inacceptably slow).


Expected Results:  
The video output frequency should always be at its nominal value.

With openSUSE 11.3, everything worked for me, including hardware
acceleration, but I had switched off KMS using "nomodeset". This is
not possible anymore with openSUSE 12.1, since this now stops the
hardware acceleration.