radeon vs radeonhd drivers

[Alex Deucher]

On Mon, Nov 10, 2008 at 10:15 PM, Gene Heskett <gene.heskett at verizon.net> wrote:
> On Monday 10 November 2008, Gene Heskett wrote:
>>Greetings all;
>>
>>I rebuilt 2.6.26 for smp and my new hardware and have rebooted to it.
>>
>>But the monitor is still sitting in black, not powered down, the next
>> morning. This did work well when the box was an xp2800 and the card was an
>> ATI 9200SE AGP version.  I was using the radeon driver in my xorg.conf
>> then.
>>
>>Now the box is a 4 core phenom and the card is an HD2400, PCI-E, and I'm
>> using the radeonhd driver although the radeon seems usable too although
>> slightly slower.
>>
>>Is this driver difference causing the lack of monitor power control?
>>Something that radeonhd does not yet support?
>>
>>Thanks.
>
> Never mind, the answer is yes, monitor powerdown works using the radeon
> driver, but doesn't using the radeonhd driver.
>
> But its not that simple either, cuz when running the radeon driver, I get
> random screen blanking for 1-10 seconds at a time, and for a change it
> doesn't seem to be tied to the time of day since its doing it right now and
> it is 10 pm.

you might try enabling (or disabling depending on the version of the
driver) coherent mode:
xrandr --output <output> --set coherent_mode <0/1>

Alex