[Bug 49193] random screen blackouts

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=49193

--- Comment #3 from Alex Deucher <agd5f at yahoo.com> 2012-04-26 20:40:25 UTC ---
(In reply to comment #2)
> radeon.disp_priority=2 has no effect at all. As I wrote, the problem goes away
> if I disable h/w acceleration in the radeon driver, or switch to the fbdev
> driver. The video resolution and timing are the same in all cases. Is this
> consistent with the theory of the pixel clock being too high?

It's consistent with underflow to the display controller.  The memory
controller on the GPU has to service several clients (displays, 3D engine, 2D
engine, etc.).  When you enable acceleration, the 2D and 3D engines are active
and contend with the display controllers for bandwidth in the memory
controller.  If the memory controller not able to service the display fifo in
time, it will run dry causing the blankout you see.  Disabling acceleration
takes the 2D and 3D engines out of contention so the memory controller only has
to worry about filling display requests.  A lower resolution mode will also
probably help since the bandwidth requirements are lower.  A 1920x1080 mode
with a lower refresh rate may also help since the bandwidth requirements would
also be lower (assuming your monitor will accept it).

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