[Bug 60523] Radeon DPM not working with 2 monitors attached to Radeon HD5770 (Juniper)

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=60523

--- Comment #26 from Alex Deucher <alexdeucher at gmail.com> ---
In order to switch the mclk, the hw needs at least 450us.  The vblank period of
the 1600x1200 mode is 396us, so it's not long enough to switch.  The switch has
to happen during vblank to avoid seeing a flicker when the mclk changes.  As
such the driver picks a power state where the mclk doesn't change (the same
power state that is used for multi-head).  You could try specifying a 1600x1200
modeline with a longer vblank period if you want to use that mode and still
support mclk switching.

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