[Bug 61457] [Intel G45] Screen turns blank when terminating a low res X server on a different low res KMS mode.

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=61457

--- Comment #5 from Egbert Eich <eich at pdx.freedesktop.org> ---
(In reply to comment #4)
> 
> in order to set the WM to a constant value and disable the low-power
> switching.

Hrm, right - WM == 'watermarks'. Darn acronyms :(

Ok, I've looked into this - it looks promising.

It is this code path that is causing the problems:

        if (single_plane_enabled(enabled) &&
            g4x_compute_srwm(dev, ffs(enabled) - 1,
                             sr_latency_ns,
                             &g4x_wm_info,
                             &g4x_cursor_wm_info,
                             &plane_sr, &cursor_sr)) {
                I915_WRITE(FW_BLC_SELF, FW_BLC_SELF_EN);
       } ...

The problem occurs when the FW_BLC_SELF_EN bit is set after it has been unset
before.
The reason why the issue doesn't occur for larger modes seems to be that
g4x_compute_srwm() will return false for those.

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