[Bug 16389] New PM-Code produces white screen on laptop display on startup on an radeon x700

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=16389





--- Comment #5 from Alex Deucher <alexdeucher@gmail.com>  2010-07-20 16:08:48 ---
(In reply to comment #4)
> Looking at fdo-bug 22755 i found another way to put the screen into an usable
> stae after resolution switch:
> xrandr -s 1024x768; xrandr --output LVDS --off; xrandr --output LVDS --auto
> works (i think it is the same call as vbetool dpms off / on).
> Without turning the output off and on i get the white screen. Whats the
> difference between boot-time initialization of the screen (which does not work)
> and the initialization with the xrandr off / on call (which works) ?

Nothing.  Both use the same path in the driver.  I suspect this is a timing
issue with the LVDS.  Your system probably needs a longer/shorter delay
somewhere in the LVDS dpms code.  Can you try adjusting the delays in
radeon_legacy_lvds_dpms() in radeon_legacy_encoders.c?  Can you also try
something like this:

diff --git a/drivers/gpu/drm/radeon/radeon_legacy_encoders.c
b/drivers/gpu/drm/radeon/radeon_legacy_encoders.c
index bad77f4..5688a0c 100644
--- a/drivers/gpu/drm/radeon/radeon_legacy_encoders.c
+++ b/drivers/gpu/drm/radeon/radeon_legacy_encoders.c
@@ -108,6 +108,7 @@ static void radeon_legacy_lvds_dpms(struct drm_encoder
*encoder, int mode)
                udelay(panel_pwr_delay * 1000);
                WREG32(RADEON_LVDS_GEN_CNTL, lvds_gen_cntl);
                WREG32_PLL(RADEON_PIXCLKS_CNTL, pixclks_cntl);
+               udelay(panel_pwr_delay * 1000);
                break;
        }

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