[Bug 59785] [dual-gpu regression] Display shuts off when switching to discrete graphics card

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=59785

--- Comment #16 from Daniel Vetter <daniel at ffwll.ch> ---
Hm, that'll break pretty horribly, and I think we're looking at the wrong
things.

Can you play around whether just disabling the callbacks in intel_lvds.c for
these function pointers (and not for all the other encoders helps)? I.e.
something like:

diff --git a/drivers/gpu/drm/i915/intel_lvds.c
b/drivers/gpu/drm/i915/intel_lvds.c
index 8c61876..c1586d3 100644
--- a/drivers/gpu/drm/i915/intel_lvds.c
+++ b/drivers/gpu/drm/i915/intel_lvds.c
@@ -203,6 +203,8 @@ static void intel_disable_lvds(struct intel_encoder
*encoder)
        struct drm_i915_private *dev_priv = dev->dev_private;
        u32 ctl_reg, stat_reg;

+       return;
+
        if (HAS_PCH_SPLIT(dev)) {
                ctl_reg = PCH_PP_CONTROL;
                stat_reg = PCH_PP_STATUS;

If that still works as a workaround, please test whether writing the ctl_reg or
disabling the backlight is the crucial piece.

I guess we just need to drill down until we have the root-cause like that, then
either fix it or apply a quirk. But since you seem to be good at messsing with
the source, that should be doable.

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