Commit d46b60a2 authored Oct 15, 2020 by Ville Syrjälä Committed by Chris Wilson Oct 15, 2020

drm/i915: Mark ininitial fb obj as WT on eLLC machines to avoid rcu lockup during fbdev init



Currently we leave the cache_level of the initial fb obj
set to NONE. This means on eLLC machines the first pin_to_display()
will try to switch it to WT which requires a vma unbind+bind.
If that happens during the fbdev initialization rcu does not
seem operational which causes the unbind to get stuck. To
most appearances this looks like a dead machine on boot.

Avoid the unbind by already marking the object cache_level
as WT when creating it. We still do an excplicit ggtt pin
which will rewrite the PTEs anyway, so they will match whatever
cache level we set.

Cc: <stable@vger.kernel.org> # v5.7+
Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2381


Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20201007120329.17076-1-ville.syrjala@linux.intel.com
Link: https://patchwork.freedesktop.org/patch/msgid/20201015122138.30161-1-chris@chris-wilson.co.uk

parent 4d8a5cfe

drivers/gpu/drm/i915/display/intel_display.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -3433,6 +3433,14 @@ initial_plane_vma(struct drm_i915_private *i915,
		if (IS_ERR(obj))
		return NULL;

		/*
		* Mark it WT ahead of time to avoid changing the
		* cache_level during fbdev initialization. The
		* unbind there would get stuck waiting for rcu.
		*/
		i915_gem_object_set_cache_coherency(obj, HAS_WT(i915) ?
		I915_CACHE_WT : I915_CACHE_NONE);

		switch (plane_config->tiling) {
		case I915_TILING_NONE:
		break;

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