[PATCH 2/7] drm/i915: don't use the first stolen page on Broadwell

Paulo Zanoni
2015-09-23T15:52:40Z

The spec says we just can't use it.

v2:
- Add WA name (Ville).
- Add a big comment explaining that we still didn't fix the problem
where we inherit a framebuffer on the first page (Chris, Ville).

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
---
drivers/gpu/drm/i915/i915_gem_stolen.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
index 55df6ce..b11d069 100644
--- a/drivers/gpu/drm/i915/i915_gem_stolen.c
+++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
@@ -51,6 +51,11 @@ int i915_gem_stolen_insert_node_in_range(struct drm_i915_private *dev_priv,
if (!drm_mm_initialized(&dev_priv->mm.stolen))
return -ENODEV;

+ /* See the comment at the drm_mm_init() call for more about this check.
+ * WaSkipStolenMemoryFirstPage:bdw,chv (incomplete) */
+ if (INTEL_INFO(dev_priv)->gen == 8 && start < 4096)
+ start = 4096;
+
mutex_lock(&dev_priv->mm.stolen_lock);
ret = drm_mm_insert_node_in_range(&dev_priv->mm.stolen, node, size,
alignment, start, end,
@@ -393,7 +398,17 @@ int i915_gem_init_stolen(struct drm_device *dev)
dev_priv->gtt.stolen_usable_size = dev_priv->gtt.stolen_size -
reserved_total;

- /* Basic memrange allocator for stolen space */
+ /*
+ * Basic memrange allocator for stolen space.
+ *
+ * TODO: Notice that some platforms require us to not use the first page
+ * of the stolen memory but their BIOSes may still put the framebuffer
+ * on the first page. So we don't reserve this page for now because of
+ * that. Our current solution is to just prevent new nodes from being
+ * inserted on the first page - see the check we have at
+ * i915_gem_stolen_insert_node_in_range(). We may want to fix the fbcon
+ * problem later.
+ */
drm_mm_init(&dev_priv->mm.stolen, 0, dev_priv->gtt.stolen_usable_size);

return 0;
--
2.5.1