[Intel-gfx] [PATCH 2/7] drm/i915: Resolving the memory region conflict for Stolen area

[akash.goel at intel.com]

From: Akash Goel <akash.goel at intel.com>

There is a conflict seen when requesting the kernel to reserve
the physical space used for the stolen area. This is because
some BIOS are wrapping the stolen area in the root PCI bus, but have
an off-by-one error. As a workaround we retry the reservation with an
offset of 1 instead of 0.

v2: updated commit message & the comment in source file (Daniel)

Signed-off-by: Akash Goel <akash.goel at intel.com>
---
 drivers/gpu/drm/i915/i915_gem_stolen.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
index 1a24e84..114a806 100644
--- a/drivers/gpu/drm/i915/i915_gem_stolen.c
+++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
@@ -82,9 +82,23 @@ static unsigned long i915_stolen_to_physical(struct drm_device *dev)
 	r = devm_request_mem_region(dev->dev, base, dev_priv->gtt.stolen_size,
 				    "Graphics Stolen Memory");
 	if (r == NULL) {
-		DRM_ERROR("conflict detected with stolen region: [0x%08x - 0x%08x]\n",
-			  base, base + (uint32_t)dev_priv->gtt.stolen_size);
-		base = 0;
+		/*
+		 * One more attempt but this time requesting region from
+		 * base + 1, as we have seen that this resolves the region
+		 * conflict with the PCI Bus.
+		 * This is a BIOS w/a: Some BIOS wrap stolen in the root
+		 * PCI bus, but have an off-by-one error. Hence retry the
+		 * reservation starting from 1 instead of 0.
+		 */
+		r = devm_request_mem_region(dev->dev, base + 1,
+					    dev_priv->gtt.stolen_size - 1,
+					    "Graphics Stolen Memory");
+		if (r == NULL) {
+			DRM_ERROR("conflict detected with stolen region:"\
+				  "[0x%08x - 0x%08x]\n",
+				  base, base + (uint32_t)dev_priv->gtt.stolen_size);
+			base = 0;
+		}
 	}
 
 	return base;
-- 
1.8.5.2