[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
as somehow the start/base location of the Parent region
of Stolen area which is PCI Bus 0000:00 is not coinciding with
the start of Stolen area and is conflicting with it. For ex.
from the device memory map info provided by '/proc/iomem',
we have seen that somehow a region of PCI Bus 0000:00 is being
shown to start from 0x7b000001,
i.e. (7b000001-ffffffff : PCI Bus 0000:00) & not from
0x7b000000. And the stolen base is coming as 0x7b000000,
thus there is a conflict & stolen area remains unused by driver.
So to circumvent this issue we adjust the base of stolen area by
1 byte when registering it with the kernel.
Otherwise if we don't resolve this conflict or don't remove the
conflict error check from the driver, the stolen area will remain
disabled.

Signed-off-by: Akash Goel <akash.goel at intel.com>
---
 drivers/gpu/drm/i915/i915_gem_stolen.c | 27 ++++++++++++++++++++++++---
 1 file changed, 24 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..29b3693 100644
--- a/drivers/gpu/drm/i915/i915_gem_stolen.c
+++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
@@ -82,9 +82,30 @@ 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 because as somehow the start/base location of
+		 * the Parent region of Stolen area which is PCI Bus 0000:00
+		 * is not coinciding with the start of Stolen area and is
+		 * conflicting with it. For ex. from the device memory map
+		 * info provided by '/proc/iomem', we have seen that somehow
+		 * a region of PCI Bus 0000:00 is being shown to start from
+		 * 0x7b000001, i.e. (7b000001-ffffffff : PCI Bus 0000:00).
+		 * And the stolen base is coming as 0x7b000000, thus there is a
+		 * conflict and stolen memory remains unused by the driver.
+		 * So to circumvent this issue we adjust the base of stolen
+		 * area by 1 when registering it with the kernel.
+		 */
+		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