[Intel-gfx] [PATCH] drm/i915: overlay on gen2 can't address above 1G

[Daniel Vetter]

So set the coherent dma mask accordingly. This dma mask is only used
for physical objects, so it won't really matter allocation-wise.

Now this never really surfaced because sane 32bit kernels only have 1G
of lowmem. But some eager testers (distros?) still carry around the patch
to adjust lowmem via a kconfig option. And the kernel seems to favour
high allocations on boot-up, hence the overlay blowing up reliably.

Because the patch is tiny and nicely shows how broken gen2 is it's imho
worth to merge despite the fact that mucking around with the lowmem/
highmem division is (no longer) supported.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=28318
Cc: stable at kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/i915/i915_dma.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index a2d3509..d609747 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -2075,6 +2075,10 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
 		goto free_priv;
 	}
 
+	/* overlay on gen2 is broken and can't address above 1G */
+	if (IS_GEN2(dev))
+		dma_set_coherent_mask(&dev->pdev->dev, DMA_BIT_MASK(30));
+
 	dev_priv->regs = ioremap(base, size);
 	if (!dev_priv->regs) {
 		DRM_ERROR("failed to map registers\n");
-- 
1.7.1