After changing the timing between GTT updates and execution on the GPU,
we started seeing sporadic failures on Ironlake. These were narrowed
down to being an insufficiently strong enough barrier/delay after
updating the GTT and scheduling execution on the GPU. By forcing the
uncached read, and adding the missing barrier for the singular
insert_page (relocation paths), the sporadic failures go away.
Fixes: 983d308cb8f6 ("agp/intel: Serialise after GTT updates")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v4.0+
---
drivers/char/agp/intel-gtt.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/char/agp/intel-gtt.c b/drivers/char/agp/intel-gtt.c
index 66a62d17a3f5..3d42fc4290bc 100644
--- a/drivers/char/agp/intel-gtt.c
+++ b/drivers/char/agp/intel-gtt.c
@@ -846,6 +846,7 @@ void intel_gtt_insert_page(dma_addr_t addr,
unsigned int flags)
{
intel_private.driver->write_entry(addr, pg, flags);
+ readl(intel_private.gtt + pg);
if (intel_private.driver->chipset_flush)
intel_private.driver->chipset_flush();
}
@@ -871,7 +872,7 @@ void intel_gtt_insert_sg_entries(struct sg_table *st,
j++;
}
}
- wmb();
+ readl(intel_private.gtt + j - 1);
if (intel_private.driver->chipset_flush)
intel_private.driver->chipset_flush();
}
@@ -1105,6 +1106,7 @@ static void i9xx_cleanup(void)
static void i9xx_chipset_flush(void)
{
+ wmb();
if (intel_private.i9xx_flush_page)
writel(1, intel_private.i9xx_flush_page);
}
--
2.20.1
