agp/intel: Flush the chipset write buffers when changing GTT base

Flush the chipset write buffers before and after adjusting the GTT base
register, just in case. We only modify this value upon initialisation
(boot and resume) so there should be no outstanding writes, however
there are always those persistent PGTBL_ER that keep getting reported
upon resume.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 9 insertions, 0 deletions

diff --git a/drivers/char/agp/intel-gtt.c b/drivers/char/agp/intel-gtt.c
index 356f73e0d17e..da8161806f39 100644
--- a/drivers/char/agp/intel-gtt.c
+++ b/drivers/char/agp/intel-gtt.c
@@ -814,6 +814,12 @@ static bool intel_enable_gtt(void)
                 }
         }
 
+        /* On the resume path we may be adjusting the PGTBL value, so
+         * be paranoid and flush all chipset write buffers...
+         */
+        if (INTEL_GTT_GEN >= 3)
+                writel(0, intel_private.registers+GFX_FLSH_CNTL);
+
         reg = intel_private.registers+I810_PGETBL_CTL;
         writel(intel_private.PGETBL_save, reg);
         if (HAS_PGTBL_EN && (readl(reg) & I810_PGETBL_ENABLED) == 0) {
@@ -823,6 +829,9 @@ static bool intel_enable_gtt(void)
                 return false;
         }
 
+        if (INTEL_GTT_GEN >= 3)
+                writel(0, intel_private.registers+GFX_FLSH_CNTL);
+
         return true;
 }