drm/i915: Squelch any ktime/jiffie rounding errors for wait-ioctl

We wait upon jiffies, but report the time elapsed using a
high-resolution timer. This discrepancy can lead to us timing out the
wait prior to us reporting the elapsed time as complete.

This restores the squelching lost in commit e95433c73a11 ("drm/i915:
Rearrange i915_wait_request() accounting with callers").

Fixes: e95433c73a11 ("drm/i915: Rearrange i915_wait_request() accounting with callers")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.william.auld@gmail.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: <drm-intel-fixes@lists.freedesktop.org> # v4.10-rc1+
Cc: stable@vger.kernel.org
Link: http://patchwork.freedesktop.org/patch/msgid/20170216125441.30923-1-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
(cherry picked from commit c1d2061b28c2aa25ec39b60d9c248e6beebd7315)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 6908123162d1..c45af09555dc 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3029,6 +3029,16 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
                 args->timeout_ns -= ktime_to_ns(ktime_sub(ktime_get(), start));
                 if (args->timeout_ns < 0)
                         args->timeout_ns = 0;
+
+                /*
+                 * Apparently ktime isn't accurate enough and occasionally has a
+                 * bit of mismatch in the jiffies<->nsecs<->ktime loop. So patch
+                 * things up to make the test happy. We allow up to 1 jiffy.
+                 *
+                 * This is a regression from the timespec->ktime conversion.
+                 */
+                if (ret == -ETIME && !nsecs_to_jiffies(args->timeout_ns))
+                        args->timeout_ns = 0;
         }
 
         i915_gem_object_put(obj);