drm/vblank: Fix vblank timestamp debugs

We're currently calling ktime_to_timespec64() on stack garbage
hence the debug output for vblank timestamps also contains garbage.
Let's assing something to the ktime_t first before we go converting
it to a timespec.

While at it micro-optimize the ktime_to_timespec64() calls away
when vblank debugging isn't enabled.

Fixes: 67680d3c0464 ("drm: vblank: use ktime_t instead of timeval")
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Keith Packard <keithp@keithp.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: Dave Airlie <airlied@redhat.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171113150210.11311-1-ville.syrjala@linux.intel.com
Acked-by: Arnd Bergmann <arnd@arndb.de>

1 files changed, 7 insertions, 5 deletions

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 09c1c4ff93ca..2c68909637b5 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -664,14 +664,16 @@ bool drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev,
         delta_ns = div_s64(1000000LL * (vpos * mode->crtc_htotal + hpos),
                            mode->crtc_clock);
 
-        /* save this only for debugging purposes */
-        ts_etime = ktime_to_timespec64(etime);
-        ts_vblank_time = ktime_to_timespec64(*vblank_time);
         /* Subtract time delta from raw timestamp to get final
          * vblank_time timestamp for end of vblank.
          */
-        etime = ktime_sub_ns(etime, delta_ns);
-        *vblank_time = etime;
+        *vblank_time = ktime_sub_ns(etime, delta_ns);
+
+        if ((drm_debug & DRM_UT_VBL) == 0)
+                return true;
+
+        ts_etime = ktime_to_timespec64(etime);
+        ts_vblank_time = ktime_to_timespec64(*vblank_time);
 
         DRM_DEBUG_VBL("crtc %u : v p(%d,%d)@ %lld.%06ld -> %lld.%06ld [e %d us, %d rep]\n",
                       pipe, hpos, vpos,