drm/i915: Use ktime on wait_for

We use jiffies to determine when wait expires. However
Imre did find out that jiffies can and will do a >1
increments on certain situations [1]. When this happens
in a wait_for loop, we return timeout errorneously
much earlier than what the real wallclock would say.

We can't afford our waits to timeout prematurely.
Discard jiffies and change to ktime to detect timeouts.

v2: added bugzilla entry (Imre), added stable (Chris)

Reported-by: Imre Deak <imre.deak@intel.com>
References: https://lkml.org/lkml/2018/4/18/798 [1]
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105771
Cc: Imre Deak <imre.deak@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180423113754.28424-1-mika.kuoppala@linux.intel.com

diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 44ed248f1fe9d87484ef1e543dea1680f4226f61..33ff2638c92bbf92641b2d19f7ed5311f5a182c0 100644 (file)
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -49,12 +49,12 @@
  * check the condition before the timeout.
  */
 #define __wait_for(OP, COND, US, Wmin, Wmax) ({ \
-       unsigned long timeout__ = jiffies + usecs_to_jiffies(US) + 1;   \
+       const ktime_t end__ = ktime_add_ns(ktime_get_raw(), 1000ll * (US)); \
        long wait__ = (Wmin); /* recommended min for usleep is 10 us */ \
        int ret__;                                                      \
        might_sleep();                                                  \
        for (;;) {                                                      \
-               bool expired__ = time_after(jiffies, timeout__);        \
+               const bool expired__ = ktime_after(ktime_get_raw(), end__); \
                OP;                                                     \
                if (COND) {                                             \
                        ret__ = 0;                                      \