[PATCH] drm/i915: fix wait_remaining_ms_from_jiffies

[Imre Deak <imre.deak@intel.com>]

schedule_timeout_uninterruptible() takes jiffies not ms.

Also we should check whether jiffies has overflowed since the timestamp
for event A was taken. This is highly unlikely on 64 bit, but on 32 bit
machines jiffies initially is -300*HZ. If the panel power is initially
off the first wait from edp_panel_vdd_on()->wait_panel_power_cycle()
will result in a call timestamp_jiffies of 0, so on 32 bit machines we
would wait ~300 sec + to_wait_ms. Fix this by checking if the initial
timestamp is not in the future.

Signed-off-by: Imre Deak <imre.deak@intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 3673ba1..6a80393 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2643,12 +2643,13 @@ timespec_to_jiffies_timeout(const struct timespec *value)
  * doesn't happen exactly after event A, you record the timestamp (jiffies) of
  * when event A happened, then just before event B you call this function and
  * pass the timestamp as the first argument, and X as the second argument.
+ * Note that the recorded timestamp (timestamp_jiffies) can't be in the future
+ * otherwise the function won't wait at all.
  */
 static inline void
 wait_remaining_ms_from_jiffies(unsigned long timestamp_jiffies, int to_wait_ms)
 {
-	unsigned long target_jiffies, tmp_jiffies;
-	unsigned int remaining_ms;
+	unsigned long target_jiffies, tmp_jiffies, remaining_jiffies;
 
 	/*
 	 * Don't re-read the value of "jiffies" every time since it may change
@@ -2658,12 +2659,12 @@ wait_remaining_ms_from_jiffies(unsigned long timestamp_jiffies, int to_wait_ms)
 	target_jiffies = timestamp_jiffies +
 			 msecs_to_jiffies_timeout(to_wait_ms);
 
-	if (time_after(target_jiffies, tmp_jiffies)) {
-		remaining_ms = jiffies_to_msecs((long)target_jiffies -
-						(long)tmp_jiffies);
-		while (remaining_ms)
-			remaining_ms =
-				schedule_timeout_uninterruptible(remaining_ms);
+	if (time_after(target_jiffies, tmp_jiffies) &&
+	    time_before_eq(timestamp_jiffies, tmp_jiffies)) {
+		remaining_jiffies = target_jiffies - tmp_jiffies;
+		while (remaining_jiffies)
+			remaining_jiffies =
+			    schedule_timeout_uninterruptible(remaining_jiffies);
 	}
 }
 
-- 
1.8.4