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Commit 1d5bfac9 authored by Daniel Vetter's avatar Daniel Vetter
Browse files

drm/i915: fix up _wait_for macro 



As Thomas Gleixner spotted, it's rather horrible racy:
- We can miss almost a full tick, so need to compensate by 1 jiffy.
- We need to re-check the condition when having timed-out, since a
  the last check could have been before the timeout expired. E.g. when
  we've been preempted or a long irq happened.

Cc: Thomas Gleixner <tglx@linutronix.de>
Reported-by: default avatarJack Winter <jbh@alchemy.lu>
Cc: Jack Winter <jbh@alchemy.lu>
Reviewed-by: default avatarVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
parent 6effa33b

drivers/gpu/drm/i915/intel_drv.h

+11 −2
Original line number Diff line number Diff line
@@ -33,11 +33,20 @@ 
#include <drm/drm_fb_helper.h>

#include <drm/drm_dp_helper.h>



/**

 * _wait_for - magic (register) wait macro

 *

 * Does the right thing for modeset paths when run under kdgb or similar atomic

 * contexts. Note that it's important that we check the condition again after

 * having timed out, since the timeout could be due to preemption or similar and

 * we've never had a chance to check the condition before the timeout.

 */

#define _wait_for(COND, MS, W) ({ \

	unsigned long timeout__ = jiffies + msecs_to_jiffies(MS);	\

	unsigned long timeout__ = jiffies + msecs_to_jiffies(MS) + 1;	\

	int ret__ = 0;							\

	while (!(COND)) {						\

		if (time_after(jiffies, timeout__)) {			\

			if (!(COND))					\

				ret__ = -ETIMEDOUT;			\

			break;						\

		}							\