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

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
...@@ -33,11 +33,20 @@ ...@@ -33,11 +33,20 @@
#include <drm/drm_fb_helper.h> #include <drm/drm_fb_helper.h>
#include <drm/drm_dp_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) ({ \ #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; \ int ret__ = 0; \
while (!(COND)) { \ while (!(COND)) { \
if (time_after(jiffies, timeout__)) { \ if (time_after(jiffies, timeout__)) { \
if (!(COND)) \
ret__ = -ETIMEDOUT; \ ret__ = -ETIMEDOUT; \
break; \ break; \
} \ } \
......
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