On Thu, Mar 28, 2013 at 12:03:25AM +0100, Daniel Vetter wrote:
> As Thomas Gleixner spotted, it's rather horrible racy:
> - We can miss almost a full tick, so need to compensate by 1 jiffy.
I have a feeling this is a rather common pattern, so I wonder
if [mu]secs_to_jiffies() should do the +1 already for everyone.
Or maybe there should be some other macros for specifying
timeouts that would do the +1.
> - 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 at linutronix.de>
> Reported-by: Jack Winter <jbh at alchemy.lu>
> Cc: Jack Winter <jbh at alchemy.lu>
> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Reviewed-by: Ville Syrj?l? <ville.syrjala at linux.intel.com>
> ---
> drivers/gpu/drm/i915/intel_drv.h | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index c8c1979..9dcae4e 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -33,12 +33,21 @@
> #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__)) { \
> - ret__ = -ETIMEDOUT; \
> + if (!(COND)) \
> + ret__ = -ETIMEDOUT; \
> break; \
> } \
> if (W && drm_can_sleep()) { \
> --
> 1.7.11.7
>
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> Intel-gfx at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
--
Ville Syrj?l?
Intel OTC
