From 352a3a11e3bb8cb49d995d478a56593a64c5a96a Mon Sep 17 00:00:00 2001 From: Imre Deak Date: Thu, 2 May 2013 12:00:03 +0300 Subject: [PATCH 1/8] drm/i915: fix DP AUX errors due to false timeouts when using wait_event_timeout Due to possible scheduling latencies wait_event_timeout doesn't guarantee a non-zero return value, even if the condition becomes true before the specified timeout expires. Thus we can incorrectly signal a timeout and abort a DP AUX transaction. If wait_event_timeout returns 0, it's guaranteed that at least the specified timeout (minus one jiffies, see below) had passed, so we can fix this by checking the condition explicitly in this case. Also the timeout that wait_event_timeout() is guaranteed to wait if the condition doesn't become true is one less jiffies than what is passed to it as a parameter. This is because the absolute expiration time in schedule_timeout() may be calculated at a moment close to the next scheduling tick, when jiffies is incremented. So make sure we pass always a jiffies value of 2 or greater. Here this makes a difference only for HZ=100. This fixes DP AUX errors I saw during booting on an ILK. This should ideally be fixed in wait_event_timeout(), but that can take a while. Until that's done use this fix as a band-aid. Signed-off-by: Imre Deak --- drivers/gpu/drm/i915/intel_dp.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c index 65d28cb..d5a3717 100644 --- a/drivers/gpu/drm/i915/intel_dp.c +++ b/drivers/gpu/drm/i915/intel_dp.c @@ -303,10 +303,10 @@ intel_dp_aux_wait_done(struct intel_dp *intel_dp, bool has_aux_irq) #define C (((status = I915_READ_NOTRACE(ch_ctl)) & DP_AUX_CH_CTL_SEND_BUSY) == 0) if (has_aux_irq) done = wait_event_timeout(dev_priv->gmbus_wait_queue, C, - msecs_to_jiffies(10)); + msecs_to_jiffies(10) + 1); else done = wait_for_atomic(C, 10) == 0; - if (!done) + if (!done && !(C)) DRM_ERROR("dp aux hw did not signal timeout (has irq: %i)!\n", has_aux_irq); #undef C -- 1.7.10.4