Attachment 79021 Details for Bug 64270 – fix for dpaux false timeouts

fix for dpaux false timeouts

0001-drm-i915-fix-DP-AUX-errors-due-to-false-timeouts-whe.patch (text/plain), 2.10 KB, created by Imre Deak on 2013-05-08 10:38:23 UTC

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Creator: Imre Deak

Created: 2013-05-08 10:38:23 UTC

Size: 2.10 KB

patch

obsolete

>From 352a3a11e3bb8cb49d995d478a56593a64c5a96a Mon Sep 17 00:00:00 2001
>From: Imre Deak <imre.deak@intel.com>
>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 <imre.deak@intel.com>
>---
> 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
>

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Attachments on bug 64270: 78931 | 78979 | 79019 | 79021

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