54 lines
2.1 KiB
Diff
54 lines
2.1 KiB
Diff
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From b75c5a66f0cc21a340beb462c4f051ee6cd53cb9 Mon Sep 17 00:00:00 2001
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From: Imre Deak <imre.deak@intel.com>
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Date: Wed, 1 May 2013 21:18:46 +0300
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Subject: [PATCH] drm/i915: fix DP AUX errors due to false timeouts when using
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wait_event_timeout
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Due to possible scheduling latencies wait_event_timeout doesn't
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guarantee a non-zero return value, even if the condition becomes true
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before the specified timeout expires. Thus we can incorrectly signal a
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timeout and abort a DP AUX transaction.
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If wait_event_timeout returns 0, it's guaranteed that at least the
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specified timeout (minus one jiffies, see below) had passed, so we can
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fix this by checking the condition explicitly in this case.
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Also the timeout that wait_event_timeout() is guaranteed to wait if the
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condition doesn't become true is one less jiffies than what is passed to
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it as a parameter. This is because the absolute expiration time in
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schedule_timeout() may be calculated at a moment close to the next
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scheduling tick, when jiffies is incremented. So make sure we pass always
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a jiffies value of 2 or greater. Here this makes a difference only for
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HZ=100.
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This fixes DP AUX errors I saw during booting on an ILK.
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This should ideally be fixed in wait_event_timeout(), but that can take
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a while. Until that's done use this fix as a band-aid.
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Signed-off-by: Imre Deak <imre.deak@intel.com>
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---
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drivers/gpu/drm/i915/intel_dp.c | 4 ++--
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1 file changed, 2 insertions(+), 2 deletions(-)
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diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
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index 8759fb1..7ce96c5 100644
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--- drivers/gpu/drm/i915/intel_dp.c
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+++ drivers/gpu/drm/i915/intel_dp.c
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@@ -303,10 +303,10 @@ intel_dp_aux_wait_done(struct intel_dp *intel_dp, bool has_aux_irq)
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#define C (((status = I915_READ_NOTRACE(ch_ctl)) & DP_AUX_CH_CTL_SEND_BUSY) == 0)
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if (has_aux_irq)
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done = wait_event_timeout(dev_priv->gmbus_wait_queue, C,
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- msecs_to_jiffies(10));
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+ msecs_to_jiffies(10) + 1);
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else
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done = wait_for_atomic(C, 10) == 0;
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- if (!done)
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+ if (!done && !(C))
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DRM_ERROR("dp aux hw did not signal timeout (has irq: %i)!\n",
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has_aux_irq);
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#undef C
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--
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1.7.10.4
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