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Commit a6b0a141 authored by Chris Wilson's avatar Chris Wilson
Browse files

drm/i915/breadcrumbs: Tweak commentary 



Tvrtko spotted a stale reference to b->lock (now b->rb_lock) so review
the comments and try to improve them in passing.

Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170315222259.1469-1-chris@chris-wilson.co.uk


Reviewed-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
parent db93991b

drivers/gpu/drm/i915/intel_breadcrumbs.c

+17 −8
Original line number Diff line number Diff line
@@ -85,7 +85,7 @@ static void intel_breadcrumbs_hangcheck(unsigned long data) 
		return;

	}



	/* We keep the hangcheck time alive until we disarm the irq, even

	/* We keep the hangcheck timer alive until we disarm the irq, even

	 * if there are no waiters at present.

	 *

	 * If the waiter was currently running, assume it hasn't had a chance
@@ -110,12 +110,11 @@ static void intel_breadcrumbs_fake_irq(unsigned long data) 
	struct intel_engine_cs *engine = (struct intel_engine_cs *)data;

	struct intel_breadcrumbs *b = &engine->breadcrumbs;



	/*

	 * The timer persists in case we cannot enable interrupts,

	/* The timer persists in case we cannot enable interrupts,

	 * or if we have previously seen seqno/interrupt incoherency

	 * ("missed interrupt" syndrome). Here the worker will wake up

	 * every jiffie in order to kick the oldest waiter to do the

	 * coherent seqno check.

	 * ("missed interrupt" syndrome, better known as a "missed breadcrumb").

	 * Here the worker will wake up every jiffie in order to kick the

	 * oldest waiter to do the coherent seqno check.

	 */



	spin_lock_irq(&b->irq_lock);
@@ -290,7 +289,12 @@ static inline void __intel_breadcrumbs_finish(struct intel_breadcrumbs *b, 
	GEM_BUG_ON(b->irq_wait == wait);



	/* This request is completed, so remove it from the tree, mark it as

	 * complete, and *then* wake up the associated task.

	 * complete, and *then* wake up the associated task. N.B. when the

	 * task wakes up, it will find the empty rb_node, discern that it

	 * has already been removed from the tree and skip the serialisation

	 * of the b->rb_lock and b->irq_lock. This means that the destruction

	 * of the intel_wait is not serialised with the interrupt handler

	 * by the waiter - it must instead be serialised by the caller.

	 */

	rb_erase(&wait->node, &b->waiters);

	RB_CLEAR_NODE(&wait->node);
@@ -397,6 +401,11 @@ static bool __intel_engine_add_wait(struct intel_engine_cs *engine, 
	}



	if (completed) {

		/* Advance the bottom-half (b->irq_wait) before we wake up

		 * the waiters who may scribble over their intel_wait

		 * just as the interrupt handler is dereferencing it via

		 * b->irq_wait.

		 */

		if (!first) {

			struct rb_node *next = rb_next(completed);

			GEM_BUG_ON(next == &wait->node);
@@ -653,7 +662,7 @@ void intel_engine_enable_signaling(struct drm_i915_gem_request *request) 
	/* Note that we may be called from an interrupt handler on another

	 * device (e.g. nouveau signaling a fence completion causing us

	 * to submit a request, and so enable signaling). As such,

	 * we need to make sure that all other users of b->lock protect

	 * we need to make sure that all other users of b->rb_lock protect

	 * against interrupts, i.e. use spin_lock_irqsave.

	 */