Re: [PATCH v2 1/2] dmaengine: cppi41: Fix list not empty warning on runtime suspend

[Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org>]

* Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org> [170109 10:35]:
> Hi,
> 
> * Alexandre Bailon <abailon-rdvid1DuHRBWk0Htik3J/w@public.gmane.org> [170109 09:04]:
> > Sometime, a transfer may not be queued due to a race between runtime pm
> > and cppi41_dma_issue_pending().
> > Sometime, cppi41_runtime_resume() may be interrupted right before to
> > update device PM state to RESUMED.
> > When it happens, if a new dma transfer is issued, because the device is not
> > in active state, the descriptor will be added to the pendding list.
> > But because the descriptors in the pendding list are only queued to cppi41
> > on runtime resume, the descriptor will not be queued.
> > On runtime suspend, the list is not empty, which is causing a warning.
> > Queue the descriptor if the device is active or resuming.
> > 
> > Signed-off-by: Alexandre Bailon <abailon-rdvid1DuHRBWk0Htik3J/w@public.gmane.org>
> > ---
> >  drivers/dma/cppi41.c | 18 +++++++++++++++++-
> >  1 file changed, 17 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/dma/cppi41.c b/drivers/dma/cppi41.c
> > index d5ba43a..025fee4 100644
> > --- a/drivers/dma/cppi41.c
> > +++ b/drivers/dma/cppi41.c
> > @@ -471,6 +471,8 @@ static void cppi41_dma_issue_pending(struct dma_chan *chan)
> >  {
> >  	struct cppi41_channel *c = to_cpp41_chan(chan);
> >  	struct cppi41_dd *cdd = c->cdd;
> > +	unsigned long flags;
> > +	bool active;
> >  	int error;
> >  
> >  	error = pm_runtime_get(cdd->ddev.dev);
> > @@ -482,7 +484,21 @@ static void cppi41_dma_issue_pending(struct dma_chan *chan)
> >  		return;
> >  	}
> >  
> > -	if (likely(pm_runtime_active(cdd->ddev.dev)))
> > +	active = pm_runtime_active(cdd->ddev.dev);
> > +	if (!active) {
> > +		/*
> > +		 * Runtime resume may be interrupted before runtime_status
> > +		 * has been updated. Test if device has resumed.
> > +		 */
> > +		if (error == -EINPROGRESS) {
> > +			spin_lock_irqsave(&cdd->lock, flags);
> > +			if (list_empty(&cdd->pending))
> > +				active = true;
> > +			spin_unlock_irqrestore(&cdd->lock, flags);
> > +		}
> > +	}
> > +
> > +	if (likely(active))
> >  		push_desc_queue(c);
> >  	else
> >  		pending_desc(c);
> 
> What guarantees that the PM runtime state is really active few lines later?
> 
> A safer approach might be to check the queue for new entries by in
> cppi41_runtime_resume() using "while (!list_empty())" instead of
> list_for_each_entry(). That releases the spinlock between each entry
> and rechecks the list.
> 
> And instead of doing WARN_ON(!list_empty(&cdd->pending)) it seems we
> should run the queue also on cppi41_runtime_suspend()?

Hmm so I started seeing these issues too with Linux next just plugging
in USB cable on bbb while configured as a USB peripheral :)

Below is what seems to fix issues for me, not seeing any more warnings
either.

Care to give it a try with your USB headset?

Regards,

Tony

8< --------------------------
diff --git a/drivers/dma/cppi41.c b/drivers/dma/cppi41.c
--- a/drivers/dma/cppi41.c
+++ b/drivers/dma/cppi41.c
@@ -153,6 +153,8 @@ struct cppi41_dd {
 
 	/* context for suspend/resume */
 	unsigned int dma_tdfdq;
+
+	bool active;
 };
 
 #define FIST_COMPLETION_QUEUE	93
@@ -320,7 +322,8 @@ static irqreturn_t cppi41_irq(int irq, void *data)
 			int error;
 
 			error = pm_runtime_get(cdd->ddev.dev);
-			if (error < 0)
+			if (((error != -EINPROGRESS) && error < 0) ||
+			    !cdd->active)
 				dev_err(cdd->ddev.dev, "%s pm runtime get: %i\n",
 					__func__, error);
 
@@ -482,7 +485,7 @@ static void cppi41_dma_issue_pending(struct dma_chan *chan)
 		return;
 	}
 
-	if (likely(pm_runtime_active(cdd->ddev.dev)))
+	if (likely(cdd->active))
 		push_desc_queue(c);
 	else
 		pending_desc(c);
@@ -1151,6 +1154,7 @@ static int __maybe_unused cppi41_runtime_suspend(struct device *dev)
 {
 	struct cppi41_dd *cdd = dev_get_drvdata(dev);
 
+	cdd->active = false;
 	WARN_ON(!list_empty(&cdd->pending));
 
 	return 0;
@@ -1159,13 +1163,20 @@ static int __maybe_unused cppi41_runtime_suspend(struct device *dev)
 static int __maybe_unused cppi41_runtime_resume(struct device *dev)
 {
 	struct cppi41_dd *cdd = dev_get_drvdata(dev);
-	struct cppi41_channel *c, *_c;
+	struct cppi41_channel *c;
 	unsigned long flags;
 
+	cdd->active = true;
+
 	spin_lock_irqsave(&cdd->lock, flags);
-	list_for_each_entry_safe(c, _c, &cdd->pending, node) {
-		push_desc_queue(c);
+	while (!list_empty(&cdd->pending)) {
+		c = list_first_entry(&cdd->pending,
+				     struct cppi41_channel,
+				     node);
 		list_del(&c->node);
+		spin_unlock_irqrestore(&cdd->lock, flags);
+		push_desc_queue(c);
+		spin_lock_irqsave(&cdd->lock, flags);
 	}
 	spin_unlock_irqrestore(&cdd->lock, flags);
 
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