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

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On 01/12/2017 11:09 AM, Tony Lindgren wrote:
> * Tony Lindgren <tony@xxxxxxxxxxx> [170109 10:35]:
>> Hi,
>>
>> * Alexandre Bailon <abailon@xxxxxxxxxxxx> [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@xxxxxxxxxxxx>
>>> ---
>>>  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?

This looks more close to what is provided in Documentation\power\runtime_pm.txt
(example at the end of the file),
but as per this document custom locking is required to access .active var.


> 
> 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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-- 
regards,
-grygorii
--
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