linux-kernel - Re: [PATCH 1/7 v2] dmaengine: add a simple dma library

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Message-id: <4F28A7C7.8060500@renesas.com>
Date:	Wed, 01 Feb 2012 11:47:35 +0900
From:	"Shimoda, Yoshihiro" <yoshihiro.shimoda.uh@...esas.com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	linux-kernel@...r.kernel.org, linux-sh@...r.kernel.org,
	Vinod Koul <vinod.koul@...el.com>,
	Magnus Damm <magnus.damm@...il.com>, linux-mmc@...r.kernel.org,
	alsa-devel@...a-project.org, linux-serial@...r.kernel.org,
	Paul Mundt <lethal@...ux-sh.org>
Subject: Re: [PATCH 1/7 v2] dmaengine: add a simple dma library

Hi Guennadi-san,

2012/02/01 9:52, Guennadi Liakhovetski wrote:
> Hi Shimoda-san
> 
> On Tue, 31 Jan 2012, Shimoda, Yoshihiro wrote:
[ snip ]
>> I investigaed the issue. I found out the renesas_usbhs driver may
>> call tx_submit() in the callback()
> 
> Well, actually, this is not something, that shdma officially supports ATM. 
> Originally it was prohibited by the API, but later a correction has been 
> added to Documentation/dmaengine.txt, explicitly allowing this. So, good, 
> if this works for you, but watch out for possible issues.
>
>> of the dma-simple finally.
>> In this case, the value of power_up in the simple_tx_submit is 0,
>> the start_xfer() is not called. And then, even if the ld_queue is
>> not empty, the DMA doesn't start.
> 
> This is correct. As soon as all the transfers, currently queued in the 
> shdma driver, has been processed and completed, to restart DMA you need to 
> call dma_async_issue_pending().
> 
>> So, if I add codes like the following in the dma-simple.c,
>> the renesas_usbhs driver can work correctly without the driver changes.
>> If you think the code is good, would you merge it to your code?
>> ======= chan_irqt() =======
>> 	simple_chan_ld_cleanup(schan, false);
>>
>> +	spin_lock_irq(&schan->chan_lock);
>> +	/* Next desc */
>> +	simple_chan_xfer_ld_queue(schan);
>> +	spin_unlock_irq(&schan->chan_lock);
>>
>> 	return IRQ_HANDLED;
>> ==============
> 
> Therefore, no, this shouldn't be needed.

Thank you very much for your comment.
I understood it. I will investigate the renesas_usbhs driver more.

Best regards,
Yoshihiro Shimoda

> Thanks
> Guennadi
> 
>>
>> Best regards,
>> Yoshihiro Shimoda
>>
>>> Thanks
>>> Guennadi
>>>
>>>> For reference, if I changed the threaded IRQ to tasklet,
>>>> the 2 environment worked correctly:
>>>> ==============
>>>> diff --git a/drivers/dma/dma-simple.c b/drivers/dma/dma-simple.c
>>>> index 49d8f7d..65a5170 100644
>>>> --- a/drivers/dma/dma-simple.c
>>>> +++ b/drivers/dma/dma-simple.c
>>>> @@ -715,16 +715,18 @@ static irqreturn_t chan_irq(int irq, void *dev)
>>>>
>>>>  	spin_lock(&schan->chan_lock);
>>>>
>>>> -	ret = ops->chan_irq(schan, irq) ? IRQ_WAKE_THREAD : IRQ_NONE;
>>>> +	ret = ops->chan_irq(schan, irq) ? IRQ_HANDLED : IRQ_NONE;
>>>> +	if (ret == IRQ_HANDLED)
>>>> +		tasklet_schedule(&schan->tasklet);
>>>>
>>>>  	spin_unlock(&schan->chan_lock);
>>>>
>>>>  	return ret;
>>>>  }
>>>>
>>>> -static irqreturn_t chan_irqt(int irq, void *dev)
>>>> +static void chan_irqt(unsigned long dev)
>>>>  {
>>>> -	struct dma_simple_chan *schan = dev;
>>>> +	struct dma_simple_chan *schan = (struct dma_simple_chan *)dev;
>>>>  	const struct dma_simple_ops *ops =
>>>>  		to_simple_dev(schan->dma_chan.device)->ops;
>>>>  	struct dma_simple_desc *sdesc;
>>>> @@ -744,15 +746,13 @@ static irqreturn_t chan_irqt(int irq, void *dev)
>>>>  	spin_unlock_irq(&schan->chan_lock);
>>>>
>>>>  	simple_chan_ld_cleanup(schan, false);
>>>> -
>>>> -	return IRQ_HANDLED;
>>>>  }
>>>>
>>>>  int dma_simple_request_irq(struct dma_simple_chan *schan, int irq,
>>>>  			   unsigned long flags, const char *name)
>>>>  {
>>>> -	int ret = request_threaded_irq(irq, chan_irq, chan_irqt,
>>>> -				       flags, name, schan);
>>>> +	int ret = request_irq(irq, chan_irq, flags, name, schan);
>>>> +	tasklet_init(&schan->tasklet, chan_irqt, (unsigned long)schan);
>>>>
>>>>  	schan->irq = ret < 0 ? ret : irq;
>>>>
>>>> diff --git a/include/linux/dma-simple.h b/include/linux/dma-simple.h
>>>> index 5336674..beb1489 100644
>>>> --- a/include/linux/dma-simple.h
>>>> +++ b/include/linux/dma-simple.h
>>>> @@ -68,6 +68,7 @@ struct dma_simple_chan {
>>>>  	int id;				/* Raw id of this channel */
>>>>  	int irq;			/* Channel IRQ */
>>>>  	enum dma_simple_pm_state pm_state;
>>>> +	struct tasklet_struct tasklet;
>>>>  };
>>>>
>>>>  /**
>>>> ==============
>>>>
>>>> Best regards,
>>>> Yoshihiro Shimoda
>>>>
>>>
>>> ---
>>> Guennadi Liakhovetski, Ph.D.
>>> Freelance Open-Source Software Developer
>>> http://www.open-technology.de/
>>>
>>
>>
>> -- 
>> Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
>> EC No.
>>
> 
> ---
> Guennadi Liakhovetski, Ph.D.
> Freelance Open-Source Software Developer
> http://www.open-technology.de/
> 


-- 
Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
EC No.
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