linux-kernel - Re: [PATCH 1/2] dma: cppi41: start tear down only if channel is busy

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Date:	Fri, 28 Feb 2014 11:23:41 +0530
From:	George Cherian <george.cherian@...com>
To:	"Shevchenko, Andriy" <andriy.shevchenko@...el.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"balbi@...com" <balbi@...com>,
	"Williams, Dan J" <dan.j.williams@...el.com>,
	"Koul, Vinod" <vinod.koul@...el.com>,
	"msmucr@...il.com" <msmucr@...il.com>
Subject: Re: [PATCH 1/2] dma: cppi41: start tear down only if channel is busy

On 2/27/2014 2:17 PM, Shevchenko, Andriy wrote:
> On Thu, 2014-02-27 at 10:44 +0530, George Cherian wrote:
>> Start the channel tear down only if the channel is busy, else just
>> bail out. In some cases its seen that by the time the tear down is
>> initiated the cppi completes the DMA, especially in ISOCH transfers.
>>
>> Signed-off-by: George Cherian <george.cherian@...com>
>> ---
>>   drivers/dma/cppi41.c | 7 +++++--
>>   1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/dma/cppi41.c b/drivers/dma/cppi41.c
>> index c18aebf..d028f36 100644
>> --- a/drivers/dma/cppi41.c
>> +++ b/drivers/dma/cppi41.c
>> @@ -620,12 +620,15 @@ static int cppi41_stop_chan(struct dma_chan *chan)
>>   	u32 desc_phys;
>>   	int ret;
>>   
>> +	desc_phys = lower_32_bits(c->desc_phys);
>> +	desc_num = (desc_phys - cdd->descs_phys) / sizeof(struct cppi41_desc);
>> +	if (!cdd->chan_busy[desc_num])
>> +		return 0;
>> +
>>   	ret = cppi41_tear_down_chan(c);
>>   	if (ret)
>>   		return ret;
>>   
>> -	desc_phys = lower_32_bits(c->desc_phys);
>> -	desc_num = (desc_phys - cdd->descs_phys) / sizeof(struct cppi41_desc);
>>   	WARN_ON(!cdd->chan_busy[desc_num]);
> Do you still need this WARN_ON?

Yes in some cases wherein the channel is busy and tear down didn't 
happen successfully.
>
>>   	cdd->chan_busy[desc_num] = NULL;
>>   
>


-- 
-George

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