linux-kernel - Re: [PATCH 2/2] dma:of: Use a mutex to protect the of_dma

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Date:	Sat, 20 Apr 2013 09:28:19 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Jon Hunter <jon-hunter@...com>
CC:	Vinod Koul <vinod.koul@...el.com>, Arnd Bergmann <arnd@...db.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] dma:of: Use a mutex to protect the of_dma_list

On 04/20/2013 12:45 AM, Jon Hunter wrote:
[...]
>> @@ -219,15 +183,15 @@ struct dma_chan *of_dma_request_slave_channel(struct device_node *np,
>>  		if (of_dma_match_channel(np, name, i, &dma_spec))
>>  			continue;
>>  
>> -		ofdma = of_dma_get_controller(&dma_spec);
>> +		mutex_lock(&of_dma_lock);
>> +		ofdma = of_dma_find_controller(&dma_spec);
>>  
>> -		if (ofdma) {
>> +		if (ofdma)
>>  			chan = ofdma->of_dma_xlate(&dma_spec, ofdma);
> 
> I think that there is a problem here. For controllers using the
> of_dma_simple_xlate(), this will call dma_request_channel() which also
> uses a mutex.

That would only be a problem if it'd use the same mutex. Holding two mutexes at
the same time is not a problem per se.

- Lars
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