linux-kernel - Re: [PATCH V2 2/2] dmaengine: tegra-adma: Add support for Tegra210 ADMA

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Date:	Tue, 6 Oct 2015 10:45:01 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Laxman Dewangan <ldewangan@...dia.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	"Kumar Gala" <galak@...eaurora.org>, <dmaengine@...r.kernel.org>,
	<linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 2/2] dmaengine: tegra-adma: Add support for Tegra210
 ADMA


On 06/10/15 10:32, Arnd Bergmann wrote:
> On Monday 05 October 2015 13:10:07 Jon Hunter wrote:
>> Add support for the Tegra210 Audio DMA controller that is used for
>> transferring data between system memory and the Audio sub-system.
>> The driver only supports cyclic transfers because this is being solely
>> used for audio.
>>
>> This driver is based upon the work by Dara Ramesh <dramesh@...dia.com>.
>>
>> Signed-off-by: Jon Hunter <jonathanh@...dia.com>
> 
> This version looks much better!
> 
> Just one small comment:
> 
>> +	slave_req = dma_spec->args[0];
>> +	slave_dir = dma_spec->args[1];
>> +
>> +	if (slave_req == 0)
>> +		return NULL;
>> +
>> +	switch (slave_dir) {
>> +	case ADMA_AHUB_TO_MEM:
>> +		if (slave_req > tdma->rx_requests)
>> +			return NULL;
>> +
>> +		if (tdma->rx_requests_reserved & BIT(slave_req))
>> +			return NULL;
>> +
>> +		tdma->rx_requests_reserved |= BIT(slave_req);
>> +		break;
> 
> The rx_requests_reserved logic looks racy, if you have more than
> one concurrent request or release. Better use atomic_test_and_set()
> here and turn the variable into an atomic_t.

Ah yes, will update.

Thanks
Jon
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