[PATCH] DMAEngine: sirf: add DMA pause/resume support

[Barry Song]

2012/12/14, Russell King - ARM Linux <linux at arm.linux.org.uk>:
> On Fri, Dec 14, 2012 at 05:44:42PM +0800, Barry Song wrote:
>> diff --git a/drivers/dma/sirf-dma.c b/drivers/dma/sirf-dma.c
>> index 212f69f..ffe05bb 100644
>> --- a/drivers/dma/sirf-dma.c
>> +++ b/drivers/dma/sirf-dma.c
>> @@ -313,6 +313,38 @@ static int sirfsoc_dma_terminate_all(struct
>> sirfsoc_dma_chan *schan)
>>  	return 0;
>>  }
>>
>> +static int sirfsoc_dma_pause_chan(struct sirfsoc_dma_chan *schan)
>> +{
>> +	struct sirfsoc_dma *sdma = dma_chan_to_sirfsoc_dma(&schan->chan);
>> +	int cid = schan->chan.chan_id;
>> +
>> +	if (!sdma->is_marco)
>> +		writel_relaxed(readl_relaxed(sdma->base + SIRFSOC_DMA_CH_LOOP_CTRL)
>> +			& ~((1 << cid) | 1 << (cid + 16)),
>> +			sdma->base + SIRFSOC_DMA_CH_LOOP_CTRL);
>> +	else
>> +		writel_relaxed((1 << cid) | 1 << (cid + 16),
>> +			sdma->base + SIRFSOC_DMA_CH_LOOP_CTRL_CLR);
>
> You're doing a read-modify-write to what looks like a shared register.
> What makes this code safe in a preempt or SMP environment?

the new registers of SiRFmarco split into SET and CLR instead of old
read-modify-write. anyway, here i missed holding a spinlock for
SiRFprimaII.

-barry