Messages in this thread | | | Date | Mon, 16 Aug 2010 13:56:34 +0200 | From | Lothar Waßmann <> | Subject | Re: [PATCH 1/3] dmaengine: add possibility for cyclic transfers |
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Hi,
Sascha Hauer writes: > Cyclic transfers are useful for audio where a single buffer divided > in periods has to be transfered endlessly until stopped. After being > prepared the transfer is started using the dma_async_descriptor->tx_submit > function. dma_async_descriptor->callback is called after each period. > The transfer is stopped using the DMA_TERMINATE_ALL callback. > While being used for cyclic transfers the channel cannot be used > for other transfer types. > > Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de> > Cc: Haavard Skinnemoen <haavard.skinnemoen@atmel.com> > --- > drivers/dma/dmaengine.c | 2 ++ > include/linux/dmaengine.h | 6 +++++- > 2 files changed, 7 insertions(+), 1 deletions(-) > > diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c > index 9d31d5e..e5e79ce 100644 > --- a/drivers/dma/dmaengine.c > +++ b/drivers/dma/dmaengine.c > @@ -692,6 +692,8 @@ int dma_async_device_register(struct dma_device *device) > !device->device_prep_dma_interrupt); > BUG_ON(dma_has_cap(DMA_SLAVE, device->cap_mask) && > !device->device_prep_slave_sg); > + BUG_ON(dma_has_cap(DMA_CYCLIC, device->cap_mask) && > + !device->device_prep_dma_cyclic); > BUG_ON(dma_has_cap(DMA_SLAVE, device->cap_mask) && > !device->device_control); > > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h > index c61d4ca..0df7864 100644 > --- a/include/linux/dmaengine.h > +++ b/include/linux/dmaengine.h > @@ -67,10 +67,11 @@ enum dma_transaction_type { > DMA_PRIVATE, > DMA_ASYNC_TX, > DMA_SLAVE, > + DMA_CYCLIC, > }; > > /* last transaction type for creation of the capabilities mask */ > -#define DMA_TX_TYPE_END (DMA_SLAVE + 1) > +#define DMA_TX_TYPE_END (DMA_CYCLIC + 1) > > > /** > @@ -478,6 +479,9 @@ struct dma_device { > struct dma_chan *chan, struct scatterlist *sgl, > unsigned int sg_len, enum dma_data_direction direction, > unsigned long flags); > + struct dma_async_tx_descriptor *(*device_prep_dma_cyclic)( > + struct dma_chan *chan, dma_addr_t buf_addr, size_t buf_len, > + size_t period_len, enum dma_data_direction direction); > int (*device_control)(struct dma_chan *chan, enum dma_ctrl_cmd cmd, > unsigned long arg); > > -- > 1.7.1 > Why not implement this feature using cyclic SG lists (created with sg_chain())? This would give you endless DMA transfers without any special DMA API extensions.
Lothar Waßmann -- ___________________________________________________________
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