Re: [PATCHv4] DMAEngine: Define interleaved transfer request api
From: Russell King
Date: Mon Oct 03 2011 - 12:14:16 EST
On Mon, Oct 03, 2011 at 11:54:23AM +0530, Jassi Brar wrote:
> On 2 October 2011 06:03, Barry Song <21cnbao@xxxxxxxxx> wrote:
> > 2011/10/2 Jassi Brar <jaswinder.singh@xxxxxxxxxx>
> >> > For example, it can't use
> >> > MEM_TO_MEM to map, it still need to know whether the memory is source
> >> > or dest.
> >> MEM_TO_MEM means "From Memory Source To Memory Destination"
> >> Map Src buffer with DMA_TO_DEVICE and Dst buffer with DMA_FROM_DEVICE
> >> MEM_TO_DEV means "From Memory Source To FIFO Destination"
> >> Map Src buffer with DMA_TO_DEVICE.
> >> DEV_TO_MEM means "From FIFO Source To Memory Destination"
> >> Map Dst buffer with DMA_FROM_DEVICE
> >> DEV_TO_DEV means "From FIFO Source To FIFO Destination"
> >> What else would you want to know ?
> > that is the problem. for example, drivers can't use MEM_TO_MEM as a
> > flag to do dma mapping. so xfer_direction can't cover all that
> > dma_data_direction can do. that's why you need both
> > dma_data_direction and xfer_direction with some similar flags in them.
> The client drivers map the src/dst buffers and the dmac driver unmaps
> them by default(!). For which, the dmac driver doesn't look at anything
> other than
> bits of 'enum dma_ctrl_flags'.
> For this unmap'ing purpose, the usage of dma_data_direction is already
> internal to the dmac driver.
No. Slave DMA engine drivers do *not* (and if they do, they should *not*)
honour the unmapping of submitted buffers.
The unmapping of these buffers by the DMA engine driver is intended to be
done for the async_tx API and not slave DMA.
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
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