On Thu, May 14, 2009 at 09:27:17AM -0700, Dan Williams wrote: > On Thu, 2009-05-14 at 09:13 -0700, Ira Snyder wrote: > > Hello all. > > > > I'm working on a driver for a custom board (based heavily on the > > MPC8349EMDS board) to dump data out of onboard FPGA's. I need to use the > > onboard DMA controller for this, mostly due to data transfer rate and > > timing requirements. > > > > Of course, I'd like to "play nice" with the existing Linux > > infrastructure in my driver, even though I have no plans to submit the > > driver upstream (since it is only useful for our custom board). > > > > I have been using the DMAEngine API to interact with the DMA controller, > > and it works without any problems. However it seems that it is missing > > one of the major features that is supported by almost all DMA > > controllers: scatter/gather support. > > > > What I'd really like to do is give the controller a scatterlist and list > > of hardware addresses, and have it set up the transfer. The Freescale > > hardware can handle this, and I could program it by hand to do so, but I > > don't want to invent my own DMA API. > > > > I'm aware that the DMAEngine API was designed to offload memcpy, and > > pretty much nothing else. Is there any chance that such a change would > > be accepted into the mainline kernel? Any opinions on what such an API > > should look like? > > > > Have you taken a look at the 'slave' interface implemented by dw_dmac > and other drivers? It has the following interface: > > struct dma_async_tx_descriptor *(*device_prep_slave_sg)( > struct dma_chan *chan, struct scatterlist *sgl, > unsigned int sg_len, enum dma_data_direction direction, > unsigned long flags); > > Haavard uses this interface to do sgl transfers on behalf of the > atmel-mci driver (drivers/mmc/host/atmel-mci.c). >
I had started looking at it, though the Freescale device does not implement DMA_SLAVE support. I was a bit discouraged by the changelog for commit dc0ee643, which says that the interface is for "DMA with hardware handshaking", which I do not have. There is not anything special about accessing the FPGA's, they appear in the processor's memory map and can be read from/written to just like RAM. I'll try studying the dw_dmac implementation and atmel-mci example. Thanks for the response, Ira _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
