On 28-04-20, 18:10, Alan Mikhak wrote: > From: Alan Mikhak <alan.mikhak@xxxxxxxxxx> > > Modify dw_edma_device_transfer() to also support the semantics of dma > device transfer for additional use cases involving pcitest utility as a > local initiator. > > For its original use case, dw-edma supported the semantics of dma device > transfer from the perspective of a remote initiator who is located across > the PCIe bus from dma channel hardware. > > To a remote initiator, DMA_DEV_TO_MEM means using a remote dma WRITE > channel to transfer from remote memory to local memory. A WRITE channel > would be employed on the remote device in order to move the contents of > remote memory to the bus destined for local memory. > > To a remote initiator, DMA_MEM_TO_DEV means using a remote dma READ > channel to transfer from local memory to remote memory. A READ channel > would be employed on the remote device in order to move the contents of > local memory to the bus destined for remote memory. > > >From the perspective of a local dma initiator who is co-located on the > same side of the PCIe bus as the dma channel hardware, the semantics of > dma device transfer are flipped. > > To a local initiator, DMA_DEV_TO_MEM means using a local dma READ channel > to transfer from remote memory to local memory. A READ channel would be > employed on the local device in order to move the contents of remote > memory to the bus destined for local memory. > > To a local initiator, DMA_MEM_TO_DEV means using a local dma WRITE channel > to transfer from local memory to remote memory. A WRITE channel would be > employed on the local device in order to move the contents of local memory > to the bus destined for remote memory. > > To support local dma initiators, dw_edma_device_transfer() is modified to > now examine the direction field of struct dma_slave_config for the channel > which initiators can configure by calling dmaengine_slave_config(). > > If direction is configured as either DMA_DEV_TO_MEM or DMA_MEM_TO_DEV, > local initiator semantics are used. If direction is a value other than > DMA_DEV_TO_MEM nor DMA_MEM_TO_DEV, then remote initiator semantics are > used. This should maintain backward compatibility with the original use > case of dw-edma. > > The dw-edma-test utility is an example of a remote initiator. From reading > its patch, dw-edma-test does not specifically set the direction field of > struct dma_slave_config. Since dw_edma_device_transfer() also does not > check the direction field of struct dma_slave_config, it seems safe to use > this convention in dw-edma to support both local and remote initiator > semantics. Applied, thanks -- ~Vinod
