On Wed, Jul 02, 2014 at 10:40:21AM +0530, Raghavendra wrote: > Hello, > > I have a query regarding DMA(Direct Memory Access) for the usb devices. > > The understanding of DMA actions over PCI is straight forward. PCI > devices support bus mastering capability, such that the PCI devices > could take the ownership of the bus and perform access to the memory > directly, and a software support exists for the same in Linux. > > As far as USB devices are concerned, they don’t have the bus mastering > capability like the PCI devices. > But the USB URB structure have a field named 'dma_addr_t transfer_dma', > used for DMA access. The USB driver allocate the DMA buffers coherently > and pass the DMA address to the URBs during its initialization. > As far as Linux is concerned, how the DMA action being taking place for > USB devices. As per my understanding, the USB host controller is taking > care of the DMA operations. But I require a little more insight into it. Why, what exactly are you concerned about? What are you trying to do? > Further more, if it is possible for the USB devices, then can this > support be also extended towards low-end protocols such as I2C or SPI? It depends on your controller chips for those busses, if they support DMA or not. greg k-h _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
