On Wed, Jul 02, 2014 at 11:39:36AM +0530, Raghavendra wrote: > On Wednesday 02 July 2014 11:42 AM, Greg KH wrote: > >On Wed, Jul 02, 2014 at 11:32:47AM +0530, Raghavendra wrote: > >>On Wednesday 02 July 2014 11:02 AM, Greg KH wrote: > >>>On Tue, Jul 01, 2014 at 10:29:39PM -0700, Greg KH wrote: > >>>>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? > >>>Also, you _have_ read the USB DMA documentation, right? > >>> > >>>What about the documentation in this area is unclear? > >>Yes, I have read the documentation and its fine. I am mostly concerned about > >>the all the heavy lifting happening in the background. > >Why? What exactly are you "concerned" about? What hardware controller? > >Is something not working properly? > Everything is fine. This is more of a theoretical understanding. The code is there for your theoretical research :) _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
