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? greg k-h _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
