On Sat, Dec 24, 2016 at 05:47:19PM +0200, Ran Shalit wrote: > > > On Tue, Dec 20, 2016 at 12:26 PM, Greg KH <greg@xxxxxxxxx> wrote: > > On Tue, Dec 20, 2016 at 12:15:22PM +0200, Ran Shalit wrote: > > On Tue, Dec 20, 2016 at 11:38 AM, Greg KH <greg@xxxxxxxxx> wrote: > > > On Mon, Dec 19, 2016 at 06:08:47PM +0200, Ran Shalit wrote: > > >> Hello, > > >> > > >> I want to use DMA from userspace. > > > > > > Why? > > > > Hi Greg, > > > > We want that a userspace layer (a library) will do some HW related > issues. > > We have a memory mapped space (from FPGA), so we think it will be > > easier, and I think also more correct way , that we create the driver, > > and interact hadrware using the mapped memory space, and also do the > > protocols in userspace. The only thing that is less easy in userspace > > is using interrupt, and dma. but that is also possible if we just wrap > > the dma, and interrupt in a character device (or use uio as you > > suggested below). > > > > > >> I already use dma in kernel, and now I want can create a character > > >> device which will be responsible for this. > > > > > > Why? > > > > > >> The only problem is that I want to use the same memory which was > > >> allocated in kernel with dma_alloc_coherent. > > > > > > Why? > > > > in kernel we use dma_alloc_coherent, which returns contiguous memory. > > As I understand, we can mmap in userspace the returned physical > > address, and use the returned virtual address in userspace. > > > > > > > > > >> Is it correct to use mmap in order to use the phsyical memory which > > >> was allocated with dma_alloc_coherent ? > > >> > > >> If it's that simple it can be surely helpful, and the simple driver > > >> which wraps dma_alloc_coherent can do the job for dmaing from > > >> userspace. > > > > > > Have you looked at the uio driver interface? > > > > > > But again, why? What problem are you trying to solve here? > > > > We need to do some interaction with HW , but since most of the HW is > > mapped to physical address (FPGA), it seem simpler to do that in > > userspace (HW library), instead of doing this in kernel. What do you > > think ? > > I think you should use the UIO driver api, as that's exactly what it was > written for. Have you looked at it yet? It handles your interrupt > logic for you. > > > Hello, > > If I may please ask, I made some reading about uio, but didn't yet understand > what's the benefit of using uio instead of creating a character device ? It's a lot less work than writing a custom char driver that will not be accepted upstream because you are not using the expected UIO api interface :) Writing a UIO driver should be very simple, and very small, all of the framework is already done, in a correct way, why would you _not_ want to use the UIO interface? thanks, greg k-h _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
