> On 22 June 2020 at 14:30 Federico Vaga <federico.vaga@xxxxxxx> wrote: > > > On Mon, Jun 22, 2020 at 02:01:12PM +0200, Thomas Ruf wrote: > >> On 22 June 2020 at 06:47 Vinod Koul <vkoul@xxxxxxxxxx> wrote: > >> > >> On 21-06-20, 22:36, Federico Vaga wrote: > >> > On Sun, Jun 21, 2020 at 12:54:57PM +0530, Vinod Koul wrote: > >> > > On 19-06-20, 16:31, Dave Jiang wrote: > >> > > > > >> > > > > >> > > > On 6/19/2020 3:47 PM, Federico Vaga wrote: > >> > > > > Hello, > >> > > > > > >> > > > > is there the possibility of using a DMA engine channel from userspace? > >> > > > > > >> > > > > Something like: > >> > > > > - configure DMA using ioctl() (or whatever configuration mechanism) > >> > > > > - read() or write() to trigger the transfer > >> > > > > > >> > > > > >> > > > I may have supposedly promised Vinod to look into possibly providing > >> > > > something like this in the future. But I have not gotten around to do that > >> > > > yet. Currently, no such support. > >> > > > >> > > And I do still have serious reservations about this topic :) Opening up > >> > > userspace access to DMA does not sound very great from security point of > >> > > view. > >> > > >> > I was thinking about a dedicated module, and not something that the DMA engine > >> > offers directly. You load the module only if you need it (like the test module) > >> > >> But loading that module would expose dma to userspace. > >> > > >> > > Federico, what use case do you have in mind? > >> > > >> > Userspace drivers > >> > >> more the reason not do do so, why cant a kernel driver be added for your > >> usage? > > > >by chance i have written a driver allowing dma from user space using a memcpy like interface ;-) > >now i am trying to get this code upstream but was hit by the fact that DMA_SG is gone since Aug 2017 :-( > > Not sure to get what you mean by "DMA_SG is gone". Can I have a reference? here the link to the mailinglist when DMA_SG was removed: https://www.spinics.net/lists/dmaengine/msg13778.html > >just let me introduce myself and the project: > >- coding in C since '91 > >- coding in C++ since '98 > >- a lot of stuff not relevant for this ;-) > >- working as a freelancer since Nov '19 > >- implemented a "dma-sg-proxy" driver for my client in Mar/Apr '20 to copy camera frames from uncached memory to cached memory using a second dma on a Zynq platform > >- last week we figured out that we can not upgrade from "Xilinx 2019.2" (kernel 4.19.x) to "2020.1" (kernel 5.4.x) because the DMA_SG interface is gone > >- subscribed to dmaengine on friday, saw the start of this discussion on saturday > >- talked to my client today if it is ok to try to revive DMA_SG and get our driver upstream to avoid such problems in future > > > >here the struct for the ioctl: > > > >typedef struct { > > unsigned int struct_size; > > const void *src_user_ptr; > > void *dst_user_ptr; > > unsigned long length; > > unsigned int timeout_in_ms; > >} dma_sg_proxy_arg_t; > > Yes, roughly this is what I was thinking about cool, i really hope i get my stuff upstream! Best regards, Thomas
