Re: DMA Engine: Transfer From Userspace

[Federico Vaga]

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)

> Federico, what use case do you have in mind?

Userspace drivers

> We should keep in mind dmaengine is an in-kernel interface providing
> services to various subsystems, so you go thru the respective subsystem
> kernel interface (network, display, spi, audio etc..) which would in
> turn use dmaengine.
>
> --
> ~Vinod