Re: DMA Engine: Transfer From Userspace

[Federico Vaga]

On Mon, Jun 22, 2020 at 10:17:33AM +0530, Vinod Koul 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.

Of course, but users *should* know what they are doing ... right? ^_^'

> > > 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?

Yes of course, I was just wandering if there was a kernel API.

> --
> ~Vinod