linux-kernel - Re: DMA Engine: Transfer From Userspace

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Message-ID: <20200622044733.GB2324254@vkoul-mobl>
Date:   Mon, 22 Jun 2020 10:17:33 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Federico Vaga <federico.vaga@...n.ch>
Cc:     Dave Jiang <dave.jiang@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: DMA Engine: Transfer From Userspace

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?

-- 
~Vinod