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

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Message-ID: <20200622065727.ywbnevdhjs7kizfc@cwe-513-vol689.cern.ch>
Date:   Mon, 22 Jun 2020 08:57:27 +0200
From:   Federico Vaga <federico.vaga@...n.ch>
To:     Vinod Koul <vkoul@...nel.org>
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 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