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

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Message-ID: <20200621203634.y3tejmh6j4knf5iz@cwe-513-vol689.cern.ch>
Date:   Sun, 21 Jun 2020 22:36:34 +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 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