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From: Federico Vaga <federico.vaga@cern.ch>
To: Thomas Ruf <freelancer@rufusul.de>
Cc: Vinod Koul <vkoul@kernel.org>, Dave Jiang <dave.jiang@intel.com>,
	"Dan Williams" <dan.j.williams@intel.com>,
	<dmaengine@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: DMA Engine: Transfer From Userspace
Date: Mon, 22 Jun 2020 14:30:19 +0200
Message-ID: <20200622123019.z3i2tjcfliwkbzkx@cwe-513-vol689.cern.ch> (raw)
In-Reply-To: <419762761.402939.1592827272368@mailbusiness.ionos.de>

On Mon, Jun 22, 2020 at 02:01:12PM +0200, Thomas Ruf wrote:
>> On 22 June 2020 at 06:47 Vinod Koul <vkoul@kernel.org> 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.
>> >
>> > > 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?
>
>by chance i have written a driver allowing dma from user space using a memcpy like interface ;-)
>now i am trying to get this code upstream but was hit by the fact that DMA_SG is gone since Aug 2017 :-(

Not sure to get what you mean by "DMA_SG is gone". Can I have a reference?

>
>just let me introduce myself and the project:
>- coding in C since '91
>- coding in C++ since '98
>- a lot of stuff not relevant for this ;-)
>- working as a freelancer since Nov '19
>- implemented a "dma-sg-proxy" driver for my client in Mar/Apr '20 to copy camera frames from uncached memory to cached memory using a second dma on a Zynq platform
>- last week we figured out that we can not upgrade from "Xilinx 2019.2" (kernel 4.19.x) to "2020.1" (kernel 5.4.x) because the DMA_SG interface is gone
>- subscribed to dmaengine on friday, saw the start of this discussion on saturday
>- talked to my client today if it is ok to try to revive DMA_SG and get our driver upstream to avoid such problems in future
>
>here the struct for the ioctl:
>
>typedef struct {
>  unsigned int struct_size;
>  const void *src_user_ptr;
>  void *dst_user_ptr;
>  unsigned long length;
>  unsigned int timeout_in_ms;
>} dma_sg_proxy_arg_t;

Yes, roughly this is what I was thinking about

>best regards,
>Thomas

  parent reply index

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-19 22:47 Federico Vaga
2020-06-19 23:31 ` Dave Jiang
2020-06-21  7:24   ` Vinod Koul
2020-06-21 20:36     ` Federico Vaga
2020-06-21 20:45       ` Richard Weinberger
2020-06-21 22:32         ` Federico Vaga
2020-06-22  4:47       ` Vinod Koul
2020-06-22  6:57         ` Federico Vaga
2020-06-22 12:01         ` Thomas Ruf
2020-06-22 12:27           ` Richard Weinberger
2020-06-22 14:01             ` Thomas Ruf
2020-06-22 12:30           ` Federico Vaga [this message]
2020-06-22 14:03             ` Thomas Ruf
2020-06-22 15:54           ` Vinod Koul
2020-06-22 16:34             ` Thomas Ruf
2020-06-24  9:30               ` Thomas Ruf
2020-06-24  9:38                 ` Vinod Koul
2020-06-24 12:07                   ` Peter Ujfalusi
2020-06-24 13:58                     ` Thomas Ruf
2020-06-26 10:29                       ` Peter Ujfalusi
2020-06-29 15:18                         ` Thomas Ruf
2020-06-30 12:31                           ` Peter Ujfalusi
2020-07-01 16:13                             ` Thomas Ruf
2020-06-25  0:42     ` Dave Jiang
2020-06-25  8:11       ` Thomas Ruf
2020-06-26 20:08         ` Ira Weiny
2020-06-29 15:31           ` Thomas Ruf
2020-06-22  9:25 ` Federico Vaga
2020-06-22  9:42   ` Vinod Koul

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