Driver to allow DMA from user space

Driver to allow DMA from user space

[Ran Shalit]

Hello,

I want to use DMA from userspace.

I already use dma in kernel, and now I want can create a character
device which will be responsible for this.

The only problem is that I want to use the same memory which was
allocated in kernel with dma_alloc_coherent.

Is it correct to use mmap in order to use the phsyical memory which
was allocated with dma_alloc_coherent ?

If it's that simple it can be surely helpful, and the simple driver
which wraps dma_alloc_coherent can do the job for dmaing from
userspace.

In kernel:

dma_buffer_info->buf_info[i].virtAddr = (uint8_t *)dma_alloc_coherent(

                &ti667x_pci_dev[dev_id]->dev,

                dma_buffer_info->buffer_size,

                (dma_addr_t *)&dma_buffer_info->buf_info[i].pcieAddr,

                GFP_KERNEL);

In userspace:

buf_desc[i].virtAddr = mmap(0,

            size_of_buffer,

            PROT_READ | PROT_WRITE,

            MAP_SHARED,

            pcie_drv_inst[dsp_id].dev_desc,

            buf_desc[i].pcieAddr);

Thanks,
Ran

Driver to allow DMA from user space

[Greg KH]

On Mon, Dec 19, 2016 at 06:08:47PM +0200, Ran Shalit wrote:
> Hello,
> 
> I want to use DMA from userspace.

Why?

> I already use dma in kernel, and now I want can create a character
> device which will be responsible for this.

Why?

> The only problem is that I want to use the same memory which was
> allocated in kernel with dma_alloc_coherent.

Why?

> Is it correct to use mmap in order to use the phsyical memory which
> was allocated with dma_alloc_coherent ?
> 
> If it's that simple it can be surely helpful, and the simple driver
> which wraps dma_alloc_coherent can do the job for dmaing from
> userspace.

Have you looked at the uio driver interface?

But again, why?  What problem are you trying to solve here?

thanks,

greg k-h

Driver to allow DMA from user space

[Ran Shalit]

On Tue, Dec 20, 2016 at 11:38 AM, Greg KH <greg@kroah.com> wrote:
> On Mon, Dec 19, 2016 at 06:08:47PM +0200, Ran Shalit wrote:
>> Hello,
>>
>> I want to use DMA from userspace.
>
> Why?

Hi Greg,

We want that a userspace layer (a library) will do some HW related issues.
We have a memory mapped space (from FPGA), so we think it will be
easier, and I think also more correct way , that we create the driver,
and interact hadrware using the mapped memory space, and also do the
protocols in userspace. The only thing that is less easy in userspace
is using interrupt, and dma. but that is also possible if we just wrap
the dma, and interrupt in a character device (or use uio as you
suggested below).
>
>> I already use dma in kernel, and now I want can create a character
>> device which will be responsible for this.
>
> Why?
>
>> The only problem is that I want to use the same memory which was
>> allocated in kernel with dma_alloc_coherent.
>
> Why?

in kernel we use dma_alloc_coherent, which returns contiguous memory.
As I understand, we can mmap in userspace the returned  physical
address, and use the returned virtual address in userspace.


>
>> Is it correct to use mmap in order to use the phsyical memory which
>> was allocated with dma_alloc_coherent ?
>>
>> If it's that simple it can be surely helpful, and the simple driver
>> which wraps dma_alloc_coherent can do the job for dmaing from
>> userspace.
>
> Have you looked at the uio driver interface?
>
> But again, why?  What problem are you trying to solve here?

We need to do some interaction with HW , but since most of the HW is
mapped to physical address (FPGA), it seem simpler to do that in
userspace (HW library), instead of doing this in kernel. What do you
think ?


>
> thanks,
>
> greg k-h

Driver to allow DMA from user space

[Greg KH]

On Tue, Dec 20, 2016 at 12:15:22PM +0200, Ran Shalit wrote:
> On Tue, Dec 20, 2016 at 11:38 AM, Greg KH <greg@kroah.com> wrote:
> > On Mon, Dec 19, 2016 at 06:08:47PM +0200, Ran Shalit wrote:
> >> Hello,
> >>
> >> I want to use DMA from userspace.
> >
> > Why?
> 
> Hi Greg,
> 
> We want that a userspace layer (a library) will do some HW related issues.
> We have a memory mapped space (from FPGA), so we think it will be
> easier, and I think also more correct way , that we create the driver,
> and interact hadrware using the mapped memory space, and also do the
> protocols in userspace. The only thing that is less easy in userspace
> is using interrupt, and dma. but that is also possible if we just wrap
> the dma, and interrupt in a character device (or use uio as you
> suggested below).
> >
> >> I already use dma in kernel, and now I want can create a character
> >> device which will be responsible for this.
> >
> > Why?
> >
> >> The only problem is that I want to use the same memory which was
> >> allocated in kernel with dma_alloc_coherent.
> >
> > Why?
> 
> in kernel we use dma_alloc_coherent, which returns contiguous memory.
> As I understand, we can mmap in userspace the returned  physical
> address, and use the returned virtual address in userspace.
> 
> 
> >
> >> Is it correct to use mmap in order to use the phsyical memory which
> >> was allocated with dma_alloc_coherent ?
> >>
> >> If it's that simple it can be surely helpful, and the simple driver
> >> which wraps dma_alloc_coherent can do the job for dmaing from
> >> userspace.
> >
> > Have you looked at the uio driver interface?
> >
> > But again, why?  What problem are you trying to solve here?
> 
> We need to do some interaction with HW , but since most of the HW is
> mapped to physical address (FPGA), it seem simpler to do that in
> userspace (HW library), instead of doing this in kernel. What do you
> think ?

I think you should use the UIO driver api, as that's exactly what it was
written for.  Have you looked at it yet?  It handles your interrupt
logic for you.

thanks,

greg k-h

Driver to allow DMA from user space

[Ran Shalit]

On Tue, Dec 20, 2016 at 12:26 PM, Greg KH <greg@kroah.com> wrote:

> On Tue, Dec 20, 2016 at 12:15:22PM +0200, Ran Shalit wrote:
> > On Tue, Dec 20, 2016 at 11:38 AM, Greg KH <greg@kroah.com> wrote:
> > > On Mon, Dec 19, 2016 at 06:08:47PM +0200, Ran Shalit wrote:
> > >> Hello,
> > >>
> > >> I want to use DMA from userspace.
> > >
> > > Why?
> >
> > Hi Greg,
> >
> > We want that a userspace layer (a library) will do some HW related
> issues.
> > We have a memory mapped space (from FPGA), so we think it will be
> > easier, and I think also more correct way , that we create the driver,
> > and interact hadrware using the mapped memory space, and also do the
> > protocols in userspace. The only thing that is less easy in userspace
> > is using interrupt, and dma. but that is also possible if we just wrap
> > the dma, and interrupt in a character device (or use uio as you
> > suggested below).
> > >
> > >> I already use dma in kernel, and now I want can create a character
> > >> device which will be responsible for this.
> > >
> > > Why?
> > >
> > >> The only problem is that I want to use the same memory which was
> > >> allocated in kernel with dma_alloc_coherent.
> > >
> > > Why?
> >
> > in kernel we use dma_alloc_coherent, which returns contiguous memory.
> > As I understand, we can mmap in userspace the returned  physical
> > address, and use the returned virtual address in userspace.
> >
> >
> > >
> > >> Is it correct to use mmap in order to use the phsyical memory which
> > >> was allocated with dma_alloc_coherent ?
> > >>
> > >> If it's that simple it can be surely helpful, and the simple driver
> > >> which wraps dma_alloc_coherent can do the job for dmaing from
> > >> userspace.
> > >
> > > Have you looked at the uio driver interface?
> > >
> > > But again, why?  What problem are you trying to solve here?
> >
> > We need to do some interaction with HW , but since most of the HW is
> > mapped to physical address (FPGA), it seem simpler to do that in
> > userspace (HW library), instead of doing this in kernel. What do you
> > think ?
>
> I think you should use the UIO driver api, as that's exactly what it was
> written for.  Have you looked at it yet?  It handles your interrupt
> logic for you.
>
> Hello,

If I may please ask, I made some reading about uio, but didn't yet
understand what's the benefit of using uio instead of creating a character
device ?

Thanks,
Ran


thanks,
>
> greg k-h
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20161224/0b529703/attachment-0001.html 

Driver to allow DMA from user space

[Greg KH]

On Sat, Dec 24, 2016 at 05:47:19PM +0200, Ran Shalit wrote:
> 
> 
> On Tue, Dec 20, 2016 at 12:26 PM, Greg KH <greg@kroah.com> wrote:
> 
>     On Tue, Dec 20, 2016 at 12:15:22PM +0200, Ran Shalit wrote:
>     > On Tue, Dec 20, 2016 at 11:38 AM, Greg KH <greg@kroah.com> wrote:
>     > > On Mon, Dec 19, 2016 at 06:08:47PM +0200, Ran Shalit wrote:
>     > >> Hello,
>     > >>
>     > >> I want to use DMA from userspace.
>     > >
>     > > Why?
>     >
>     > Hi Greg,
>     >
>     > We want that a userspace layer (a library) will do some HW related
>     issues.
>     > We have a memory mapped space (from FPGA), so we think it will be
>     > easier, and I think also more correct way , that we create the driver,
>     > and interact hadrware using the mapped memory space, and also do the
>     > protocols in userspace. The only thing that is less easy in userspace
>     > is using interrupt, and dma. but that is also possible if we just wrap
>     > the dma, and interrupt in a character device (or use uio as you
>     > suggested below).
>     > >
>     > >> I already use dma in kernel, and now I want can create a character
>     > >> device which will be responsible for this.
>     > >
>     > > Why?
>     > >
>     > >> The only problem is that I want to use the same memory which was
>     > >> allocated in kernel with dma_alloc_coherent.
>     > >
>     > > Why?
>     >
>     > in kernel we use dma_alloc_coherent, which returns contiguous memory.
>     > As I understand, we can mmap in userspace the returned? physical
>     > address, and use the returned virtual address in userspace.
>     >
>     >
>     > >
>     > >> Is it correct to use mmap in order to use the phsyical memory which
>     > >> was allocated with dma_alloc_coherent ?
>     > >>
>     > >> If it's that simple it can be surely helpful, and the simple driver
>     > >> which wraps dma_alloc_coherent can do the job for dmaing from
>     > >> userspace.
>     > >
>     > > Have you looked at the uio driver interface?
>     > >
>     > > But again, why?? What problem are you trying to solve here?
>     >
>     > We need to do some interaction with HW , but since most of the HW is
>     > mapped to physical address (FPGA), it seem simpler to do that in
>     > userspace (HW library), instead of doing this in kernel. What do you
>     > think ?
> 
>     I think you should use the UIO driver api, as that's exactly what it was
>     written for.? Have you looked at it yet?? It handles your interrupt
>     logic for you.
> 
> 
> Hello,
> 
> If I may please ask, I made some reading about uio, but didn't yet understand
> what's the benefit of using uio instead of creating a character device ??

It's a lot less work than writing a custom char driver that will not be
accepted upstream because you are not using the expected UIO api
interface :)

Writing a UIO driver should be very simple, and very small, all of the
framework is already done, in a correct way, why would you _not_ want to
use the UIO interface?

thanks,

greg k-h

Driver to allow DMA from user space

[Ran Shalit]

On Sun, Dec 25, 2016 at 2:37 PM, Greg KH <greg@kroah.com> wrote:
> On Sat, Dec 24, 2016 at 05:47:19PM +0200, Ran Shalit wrote:
>>
>>
>> On Tue, Dec 20, 2016 at 12:26 PM, Greg KH <greg@kroah.com> wrote:
>>
>> On Tue, Dec 20, 2016 at 12:15:22PM +0200, Ran Shalit wrote:
>> > On Tue, Dec 20, 2016 at 11:38 AM, Greg KH <greg@kroah.com> wrote:
>> > > On Mon, Dec 19, 2016 at 06:08:47PM +0200, Ran Shalit wrote:
>> > >> Hello,
>> > >>
>> > >> I want to use DMA from userspace.
>> > >
>> > > Why?
>> >
>> > Hi Greg,
>> >
>> > We want that a userspace layer (a library) will do some HW related
>> issues.
>> > We have a memory mapped space (from FPGA), so we think it will be
>> > easier, and I think also more correct way , that we create the driver,
>> > and interact hadrware using the mapped memory space, and also do the
>> > protocols in userspace. The only thing that is less easy in userspace
>> > is using interrupt, and dma. but that is also possible if we just wrap
>> > the dma, and interrupt in a character device (or use uio as you
>> > suggested below).
>> > >
>> > >> I already use dma in kernel, and now I want can create a character
>> > >> device which will be responsible for this.
>> > >
>> > > Why?
>> > >
>> > >> The only problem is that I want to use the same memory which was
>> > >> allocated in kernel with dma_alloc_coherent.
>> > >
>> > > Why?
>> >
>> > in kernel we use dma_alloc_coherent, which returns contiguous memory.
>> > As I understand, we can mmap in userspace the returned physical
>> > address, and use the returned virtual address in userspace.
>> >
>> >
>> > >
>> > >> Is it correct to use mmap in order to use the phsyical memory which
>> > >> was allocated with dma_alloc_coherent ?
>> > >>
>> > >> If it's that simple it can be surely helpful, and the simple driver
>> > >> which wraps dma_alloc_coherent can do the job for dmaing from
>> > >> userspace.
>> > >
>> > > Have you looked at the uio driver interface?
>> > >
>> > > But again, why? What problem are you trying to solve here?
>> >
>> > We need to do some interaction with HW , but since most of the HW is
>> > mapped to physical address (FPGA), it seem simpler to do that in
>> > userspace (HW library), instead of doing this in kernel. What do you
>> > think ?
>>
>> I think you should use the UIO driver api, as that's exactly what it was
>> written for. Have you looked at it yet? It handles your interrupt
>> logic for you.
>>
>>
>> Hello,
>>
>> If I may please ask, I made some reading about uio, but didn't yet
understand
>> what's the benefit of using uio instead of creating a character device ?
>
> It's a lot less work than writing a custom char driver that will not be
> accepted upstream because you are not using the expected UIO api
> interface :)
>
> Writing a UIO driver should be very simple, and very small, all of the
> framework is already done, in a correct way, why would you _not_ want to
> use the UIO interface?
>
Hi,

UIO drivers seems like a good choice in my case, I am familiar with
generic-uio interface in devicetree.
Just for my understanding, I am trying to understand the difference between
writing a small character device which notifies the interrupt, to using uio
interface.
Is there any advantage of using uio over the the small chracter device?(I
am sure there is. I just do not know it yet)
Another question, in performance terms which is better: uio driver or
kernel driver?

Thank you,
Ran

> thanks,
>
> greg k-h
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20161230/40d3c481/attachment.html 

Driver to allow DMA from user space

[Greg KH]

On Fri, Dec 30, 2016 at 08:11:56PM +0200, Ran Shalit wrote:
> On Sun, Dec 25, 2016 at 2:37 PM, Greg KH <greg@kroah.com> wrote:
> > On Sat, Dec 24, 2016 at 05:47:19PM +0200, Ran Shalit wrote:
> >>
> >>
> >> On Tue, Dec 20, 2016 at 12:26 PM, Greg KH <greg@kroah.com> wrote:
> >>
> >> On Tue, Dec 20, 2016 at 12:15:22PM +0200, Ran Shalit wrote:
> >> > On Tue, Dec 20, 2016 at 11:38 AM, Greg KH <greg@kroah.com> wrote:
> >> > > On Mon, Dec 19, 2016 at 06:08:47PM +0200, Ran Shalit wrote:
> >> > >> Hello,
> >> > >>
> >> > >> I want to use DMA from userspace.
> >> > >
> >> > > Why?
> >> >
> >> > Hi Greg,
> >> >
> >> > We want that a userspace layer (a library) will do some HW related
> >> issues.
> >> > We have a memory mapped space (from FPGA), so we think it will be
> >> > easier, and I think also more correct way , that we create the driver,
> >> > and interact hadrware using the mapped memory space, and also do the
> >> > protocols in userspace. The only thing that is less easy in userspace
> >> > is using interrupt, and dma. but that is also possible if we just wrap
> >> > the dma, and interrupt in a character device (or use uio as you
> >> > suggested below).
> >> > >
> >> > >> I already use dma in kernel, and now I want can create a character
> >> > >> device which will be responsible for this.
> >> > >
> >> > > Why?
> >> > >
> >> > >> The only problem is that I want to use the same memory which was
> >> > >> allocated in kernel with dma_alloc_coherent.
> >> > >
> >> > > Why?
> >> >
> >> > in kernel we use dma_alloc_coherent, which returns contiguous memory.
> >> > As I understand, we can mmap in userspace the returned physical
> >> > address, and use the returned virtual address in userspace.
> >> >
> >> >
> >> > >
> >> > >> Is it correct to use mmap in order to use the phsyical memory which
> >> > >> was allocated with dma_alloc_coherent ?
> >> > >>
> >> > >> If it's that simple it can be surely helpful, and the simple driver
> >> > >> which wraps dma_alloc_coherent can do the job for dmaing from
> >> > >> userspace.
> >> > >
> >> > > Have you looked at the uio driver interface?
> >> > >
> >> > > But again, why? What problem are you trying to solve here?
> >> >
> >> > We need to do some interaction with HW , but since most of the HW is
> >> > mapped to physical address (FPGA), it seem simpler to do that in
> >> > userspace (HW library), instead of doing this in kernel. What do you
> >> > think ?
> >>
> >> I think you should use the UIO driver api, as that's exactly what it was
> >> written for. Have you looked at it yet? It handles your interrupt
> >> logic for you.
> >>
> >>
> >> Hello,
> >>
> >> If I may please ask, I made some reading about uio, but didn't yet
> understand
> >> what's the benefit of using uio instead of creating a character device ?
> >
> > It's a lot less work than writing a custom char driver that will not be
> > accepted upstream because you are not using the expected UIO api
> > interface :)
> >
> > Writing a UIO driver should be very simple, and very small, all of the
> > framework is already done, in a correct way, why would you _not_ want to
> > use the UIO interface?
> >
> Hi,
> 
> UIO drivers seems like a good choice in my case, I am familiar with generic-uio
> interface in devicetree.
> Just for my understanding, I am trying to understand the difference between
> writing a small character device which notifies the interrupt, to using uio
> interface.

Have you tried it?

> Is there any advantage of using uio over the the small chracter device?(I am
> sure there is. I just do not know it yet)

Try it, doing it "correctly" with a char driver will force you to
reimplement everything we did for the UIO layer.  It was written for a
reason (i.e. we got tired of seeing everyone do it totally wrong and
causing bugs).

> Another question, in performance terms which is better: uio driver or kernel
> driver?

Depends on your hardware and your application, and uio _is_ a kernel
driver.

Again, try it out and see.

thanks,

greg k-h