linux-kernel - Re: uio_dmem_genirq.c and DMA mapping to user space ?

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Date:   Tue, 12 Sep 2017 14:08:27 +0000
From:   Joakim Tjernlund <Joakim.Tjernlund@...inera.com>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: uio_dmem_genirq.c and DMA mapping to user space ?

On Tue, 2017-09-12 at 05:37 -0700, gregkh@...uxfoundation.org wrote:
> On Tue, Sep 12, 2017 at 12:18:27PM +0000, Joakim Tjernlund wrote:
> > Hi
> > 
> > I am trying to use the uio_dmem_genirq.c driver for allocating DMA memory to a PCI device
> > using the uio_pci_generic.c driver.
> > 
> > I got as far as defining an UIO dev containing only Dynamic DMA memory and
> > now I am stuck.
> > I can see how DMA memory is allocated when opening the /dev/uio device but I cannot
> > figure out how to mmap this memory to User space as well so I can share this
> > memory with the PCI device and my user space driver.
> > 
> > What am I missing?
> 
> Why can't you call mmap() on the fd you created when you opened
> /dev/uio?  What happens when you do that?

Haven't tried that as I figured it had to be something similar as UIO PCI
where you can have several memory regions and therefore must mmap one of
the resource files under sys:
# > pwd
/sys/bus/pci/drivers/uio_pci_generic/0000:01:00.0/uio/uio8/device
leipzig device # cat /sys/devices/platform/ffe250000.pcie/pci0000:00/0000:00:00.0/0000:01:00.0/resource
0x0000000c10000000 0x0000000c11ffffff 0x0000000000140204
0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 0x0000000000000000
leipzig device # pwd
/sys/bus/pci/drivers/uio_pci_generic/0000:01:00.0/uio/uio8/device
leipzig device # cat resource
0x0000000c10000000 0x0000000c11ffffff 0x0000000000140204
0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 0x0000000000000000
leipzig device # ls resource*
resource  resource0

Here one opens and mmaps resource0 to get at
 0x0000000c10000000 0x0000000c11ffffff 0x0000000000140204

 Jocke