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

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Date:   Tue, 12 Sep 2017 05:37:16 -0700
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     Joakim Tjernlund <Joakim.Tjernlund@...inera.com>
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, 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?

thanks,

greg k-h