UIO Kernel Driver with Buildroot and QEMU

[Kenneth Adam Miller]

On Tue, Oct 20, 2015 at 6:54 PM, Greg KH <greg at kroah.com> wrote:

> On Tue, Oct 20, 2015 at 11:58:21AM -0400, Kenneth Adam Miller wrote:
> > So I'm building a uio kernel driver with buildroot, and I've gotten the
> driver
> > to compile, installed it and can insmod it in the final buildroot target
> after
> > booting the image with QEMU.
> >
> > I'm on linux kernel version 3.14, and I followed the guide here:
> >
> > https://www.kernel.org/doc/htmldocs/uio-howto/userspace_driver.html
> >
> > And it describes the location on where the device file that should be
> opened by
> > userland code as either one of two locations:
> >
> > /dev/uioX, with X being a number
> >
> > or /sys/class/uio/uioX
> >
> > But the each of following returns nothing:
> >
> > ls /dev/uio*
> > ls /sys/class/uio/
> >
> > After I compile the uio example that is provided in the linux source at
> source/
> > drivers/uio/uio.c and uio_dmem_genirq.c, and insmod them, I do modprobe
> uio and
> > modprobe uio_dmem_genirq and each of those return nothing. However, I do
> see
> > that /sys/modules/uio and /sys/modules/uio_dmem_genirq
>
> uio.ko is the uio "core", you need a uio driver in order to actually use
> it.
>
> uio_dmem_genirq is a uio driver, have you added the needed device tree
> entries to have it actually create a device for you?  Without them, this
> driver can not find any hardware to bind to, and as such, no device node
> will ever be created.
>

I didn't know about that. How do I do that? I'm using buildroot; I guess
there's something missing in menuconfig or linux-menuconfig.


>
> I would suggest reading the UIO documentation, it should explain all of
> this for you already.  If not, specific questions are always gladly
> answered.
>

The one that I linked? I read that repeatedly. What other documentation is
there to read? I also read from Essential Linux Device Drivers, and none of
them explained that. There has to be something I'm missing.

Thanks a lot!


>
> thanks,
>
> greg k-h
>
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