GSoC Linux UIO driver for PRU

[Chris Johns]

On 13/7/19 5:16 pm, Nils Hölscher wrote:
> Hi,
> 
> After I made sure that my fdt is correct I wondered why the pruss was still not
> accessible.
> When I researched more about userspace drivers in Linux I found out, that I have
> overseen the pru UIO module in Linux.
> This is the part that links the PRUs to the /dev/uio[0-7].
> Which then would be used by the sources I currently use.
> The UIO source is available here:
> https://github.com/beagleboard/linux/blob/3.8/drivers/uio/uio_pruss.c
> However this requires the linux UIO lib to load the modules and abstract the
> device into a file.
> 
> While researching I also found that BSD has a PRU driver.
> Also this driver is more feature rich as it support PRU debugging.
> The sources can be found her:
> https://bitbucket.org/rpaulo/libpru/src/default/
> Additionally I found these sources in the FreeBSD tree:
> https://github.com/freebsd/freebsd/blob/250e158ddf52459661439141407bca505d199c19/sys/arm/ti/ti_pruss.c
> This code also registers the PRUs in /dev/.
> On the other hand the BSD drivers have no documentation at all.
> 
> These are the code lines that will fail without a file in /dev.
> Linux: https://github.com/nilhoel1/rtems-pru/blob/master/ti/prussdrv.c#L265
> BSD: https://bitbucket.org/rpaulo/libpru/src/5cb7271533a96d177e73492f7cc40fa4b28396a5/ti-pru.c#lines-614
> 
> So my questions are:
> 1. How are drivers registered to /dev in RTEMS? (examples)

I suggest you look at cpukit/include/rtems/io.h and then for examples of this
interface being used in the bsp directory.

> 2. Which driver would be a better starting point to bring pruss support to RTEMS?

The bitbucket set of drivers look pretty good so I think just use them and add
to the beagle bsp.

Chris