GSoC Linux UIO driver for PRU

[Sebastian Huber]

On 14/07/2019 01:34, Joel Sherrill wrote:
> On Sat, Jul 13, 2019 at 1:42 PM Chris Johns <chrisj at rtems.org 
> <mailto:chrisj at rtems.org>> wrote:
> 
> 
> 
>     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.
> 
> 
> There is a helper in the IO Manager which is implemented as a call to 
> mknod()
> which is a standard call.


In libbsd devices should be added with IMFS_make_generic_node():

freebsd/sys/net/bpf.c:  rv = IMFS_make_generic_node("/dev/bpf", mode, 
&bpf_imfs_control, NULL);
freebsd/sys/kern/uipc_usrreq.c: rv = IMFS_make_generic_node(soun->sun_path,
rtemsbsd/sys/fs/devfs/devfs_devs.c:     rv = 
IMFS_make_generic_node(dev->si_path, mode, &devfs_imfs_control,

-- 
Sebastian Huber, embedded brains GmbH

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