PCI Express and drivers

[Daniel O'Connor]

On 26/06/2010, at 3:01, Christopher Bowman wrote:
> I have a Xilinx PCI Express board that has an on board PCIe interface
> macro.  I intend to have an address space with memory and another with my
> devices control registers.  I wish to program this board under FreeBSD.  It
> would seem to me that the way to do this would be to write a driver that
> would allow me to map these two address spaces into a user process which
> could then directly interact with the device.  In my case my board doesn't
> really support multiple users, and it doesn't really seem to make sense to
> me to put a lot of code in the kernel to create some sort of interface to
> allow multiple processes to interact with my device via some sort of syscall
> which would impose a lot of overhead in any case.  By mapping the address
> ranges into a user process I can write user programs to drive the board
> without having to recompile and reboot the kernel each time I make a change,
> plus if I do something stupid and crash my user space process it shouldn't
> bring down the whole kernel.  Am I thinking about this wrong?  Is there some
> place I can go to read up on what I should be doing?  If I am thinking about
> this correctly, then how does one map device memory into a user space
> process?  How does one make sure that only one process has such a mapping?

You could use mmap() I think,

For a driver I maintain I did the following ->
 /* Magic sauce stolen from src/sys/pci/xrpu.c via phk
  * http://www.mail-archive.com/freebsd-hackers%40freebsd.org/msg11729.html
  */
  *paddr = rman_get_start(sc->g_membase.reshandle) + offset;
    
g_membase is..
    struct resource	*reshandle;	/* Resource handle */
    bus_space_tag_t	sc_st;		/* bus space tag */
    bus_space_handle_t	sc_sh;		/* bus space handle */

PS what board are you using? :)

--
Daniel O'Connor software and network engineer
for Genesis Software - http://www.gsoft.com.au
"The nice thing about standards is that there
are so many of them to choose from."
  -- Andrew Tanenbaum
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