Re: Memory mapping PCI memory region to user space

[Phil Nitschke <Phil.Nitschke@avalon.com.au>]

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On Mon, 2006-03-27 at 10:18 -0600, Kumar Gala wrote:
> On Mar 27, 2006, at 2:02 AM, Phil Nitschke wrote:
> 
> > On Thu, 2006-03-23 at 09:44 -0600, Kumar Gala wrote:
> >> On Mar 23, 2006, at 8:21 AM, Wyse, Chris wrote:
> >>
> >>> Hi,
> >>>
> >>> I'm trying to map a PCI memory region 1 into user space from my
> >>> driver (PPC440GX, Linux 2.6.10).  Here's the mmap routine of the
> >>> driver that I'm using:
> >>
> >> Why don't use the mmap file exposed by sysfs so you dont have to
> >> write your own code?
> >>
> >> See Documentation/filesystems/sysfs-pci.txt.  But effectively down
> >> under /sys/bus/pci/devices/[domain:bus:dev:func]/ you will get
> >> resource[0..N-1] that corresponds to each BAR on the device.  This is
> >> a mmap file to access that region.
> >
> > I have some custom hardware that appears on the PCI bus as follows:
> >
> > bash-3.00# lspci -vv
> > 00:01.0 Class 0680: 1172:0004 (rev 01)
> > 	Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr-
> > Stepping- SERR- FastB2B-
> > 	Status: Cap- 66Mhz+ UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort+
> > <TAbort- <MAbort- >SERR- <PERR-
> > 	Latency: 128, Cache Line Size 08
> > 	Interrupt: pin A routed to IRQ 71
> > 	Region 0: Memory at 000000009ffff000 (32-bit, non-prefetchable)
> > [size=4K]
> > 	Region 1: Memory at 000000009fc00000 (32-bit, non-prefetchable)
> > [size=2M]
> >
> > But when I try to access resource0 or resource1, I get a read error.
> > What characteristic of the device or driver determines whether it will
> > allow mmap-ing?
> >
> > (I've written the driver for this device myself.)
> 
> Nothing special beyond normal unix perms on the resource[0..n] files  
> to my knowledge.  When you say you get a read error what exactly does  
> that mean?

It means I had a bug in my program which read (mmap()ed) the resouce :-(
It is fixed now (see below).  Thanks for the tip.

-- 
Phil Nitschke <Phil.Nitschke@avalon.com.au>
Avalon Systems Pty Ltd



[-- Attachment #2: mmap.c --]
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#include <assert.h>
#include <byteswap.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <sys/mman.h>
#include <unistd.h>

int
main (int argc, char **argv)
{
  /* Define constants for specific to the Base Address Register(s)
   * (defining the PCI I/O Address Region) for our hardware. */
  const uint32_t BAR_LENGTH = 0x200000;
  const uint32_t CTRL_REGS  =  0x80000;
  const uint32_t CTRL_LEN   =     0x30;

  int i, fd;
  uint32_t *ptr;

  fd = open("/sys/bus/pci/devices/0000:00:01.0/resource1", O_RDWR);
  ptr = (uint32_t*) mmap(NULL, BAR_LENGTH, PROT_READ|PROT_WRITE,
			 MAP_SHARED, fd, 0);
  // If ptr == -1, then the user was probably not root
  assert(ptr != MAP_FAILED);

  printf ("Mapped %p bytes beginning at address %p\n", BAR_LENGTH, ptr);

  for (i = CTRL_REGS; i < (CTRL_REGS + CTRL_LEN); i += 4)
    printf ("mmap[0x%08x] (%p) = 0x%08x [0x%08x]\n",
	    i, ptr + i/4, *(ptr + i/4), bswap_32(*(ptr + i/4)));

  munmap(ptr, BAR_LENGTH);
  close(fd);
}