Memory mapping PCI memory region to user space

Phil Nitschke philn at
Mon Mar 27 19:02:22 EST 2006

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)
	Region 1: Memory at 000000009fc00000 (32-bit, non-prefetchable)

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.)


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