Memory mapping PCI memory region to user space

[Kumar Gala]

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?

- kumar