Re: Special handling of sysfs device resource files?

[Ian Romanick <idr@us.ibm.com>]

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Ian Romanick wrote:
> I'm in the process of modifying X to be civilized in it's handling of
> PCI devices on Linux.  As part of that, I've modified it to map the
> /sys/bus/pci/device/*/resource[0-6] files instead of mucking about with
> /dev/mem.
> 
> This seems to mostly work, but I am having one problem.  I map the
> region by opening the file with O_RDWR, then mmap with
> (PROT_READ|PROT_WRITE) and MAP_SHARED.  In all cases, the open and mmap
> succeed.  However, for I/O BARs, the resulting pointer from mmap is
> invalid.  Any access to it results in a segfault and GDB says it's "out
> of range".

I was a little mistaken about this.  The BAR that causes the problem is
not I/O.  It *is* memory.

01:00.0 VGA compatible controller: Matrox Graphics, Inc. G400/G450 (rev
03) (prog-if 00 [VGA])
        Subsystem: Matrox Graphics, Inc. Millennium G400 16Mb SGRAM
        Flags: bus master, medium devsel, latency 64, IRQ 11
        Memory at cc000000 (32-bit, prefetchable) [size=32M]
        Memory at cfefc000 (32-bit, non-prefetchable) [size=16K]
        Memory at cf000000 (32-bit, non-prefetchable) [size=8M]
        Expansion ROM at cfee0000 [disabled] [size=64K]

When I open and mmap resource0 (the framebuffer) I get 0x2b9aa48ea000.
When I open and mmap resource1 (the card's registers) I get
0x2b9aa68ea000.  I can access the resource0 pointer all day long without
problems.  The firs access to the resource1 pointer results in a segfault.

> The base address of the BAR is page aligned, so its not a problem with
> the alignment of mmap vs. the alignment of the BAR.  What else could it
> be?  I'm pretty stumped.
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