Debian: What are these files in /sys/devices/pci0000:00/ for?

Question

I am running Debian Squeeze on an MSI M670 laptop. I have these following files on my root drive, each 256MB:

file:///sys/devices/pci0000:00/0000:00:05.0/resource1
file:///sys/devices/pci0000:00/0000:00:05.0/resource1_wc

Here is my lspci output:

muhuk@debian:~$ lspci
00:00.0 RAM memory: nVidia Corporation C51 Host Bridge (rev a2)
00:00.2 RAM memory: nVidia Corporation C51 Memory Controller 1 (rev a2)
00:00.3 RAM memory: nVidia Corporation C51 Memory Controller 5 (rev a2)
00:00.4 RAM memory: nVidia Corporation C51 Memory Controller 4 (rev a2)
00:00.5 RAM memory: nVidia Corporation C51 Host Bridge (rev a2)        
00:00.6 RAM memory: nVidia Corporation C51 Memory Controller 3 (rev a2)
00:00.7 RAM memory: nVidia Corporation C51 Memory Controller 2 (rev a2)
00:03.0 PCI bridge: nVidia Corporation C51 PCI Express Bridge (rev a1)
00:05.0 VGA compatible controller: nVidia Corporation C51 [GeForce Go 6100] (rev a2)
00:09.0 RAM memory: nVidia Corporation MCP51 Host Bridge (rev a2)
00:0a.0 ISA bridge: nVidia Corporation MCP51 LPC Bridge (rev a3)
00:0a.1 SMBus: nVidia Corporation MCP51 SMBus (rev a3)
00:0a.3 Co-processor: nVidia Corporation MCP51 PMU (rev a3)
00:0b.0 USB Controller: nVidia Corporation MCP51 USB Controller (rev a3)
00:0b.1 USB Controller: nVidia Corporation MCP51 USB Controller (rev a3)
00:0d.0 IDE interface: nVidia Corporation MCP51 IDE (rev a1)
00:0e.0 IDE interface: nVidia Corporation MCP51 Serial ATA Controller (rev a1)
00:0f.0 IDE interface: nVidia Corporation MCP51 Serial ATA Controller (rev a1)
00:10.0 PCI bridge: nVidia Corporation MCP51 PCI Bridge (rev a2)
00:10.1 Audio device: nVidia Corporation MCP51 High Definition Audio (rev a2)
00:14.0 Bridge: nVidia Corporation MCP51 Ethernet Controller (rev a3)
00:18.0 Host bridge: Advanced Micro Devices [AMD] K8 [Athlon64/Opteron] HyperTransport Technology Configuration
00:18.1 Host bridge: Advanced Micro Devices [AMD] K8 [Athlon64/Opteron] Address Map
00:18.2 Host bridge: Advanced Micro Devices [AMD] K8 [Athlon64/Opteron] DRAM Controller
00:18.3 Host bridge: Advanced Micro Devices [AMD] K8 [Athlon64/Opteron] Miscellaneous Control
04:04.0 FireWire (IEEE 1394): O2 Micro, Inc. Firewire (IEEE 1394) (rev 02)
04:04.2 SD Host controller: O2 Micro, Inc. Integrated MMC/SD Controller (rev 01)
04:04.3 Mass storage controller: O2 Micro, Inc. Integrated MS/xD Controller (rev 01)
04:09.0 Network controller: RaLink RT2561/RT61 rev B 802.11g

I am speculating these have something to do with the shared RAM my GPU is using. But why a file on disk? And why two of them?

Answer 1

It's a file because Linux tries to provide as much low-level access as possible to userspace. It isn't really on disk because all the structures in /sys only exist within the kernel. There's two of them because the second is used for write combining.