Linux Kernel Architecture

Chapter 6: Device Drivers

parent

sibling

parentchild

parent

sibling

child

parent

71: *(*(struc...->parent

name = 0xc11e7300 "PCI Bus #01"start = 4094689280

end = 4095737855flags = 512

parent = sibling = 0xc02f12340xc11e645c

child = 0xc11e345c

57: *(*(struc....sibling

name = 0xc11e661c "Intel Corp. 82815 CGC [Chipset Graphics Controller]"start = 4160749568

end = 4227858431flags = 4616

parent = sibling = 0xc02f12340xc0002120

child = 0x0

60: *(*(struc...8].child

name = start = 40946892800xc11e361c "Intel Corp. 82820 (ICH2) Chipset Ethernet Controller"

end = 4094693375flags = 512

parent = sibling = 0xc11e693c0xc11e485c

child = 0xc11fad60

68: *(*(struc...>sibling

name = 0xc11e4a1c "PCI device 104c:8021 (Texas Instruments)"start = 4094693376

end = 4094695423flags = 512

parent = 0xc11e693csibling = 0xc11e4c5c

child = 0x0

69: *(*(struc...d->child

name = 0xc02c60af "eepro100"start = 4094689280

end = 4094693375flags = 2147483648

parent = sibling = 0x00xc11e345c

child = 0x0

58: *(*(struc...].parent

name = 0xc02aa2a7 "PCI mem"start = 0

end = 4294967295flags = 512

parent = 0x0sibling = 0x0

child = 0xc0002000

Figure 6-21: Allocated resources of a PCI network card.

Even after I/O areas have been mapped, it is necessary on some platforms to use

special methods rather than direct pointer de-referencing to access the individual

memory areas. Table 6-3 shows the functions declared to do this on all platforms

(generally in<asm-arch/io.h>). They should always be used by portable drivers

even if they boil down to simple pointer de-referencing on some architectures

because no other steps are needed to communicate with the I/O areas (as on IA-32

systems, for example).

6.6.3 I/O Ports

I/O ports are a popular way of communicating with devices and buses, above all in the IA-32 world. As

with I/O memory, the required region must first be registered before it can be accessed by a driver in

good faith — unfortunately, the processor is again unable to check whether this has been done.

ioport_resourcefromkernel/resource.cacts as the root element of a resource tree. Theioportsfile

in theprocfilesystem reveals the reserved port addresses.

wolfgang@meitner>cat /proc/ioports

0000-001f : dma1

0020-003f : pic1

0040-005f : timer

0060-006f : keyboard

...