PCICONFIG_READ(2) Linux Programmer's Manual PCICONFIG_READ(2)

pciconfig_read, pciconfig_write, pciconfig_iobase - pci device information handling

#include <pci.h>
int pciconfig_read(unsigned long bus, unsigned long dfn,
                   unsigned long off, unsigned long len,
                   unsigned char *buf);
int pciconfig_write(unsigned long bus, unsigned long dfn,
                   unsigned long off, unsigned long len,
                   unsigned char *buf);
int pciconfig_iobase(int which, unsigned long bus,
                   unsigned long devfn);

Most of the interaction with PCI devices is already handled by the kernel PCI layer, and thus these calls should not normally need to be accessed from user space.
pciconfig_read()
Reads to buf from device dev at offset off value.
pciconfig_write()
Writes from buf to device dev at offset off value.
pciconfig_iobase()
You pass it a bus/devfn pair and get a physical address for either the memory offset (for things like prep, this is 0xc0000000), the IO base for PIO cycles, or the ISA holes if any.

pciconfig_read()
On success, zero is returned. On error, -1 is returned and errno is set to indicate the error.
pciconfig_write()
On success, zero is returned. On error, -1 is returned and errno is set to indicate the error.
pciconfig_iobase()
Returns information on locations of various I/O regions in physical memory according to the which value. Values for which are: IOBASE_BRIDGE_NUMBER, IOBASE_MEMORY, IOBASE_IO, IOBASE_ISA_IO, IOBASE_ISA_MEM.

EINVAL
len value is invalid. This does not apply to pciconfig_iobase().
EIO
I/O error.
ENODEV
For pciconfig_iobase(), "hose" value is NULL. For the other calls, could not find a slot.
ENOSYS
The system has not implemented these calls (CONFIG_PCI not defined).
EOPNOTSUPP
This return value is valid only for pciconfig_iobase(). It is returned if the value for which is invalid.
EPERM
User does not have the CAP_SYS_ADMIN capability. This does not apply to pciconfig_iobase().

These calls are Linux-specific, available since Linux 2.0.26/2.1.11.

capabilities(7)

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2021-03-22 Linux