On a Linux system, you might be trying to use a utility like decode-dimms to read the SPD EEPROM of your system’s RAM DIMM modules.
But it does not work, and checking the kernel messages, you see:
[ 1.457863] i801_smbus 0000:00:1f.3: enabling device (0001 -> 0003) [ 1.457945] ACPI Warning: SystemIO range 0x0000000000000400-0x000000000000041F conflicts with OpRegion 0x0000000000000400-0x000000000000040F (\SMRG) (20160831/utaddress-247) [ 1.458063] ACPI: If an ACPI driver is available for this device, you should use it instead of the native driver
In this case, the Intel 82801 SMBus driver is attempting to load, finding that the ACPI SMRG (System Management Region) has already claimed part or all of the SMBus I/O range, and failing due to strict ACPI resource enforcement. (In the general case, this will be true of whatever driver is attempting enablement immediately preceding the ACPI messages.)
To work around this and accept the risk of system instability, add the acpi_enforce_resources=lax parameter to your kernel command line and reboot.
Afterwards you will see two extra lines in the output:
[ 1.457863] i801_smbus 0000:00:1f.3: enabling device (0001 -> 0003) [ 1.457945] ACPI Warning: SystemIO range 0x0000000000000400-0x000000000000041F conflicts with OpRegion 0x0000000000000400-0x000000000000040F (\SMRG) (20160831/utaddress-247) [ 1.458031] ACPI: This conflict may cause random problems and system instability [ 1.458063] ACPI: If an ACPI driver is available for this device, you should use it instead of the native driver [ 1.458110] i801_smbus 0000:00:1f.3: SMBus using PCI interrupt
The third line is new and appears advisory, but it is actually advising that the device is being enabled despite the risk of instability posed by two kernel drivers owning the same I/O region. The fifth line is from the driver that was attempting to load and its appearance means that it has proceeded to load.
While this parameter might bypass SMBus conflicts in particular, allowing a utility like decode-dimms to offer functionality not offered by the ACPI BIOS that first claimed that I/O region, it will also bypass this conflict for any device affected by ownership by the ACPI BIOS that would prevent a driver from loading.