Intel I211 NIC 8086:1539: reading/writing flash works for me

I was able to change MAC address of my NIC.
Required specifying `iomem=relaxed` to kernel cmdline.

$ lspci -vnn
...
08:00.0 Ethernet controller [0200]: Intel Corporation I211 Gigabit
Network Connection [8086:1539] (rev 03)
    Subsystem: Gigabyte Technology Co., Ltd Device [1458:e000]
    Flags: bus master, fast devsel, latency 0, IRQ 39
    Memory at fcb00000 (32-bit, non-prefetchable) [size=128K]
    I/O ports at f000 [size=32]
    Memory at fcb20000 (32-bit, non-prefetchable) [size=16K]
    Capabilities: <access denied>
    Kernel driver in use: igb
    Kernel modules: igb

$ sudo flashrom -pnicintel_eeprom -r 123
flashrom v1.2 on Linux 5.8.18-200.fc32.x86_64 (x86_64)
flashrom is free software, get the source code at https://flashrom.org

Using clock_gettime for delay loops (clk_id: 1, resolution: 1ns).
===
This PCI device is UNTESTED. Please report the 'flashrom -p xxxx'
output
to [e-mail] if it works for you. Please add the name of
your
PCI device to the subject. Thank you for your help!
===
Found Programmer flash chip "Opaque flash chip" (4 kB, Programmer-
specific) on nicintel_eeprom.
Reading flash... done.

Reading is no problem. Writing operation reports 'Flash update failed'
at the end, however changes apply to the flash.

$ sudo flashrom -pnicintel_eeprom -w 123
flashrom v1.2 on Linux 5.8.18-200.fc32.x86_64 (x86_64)
flashrom is free software, get the source code at https://flashrom.org

Using clock_gettime for delay loops (clk_id: 1, resolution: 1ns).
===
This PCI device is UNTESTED. Please report the 'flashrom -p xxxx'
output
to [e-mail] if it works for you. Please add the name of
your
PCI device to the subject. Thank you for your help!
===
Found Programmer flash chip "Opaque flash chip" (4 kB, Programmer-
specific) on nicintel_eeprom.
Reading old flash chip contents... done.
Erasing and writing flash chip... Erase/write done.
Verifying flash... VERIFIED.
Flash update failed