Merge branch 'for-linville' of git://github.com/kvalo/ath

[mirror_ubuntu-jammy-kernel.git] / Documentation / fmc / fmc-write-eeprom.txt

fmc-write-eeprom
================

This module is designed to load a binary file from /lib/firmware and to
write it to the internal EEPROM of the mezzanine card. This driver uses
the `busid' generic parameter.

Overwriting the EEPROM is not something you should do daily, and it is
expected to only happen during manufacturing. For this reason, the
module makes it unlikely for the random user to change a working EEPROM.

The module takes the following measures:

   * It accepts a `file=' argument (within /lib/firmware) and if no
     such argument is received, it doesn't write anything to EEPROM
     (i.e. there is no default file name).

   * If the file name ends with `.bin' it is written verbatim starting
     at offset 0.

   * If the file name ends with `.tlv' it is interpreted as
     type-length-value (i.e., it allows writev(2)-like operation).

   * If the file name doesn't match any of the patterns above, it is
     ignored and no write is performed.

   * Only cards listed with `busid=' are written to. If no busid is
     specified, no programming is done (and the probe function of the
     driver will fail).


Each TLV tuple is formatted in this way: the header is 5 bytes,
followed by data. The first byte is `w' for write, the next two bytes
represent the address, in little-endian byte order, and the next two
represent the data length, in little-endian order. The length does not
include the header (it is the actual number of bytes to be written).

This is a real example: that writes 5 bytes at position 0x110:

        spusa.root# od -t x1 -Ax /lib/firmware/try.tlv
        000000 77 10 01 05 00 30 31 32 33 34
        00000a
        spusa.root# insmod /tmp/fmc-write-eeprom.ko busid=0x0200 file=try.tlv
        [19983.391498] spec 0000:03:00.0: write 5 bytes at 0x0110
        [19983.414615] spec 0000:03:00.0: write_eeprom: success

Please note that you'll most likely want to use SDBFS to build your
EEPROM image, at least if your mezzanines are being used in the White
Rabbit environment. For this reason the TLV format is not expected to
be used much and is not expected to be developed further.

If you want to try reflashing fake EEPROM devices, you can use the
fmc-fakedev.ko module (see *note fmc-fakedev::).  Whenever you change
the image starting at offset 0, it will deregister and register again
after two seconds.  Please note, however, that if fmc-write-eeprom is
still loaded, the system will associate it to the new device, which
will be reprogrammed and thus will be unloaded after two seconds.  The
following example removes the module after it reflashed fakedev the
first time.

     spusa.root# insmod fmc-fakedev.ko
        [   72.984733]  fake-fmc: Manufacturer: fake-vendor
        [   72.989434]  fake-fmc: Product name: fake-design-for-testing
        spusa.root# insmod fmc-write-eeprom.ko busid=0 file=fdelay-eeprom.bin; \
            rmmod fmc-write-eeprom
        [  130.874098]  fake-fmc: Matching a generic driver (no ID)
        [  130.887845]  fake-fmc: programming 6155 bytes
        [  130.894567]  fake-fmc: write_eeprom: success
        [  132.895794]  fake-fmc: Manufacturer: CERN
        [  132.899872]  fake-fmc: Product name: FmcDelay1ns4cha


Writing to the EEPROM
=====================

Once you have created a binary file for your EEPROM, you can write it
to the storage medium using the fmc-write-eeprom (See *note
fmc-write-eeprom::, while relying on a carrier driver.  The procedure
here shown here uses the SPEC driver
(`http://www.ohwr.org/projects/spec-sw').

The example assumes no driver is already loaded (actually, I unloaded
them by hand as everything loads automatically at boot time after you
installed the modules), and shows kernel messages together with
commands. Here the prompt is spusa.root# and two SPEC cards are plugged
in the system.

     spusa.root# insmod fmc.ko
     spusa.root# insmod spec.ko
     [13972.382818] spec 0000:02:00.0:  probe for device 0002:0000
     [13972.392773] spec 0000:02:00.0: got file "fmc/spec-init.bin", 1484404 (0x16a674) bytes
     [13972.591388] spec 0000:02:00.0: FPGA programming successful
     [13972.883011] spec 0000:02:00.0: EEPROM has no FRU information
     [13972.888719] spec 0000:02:00.0: No device_id filled, using index
     [13972.894676] spec 0000:02:00.0: No mezzanine_name found
     [13972.899863] /home/rubini/wip/spec-sw/kernel/spec-gpio.c - spec_gpio_init
     [13972.906578] spec 0000:04:00.0:  probe for device 0004:0000
     [13972.916509] spec 0000:04:00.0: got file "fmc/spec-init.bin", 1484404 (0x16a674) bytes
     [13973.115096] spec 0000:04:00.0: FPGA programming successful
     [13973.401798] spec 0000:04:00.0: EEPROM has no FRU information
     [13973.407474] spec 0000:04:00.0: No device_id filled, using index
     [13973.413417] spec 0000:04:00.0: No mezzanine_name found
     [13973.418600] /home/rubini/wip/spec-sw/kernel/spec-gpio.c - spec_gpio_init
     spusa.root# ls /sys/bus/fmc/devices
     fmc-0000  fmc-0001
     spusa.root# insmod fmc-write-eeprom.ko busid=0x0200 file=fdelay-eeprom.bin
     [14103.966259] spec 0000:02:00.0: Matching an generic driver (no ID)
     [14103.975519] spec 0000:02:00.0: programming 6155 bytes
     [14126.373762] spec 0000:02:00.0: write_eeprom: success
     [14126.378770] spec 0000:04:00.0: Matching an generic driver (no ID)
     [14126.384903] spec 0000:04:00.0: fmc_write_eeprom: no filename given: not programming
     [14126.392600] fmc_write_eeprom: probe of fmc-0001 failed with error -2

Reading back the EEPROM
=======================

In order to read back the binary content of the EEPROM of your
mezzanine device, the bus creates a read-only sysfs file called eeprom
for each mezzanine it knows about:

   spusa.root# cd /sys/bus/fmc/devices; ls -l */eeprom
   -r--r--r-- 1 root root 8192 Apr  9 16:53 FmcDelay1ns4cha-f001/eeprom
   -r--r--r-- 1 root root 8192 Apr  9 17:19 fake-design-for-testing-f002/eeprom
   -r--r--r-- 1 root root 8192 Apr  9 17:19 fake-design-for-testing-f003/eeprom
   -r--r--r-- 1 root root 8192 Apr  9 17:19 fmc-f004/eeprom