Documentation/fmc/fmc-write-eeprom.txt

   1 fmc-write-eeprom
   2 ================
   3
   4 This module is designed to load a binary file from /lib/firmware and to
   5 write it to the internal EEPROM of the mezzanine card. This driver uses
   6 the `busid' generic parameter.
   7
   8 Overwriting the EEPROM is not something you should do daily, and it is
   9 expected to only happen during manufacturing. For this reason, the
  10 module makes it unlikely for the random user to change a working EEPROM.
  11
  12 However, since the EEPROM may include application-specific information
  13 other than the identification, later versions of this packages added
  14 write-support through sysfs. See *note Accessing the EEPROM::.
  15
  16 To avoid damaging the EEPROM content, the module takes the following
  17 measures:
  18
  19    * It accepts a `file=' argument (within /lib/firmware) and if no
  20      such argument is received, it doesn't write anything to EEPROM
  21      (i.e. there is no default file name).
  22
  23    * If the file name ends with `.bin' it is written verbatim starting
  24      at offset 0.
  25
  26    * If the file name ends with `.tlv' it is interpreted as
  27      type-length-value (i.e., it allows writev(2)-like operation).
  28
  29    * If the file name doesn't match any of the patterns above, it is
  30      ignored and no write is performed.
  31
  32    * Only cards listed with `busid=' are written to. If no busid is
  33      specified, no programming is done (and the probe function of the
  34      driver will fail).
  35
  36
  37 Each TLV tuple is formatted in this way: the header is 5 bytes,
  38 followed by data. The first byte is `w' for write, the next two bytes
  39 represent the address, in little-endian byte order, and the next two
  40 represent the data length, in little-endian order. The length does not
  41 include the header (it is the actual number of bytes to be written).
  42
  43 This is a real example: that writes 5 bytes at position 0x110:
  44
  45         spusa.root# od -t x1 -Ax /lib/firmware/try.tlv
  46         000000 77 10 01 05 00 30 31 32 33 34
  47         00000a
  48         spusa.root# insmod /tmp/fmc-write-eeprom.ko busid=0x0200 file=try.tlv
  49         [19983.391498] spec 0000:03:00.0: write 5 bytes at 0x0110
  50         [19983.414615] spec 0000:03:00.0: write_eeprom: success
  51
  52 Please note that you'll most likely want to use SDBFS to build your
  53 EEPROM image, at least if your mezzanines are being used in the White
  54 Rabbit environment. For this reason the TLV format is not expected to
  55 be used much and is not expected to be developed further.
  56
  57 If you want to try reflashing fake EEPROM devices, you can use the
  58 fmc-fakedev.ko module (see *note fmc-fakedev::).  Whenever you change
  59 the image starting at offset 0, it will deregister and register again
  60 after two seconds.  Please note, however, that if fmc-write-eeprom is
  61 still loaded, the system will associate it to the new device, which
  62 will be reprogrammed and thus will be unloaded after two seconds.  The
  63 following example removes the module after it reflashed fakedev the
  64 first time.
  65
  66      spusa.root# insmod fmc-fakedev.ko
  67         [   72.984733]  fake-fmc: Manufacturer: fake-vendor
  68         [   72.989434]  fake-fmc: Product name: fake-design-for-testing
  69         spusa.root# insmod fmc-write-eeprom.ko busid=0 file=fdelay-eeprom.bin; \
  70             rmmod fmc-write-eeprom
  71         [  130.874098]  fake-fmc: Matching a generic driver (no ID)
  72         [  130.887845]  fake-fmc: programming 6155 bytes
  73         [  130.894567]  fake-fmc: write_eeprom: success
  74         [  132.895794]  fake-fmc: Manufacturer: CERN
  75         [  132.899872]  fake-fmc: Product name: FmcDelay1ns4cha
  76
  77
  78 Accessing the EEPROM
  79 =====================
  80
  81 The bus creates a sysfs binary file called eeprom for each mezzanine it
  82 knows about:
  83
  84         spusa.root# cd /sys/bus/fmc/devices; ls -l */eeprom
  85         -r--r--r-- 1 root root 8192 Feb 21 12:30 FmcAdc100m14b4cha-0800/eeprom
  86         -r--r--r-- 1 root root 8192 Feb 21 12:30 FmcDelay1ns4cha-0200/eeprom
  87         -r--r--r-- 1 root root 8192 Feb 21 12:30 FmcDio5cha-0400/eeprom
  88
  89 Everybody can read the files and the superuser can also modify it, but
  90 the operation may on the carrier driver, if the carrier is unable to
  91 access the I2C bus.  For example, the spec driver can access the bus
  92 only with its golden gateware: after a mezzanine driver reprogrammed
  93 the FPGA with a custom circuit, the carrier is unable to access the
  94 EEPROM and returns ENOTSUPP.
  95
  96 An alternative way to write the EEPROM is the mezzanine driver
  97 fmc-write-eeprom (See *note fmc-write-eeprom::), but the procedure is
  98 more complex.