Commit e253c5e3 authored by Larry Finger's avatar Larry Finger Committed by Michael Büsch

Extend README file.
parent 70d21fd8
......@@ -13,3 +13,104 @@ Requirements
------------
1) C99 compatible compiler.
Usage
-----
The contents of the sprom are exposed to the user in sysfs. This
tool can, in principle, read and write the sprom in place; however,
making a mistake during sprom writing could render your device
unusable. For this reason, we recommend copying the sprom contents
to disk as the first step. This copy can then be modified until it
contains the desired new information. Only then and with caution
should the sprom be rewritten. DO NOT MAKE ANY CHANGES UNLESS YOU
KNOW WHAT YOU ARE DOING!!!! You have been warned!!!
Obtaining a disk copy of the sprom contents
-------------------------------------------
This file name for the sprom contents depends on the bus layout of
the specific computer being used and will be something like
/sys/devices/pci0000:00/0000:00:0d.0/0000:04:00.0/ssb_sprom
It is not recommended that you try to type the name. Instead, you
should use the following commands to get and check the path for the
sprom file:
SSB_SPROM=$(find /sys -name ssb_sprom)
echo $SSB_SPROM
If the echo command only results in a single instance of "/sys/...",
you may proceed. For systems with more than one SSB-based interface,
there will be such a string for each, and the command that sets the
SSB_SPROM symbol will have to be changed. In the name above, the
sequence states that this device is attached to the 0'th PCI bus via
bridge 0d.0 and is device 04:00.0 on that bridge. To find which of
your SSB devices to select, use the 'lspci -v' command. On my system,
the first line of such output for my interface is "04:00.0 Network
controller: Broadcom Corporation BCM94311MCG wlan mini-PCI (rev 02)".
To select only this device, one would use
SSB_SPROM=$(find /sys -name ssb_sprom | grep 04:00.0)
echo $SSB_SPROM
Of course, the "04:00.0" needs to match your system, and check the
output value to determine that there is now a single instance of
"/sys..." and that the path matches the device whose SPROM is to be
changed. If not, adjust the string after 'grep' accordingly.
Once the SSB_SPROM variable matches the path to ssb_sprom for your
device, get a working copy of the sprom contents with
sudo cat $SSB_SPROM > ssb_sprom_copy
Modifying the contents of the working copy
------------------------------------------
You may now see the contents of your sprom with the command
ssb-sprom -i ssb_sprom_copy -P
As an example, let us suppose that you have purchased a Dell mini-pci
card to use in an HP laptop. The HP BIOS refuses to use the card when
the pcivendor is Dell (code 0x1028), not HP (code 0x103C). From the
information provided by an "ssb-prom --help" command, we learn that
the switch needed to change this vendor code is "--subv". To change
that code, we use the command
ssb-sprom -i ssb_sprom_copy -o new_ssb_sprom_copy --subv 0x103C
to write the HP vendor ID to our working copy. I use different
input and output files so as not to destroy the original. If further
changes are needed, for example the PCI product ID, the command
ssb-sprom -i new_ssb_sprom_copy -o new_ssb_sprom_copy --subp 0x137C
would be used. Note that the input and output files may be the same.
Once you think you have updated correctly, use
ssb-sprom -i new_ssb_sprom_copy -P
to check the contents.
Rewriting the sprom contents
----------------------------
Once the sprom contents are the way you want them, and presumably
correct, you are ready to rewrite the file. First, use
echo $SSB_SPROM
to ensure that this symbol still contains the SPROM path. If not,
then it will have to be reloaded as discussed above.
You are then ready to rewrite the sprom with
sudo cp new_ssb_sprom_copy $SSB_SPROM
Once again, you are urged to be absolutely certain of the contents
of the working copy BEFORE taking this step. If your interface
becomes unusable as a result of writing incorrect data into the
sprom, the responsibility is YOURS. Once again, you have been warned.
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