mirror of
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Mark D. Studebaker
13057dbd1d
git-svn-id: http://lm-sensors.org/svn/lm-sensors/trunk@1550 7894878c-1315-0410-8ee3-d5d059ff63e0
100 lines
4.2 KiB
Plaintext
100 lines
4.2 KiB
Plaintext
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**** WARNING: IBM Thinkpad users should not install lm_sensors! ****
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The eeprom of some IBM Thinkpads have been corrupted after installing
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lm_sensors.
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In our releases through 2.6.4, sensors-detect (our userspace detection script)
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corrupts the Atmel 24RF08 eeprom. We have verified this in testing.
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After the eeprom is corrupted, the checksum verification in the BIOS
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will fail and the Thinkpad will not boot.
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The 24RF08 is an 8K eeprom appearing at addresses 0x54 - 0x57 with
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an additional "access protection page" at address 0x5c.
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This is an unusual eeprom that contains a RFID (Radio Frequency ID)
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port for wireless access, and elaborate access protection mechanisms.
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The 24RF08 gets confused (presumably due to a state machine flaw) by
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'quick write 0' (*) probes our package uses for detection.
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This is in violation of the I2C specification. This corruption
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mechanism has never been reported to us on any other eeprom,
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Atmel or otherwise.
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We have made several changes in release 2.6.5 to minimize the
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chance of corruption:
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1) Sensors-detect now accesses DMI information in the BIOS to identify
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the system manufacturer. If the system manufacturer is IBM,
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sensors-detect will print a message and exit.
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2) The sequence of probes in sensors-detect has been changed so that
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24RF08 eeproms are not corrupted. This *should* prevent corruption
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of 24RF08 eeproms in any non-IBM systems in most cases.
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3) The i2c-piix4 module (the bus driver that is used for Intel PIIX4-based
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systems, including IBM Thinkpads) now accesses DMI information
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in the BIOS to identify the system manufacturer. If the system
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manufacturer is IBM, i2c-piix4 will print a message and exit.
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As the 24RF08 is on the PIIX4 SMBus, this prevents access to
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the 24RF08, even if sensors-detect is bypassed or sensors-detect
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does not recognize the system as IBM.
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4) The sequence of probes in the eeprom module (when loaded with
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checksum=1) has been changed so that 24RF08 eeproms will
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not be corrupted. This *should* prevent corruption of 24RF08
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eeproms in non-IBM systems.
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We do not have any reports of this corruption mechanism in releases
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2.6.4 or earlier but have verified that it can happen.
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There is no issue unless the eeprom
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module is loaded with checksum=1, which is not the default.
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Even with these changes, we still DO NOT RECOMMEND INSTALLING
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lm_sensors 2.6.5 on IBM Thinkpads, because:
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1) While these changes will dramatically reduce the chance of 24RF08
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corruption, these changes have not been heavily tested.
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2) lm_sensors won't run on IBM systems because of these changes.
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3) IBM Thinkpads contain a proprietary Embedded Controller which
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is used to access sensors. This controller is not on the SMBus,
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and IBM will not release the programming interface to the
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controller. So lm_sensors isn't useful on Thinkpads anyway.
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As described above, our 2.6.5 release "blacklists" all IBM systems.
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Our next step is to refine the system detection so that only
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those models containing 24RF08's are blacklisted. We are working
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with IBM on a method of querying the MTM (Machine Type and Model)
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and comparing the MTM with a list of 24RF08-containing systems.
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After this change (which will be documented in our CHANGES file
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and this document), users of IBM systems without the
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24RF08 and the proprietary Embedded Controller should be
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able to safely use lm_sensors.
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We do not have any reports of 24RF08 eeproms on non-IBM systems.
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If there are any such systems with 24RF08 eeproms, these changes will
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reduce the chances of corruption. However, there are
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theoretical scenarios (involving multiple bus masters,
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SMP systems, or simultaneous bus access) in which 24RF08's could
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still be corrupted. If you know of any non-IBM systems which contain
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these eeproms, please contact us.
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Thanks to IBM, the Linux Thinkpad Mailing List, and Joe in Australia
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for their assistance on this issue.
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For more information, see:
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The Linux Thinkpad Mailing List
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http://www.bm-soft.com/~bm/tp_mailing.html
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Joe in Australia's Thinkpad Password Recovery Site
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http://www.ja.olm.net/unlock
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Atmel 24RF08 Datasheet
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http://www.atmel.com/atmel/products/prod227.htm
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(*) 'Write Quick 0' is not an actual write and should never generate
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a write operation to an eeprom location.
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