[Bug 781] New: LM4857 should be turned off on a reboot notifier

bugzilla-daemon at bugzilla.openmoko.org bugzilla-daemon at bugzilla.openmoko.org
Fri Aug 31 03:06:10 CEST 2007


           Summary: LM4857 should be turned off on a reboot notifier
           Product: OpenMoko
           Version: unspecified
          Platform: Neo1973
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: kernel
        AssignedTo: laforge at openmoko.org
        ReportedBy: cesarb at cesarb.net
                CC: buglog at lists.openmoko.org

According to http://wiki.openmoko.org/wiki/Neo1973_GTA01_Power_Management, the
LM4857 is connected directly to the battery, and its datasheet shows it uses
several mA when not off. If it is not turned off when shutting down, it will
drain the battery even with the phone off. To avoid this, it should be turned
off when rebooting or powering off the phone.

The best place to turn it off would be by the sound driver in the reboot
notifier chain (register_reboot_notifier). As a workaround, you can set the "Amp
Mode" mixer to "Off" (0) before shutting down the phone.

Thanks to SpeedEvil for guessing the LM4857 was not being turned off and for
measuring the currents.

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