Appendix Q. Power Management Support

This release includes support for APM-based power management. This means that our driver will support suspend and resume, but will not support standby.

Your laptop's system BIOS will need to support APM, rather than ACPI. Many, but not all, of the GeForce2- and GeForce4-based laptops include APM support. You can check for APM support via the procfs interface (check for the existence of /proc/apm) or via the kernel's boot output:

    % dmesg | grep -i apm

a message similar to this indicates APM support:

    apm: BIOS version 1.2 Flags 0x03 (Driver version 1.16)

or a message like this indicates no APM support:

    No APM support in Kernel

Although ACPI support is advancing in development kernels and some backported patches for 2.4 kernels exist, the NVIDIA graphics driver does not yet provide support for ACPI. We hope to finish this support in the near future.

Note that standby is not supported, but that the kernel will attempt to enter standby if told to do so. When changing power levels, many system services are alerted of the change so that they can handle the change appropriately. For example, networking will be disabled before suspending, then reenabled when resuming. When the kernel attempts to enter standby, the BIOS will fail the attempt. The kernel will print out the error message "standby: Parameter out of range", but will fail to notify the system services of the failure. As a result, the system will not go into suspension, but all system services will be disabled and the system will appear to be hung. The best way to recover from this situation is to enter suspend, then resume.

Power management support is still under development and is a beta feature. As a result, some functionality is still missing or unreliable. Known problems include:

Sometimes chipsets lose their AGP configuration during suspend, and may cause corruption on the bus upon resume. The AGP driver is required to save and restore relevant register state on such systems; NVIDIA's NvAGP is notified of power management events and ensures its configuration is kept intact across suspend/resume cycles.

Linux 2.4 AGPGART does not support power management, Linux 2.6 AGPGART does, but only for a few select chipsets. If you use either of these two AGP drivers and find your system fails to resume reliably, you may have more success with NVIDIA's NvAGP driver.

Disabling AGP support (please see Appendix F, Configuring AGP for more details on disabling AGP) will also work around this problem.

For ACPI, only S3 "Suspend to Ram" is currently supported. This means that S4 "Suspend to Disk", otherwise known as "Software Suspend" or "swsusp" does not currently work reliably.