diff options
Diffstat (limited to 'Documentation/power')
| -rw-r--r-- | Documentation/power/devices.txt | 90 | ||||
| -rw-r--r-- | Documentation/power/swsusp.txt | 37 |
2 files changed, 23 insertions, 104 deletions
diff --git a/Documentation/power/devices.txt b/Documentation/power/devices.txt index f987afe43e28..fba1e05c47c7 100644 --- a/Documentation/power/devices.txt +++ b/Documentation/power/devices.txt @@ -135,96 +135,6 @@ HW. FREEZE -- stop DMA and interrupts, and be prepared to reinit HW from scratch. That probably means stop accepting upstream requests, the -actual policy of what to do with them beeing specific to a given -driver. It's acceptable for a network driver to just drop packets -while a block driver is expected to block the queue so no request is -lost. (Use IDE as an example on how to do that). FREEZE requires no -power state change, and it's expected for drivers to be able to -quickly transition back to operating state. - -SUSPEND -- like FREEZE, but also put hardware into low-power state. If -there's need to distinguish several levels of sleep, additional flag -is probably best way to do that. - -Transitions are only from a resumed state to a suspended state, never -between 2 suspended states. (ON -> FREEZE or ON -> SUSPEND can happen, -FREEZE -> SUSPEND or SUSPEND -> FREEZE can not). - -All events are: - -[NOTE NOTE NOTE: If you are driver author, you should not care; you -should only look at event, and ignore flags.] - -#Prepare for suspend -- userland is still running but we are going to -#enter suspend state. This gives drivers chance to load firmware from -#disk and store it in memory, or do other activities taht require -#operating userland, ability to kmalloc GFP_KERNEL, etc... All of these -#are forbiden once the suspend dance is started.. event = ON, flags = -#PREPARE_TO_SUSPEND - -Apm standby -- prepare for APM event. Quiesce devices to make life -easier for APM BIOS. event = FREEZE, flags = APM_STANDBY - -Apm suspend -- same as APM_STANDBY, but it we should probably avoid -spinning down disks. event = FREEZE, flags = APM_SUSPEND - -System halt, reboot -- quiesce devices to make life easier for BIOS. event -= FREEZE, flags = SYSTEM_HALT or SYSTEM_REBOOT - -System shutdown -- at least disks need to be spun down, or data may be -lost. Quiesce devices, just to make life easier for BIOS. event = -FREEZE, flags = SYSTEM_SHUTDOWN - -Kexec -- turn off DMAs and put hardware into some state where new -kernel can take over. event = FREEZE, flags = KEXEC - -Powerdown at end of swsusp -- very similar to SYSTEM_SHUTDOWN, except wake -may need to be enabled on some devices. This actually has at least 3 -subtypes, system can reboot, enter S4 and enter S5 at the end of -swsusp. event = FREEZE, flags = SWSUSP and one of SYSTEM_REBOOT, -SYSTEM_SHUTDOWN, SYSTEM_S4 - -Suspend to ram -- put devices into low power state. event = SUSPEND, -flags = SUSPEND_TO_RAM - -Freeze for swsusp snapshot -- stop DMA and interrupts. No need to put -devices into low power mode, but you must be able to reinitialize -device from scratch in resume method. This has two flavors, its done -once on suspending kernel, once on resuming kernel. event = FREEZE, -flags = DURING_SUSPEND or DURING_RESUME - -Device detach requested from /sys -- deinitialize device; proably same as -SYSTEM_SHUTDOWN, I do not understand this one too much. probably event -= FREEZE, flags = DEV_DETACH. - -#These are not really events sent: -# -#System fully on -- device is working normally; this is probably never -#passed to suspend() method... event = ON, flags = 0 -# -#Ready after resume -- userland is now running, again. Time to free any -#memory you ate during prepare to suspend... event = ON, flags = -#READY_AFTER_RESUME -# - - -pm_message_t meaning - -pm_message_t has two fields. event ("major"), and flags. If driver -does not know event code, it aborts the request, returning error. Some -drivers may need to deal with special cases based on the actual type -of suspend operation being done at the system level. This is why -there are flags. - -Event codes are: - -ON -- no need to do anything except special cases like broken -HW. - -# NOTIFICATION -- pretty much same as ON? - -FREEZE -- stop DMA and interrupts, and be prepared to reinit HW from -scratch. That probably means stop accepting upstream requests, the actual policy of what to do with them being specific to a given driver. It's acceptable for a network driver to just drop packets while a block driver is expected to block the queue so no request is diff --git a/Documentation/power/swsusp.txt b/Documentation/power/swsusp.txt index d7814a113ee1..516c5019013b 100644 --- a/Documentation/power/swsusp.txt +++ b/Documentation/power/swsusp.txt @@ -18,10 +18,11 @@ Some warnings, first. * * (*) suspend/resume support is needed to make it safe. * - * If you have any filesystems on USB devices mounted before suspend, + * If you have any filesystems on USB devices mounted before software suspend, * they won't be accessible after resume and you may lose data, as though - * you have unplugged the USB devices with mounted filesystems on them - * (see the FAQ below for details). + * you have unplugged the USB devices with mounted filesystems on them; + * see the FAQ below for details. (This is not true for more traditional + * power states like "standby", which normally don't turn USB off.) You need to append resume=/dev/your_swap_partition to kernel command line. Then you suspend by @@ -204,7 +205,7 @@ Q: There don't seem to be any generally useful behavioral distinctions between SUSPEND and FREEZE. A: Doing SUSPEND when you are asked to do FREEZE is always correct, -but it may be unneccessarily slow. If you want USB to stay simple, +but it may be unneccessarily slow. If you want your driver to stay simple, slowness may not matter to you. It can always be fixed later. For devices like disk it does matter, you do not want to spindown for @@ -357,17 +358,25 @@ Q: Is this true that if I have a mounted filesystem on a USB device and I suspend to disk, I can lose data unless the filesystem has been mounted with "sync"? -A: That's right. It depends on your hardware, and it could be true even for -suspend-to-RAM. In fact, even with "-o sync" you can lose data if your -programs have information in buffers they haven't written out to disk. +A: That's right ... if you disconnect that device, you may lose data. +In fact, even with "-o sync" you can lose data if your programs have +information in buffers they haven't written out to a disk you disconnect, +or if you disconnect before the device finished saving data you wrote. -If you're lucky, your hardware will support low-power modes for USB -controllers while the system is asleep. Lots of hardware doesn't, -however. Shutting off the power to a USB controller is equivalent to -unplugging all the attached devices. +Software suspend normally powers down USB controllers, which is equivalent +to disconnecting all USB devices attached to your system. + +Your system might well support low-power modes for its USB controllers +while the system is asleep, maintaining the connection, using true sleep +modes like "suspend-to-RAM" or "standby". (Don't write "disk" to the +/sys/power/state file; write "standby" or "mem".) We've not seen any +hardware that can use these modes through software suspend, although in +theory some systems might support "platform" or "firmware" modes that +won't break the USB connections. Remember that it's always a bad idea to unplug a disk drive containing a -mounted filesystem. With USB that's true even when your system is asleep! -The safest thing is to unmount all USB-based filesystems before suspending -and remount them after resuming. +mounted filesystem. That's true even when your system is asleep! The +safest thing is to unmount all filesystems on removable media (such USB, +Firewire, CompactFlash, MMC, external SATA, or even IDE hotplug bays) +before suspending; then remount them after resuming. |