+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 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
+#
git://git.onelab.eu / linux-2.6.git / blobdiff