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author | Arnd Bergmann <arnd@arndb.de> | 2012-05-11 17:15:31 +0200 |
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committer | Arnd Bergmann <arnd@arndb.de> | 2012-05-11 17:15:31 +0200 |
commit | 93c6d8927fa692faef3d7d945bd4fe84b0185ad4 (patch) | |
tree | 0a971c86114656ec4e39f7789d9faeb70432c36a /Documentation/power/freezing-of-tasks.txt | |
parent | ea01d31a07ae182028d2398380948f5a4ee09953 (diff) | |
parent | 50260924afd4b745bfb6e5f1caee381a1875fc31 (diff) |
Merge branch 'clk/mxs' of git://git.linaro.org/people/shawnguo/linux-2.6 into next/clock
Shawn Guo <shawn.guo@linaro.org> writes:
mxs common clk porting for v3.5. It depends on the following two branches.
[1] git://git.linaro.org/people/mturquette/linux.git clk-next
[2] http://ftp.arm.linux.org.uk/pub/linux/arm/kernel/git-cur/linux-arm.git clkdev
As the mxs device tree conversion will constantly touch clock files,
to save the conflicts, the updated mxs/dt branch coming later will
based on this pull-request.
* 'clk/mxs' of git://git.linaro.org/people/shawnguo/linux-2.6:
ARM: mxs: remove now unused timer_clk argument from mxs_timer_init
ARM: mxs: remove old clock support
ARM: mxs: switch to common clk framework
ARM: mxs: change the lookup name for fec phy clock
ARM: mxs: request clock for timer
clk: mxs: add clock support for imx28
clk: mxs: add clock support for imx23
clk: mxs: add mxs specific clocks
Includes an update to Linux 3.4-rc6
Conflicts:
drivers/clk/Makefile
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Diffstat (limited to 'Documentation/power/freezing-of-tasks.txt')
-rw-r--r-- | Documentation/power/freezing-of-tasks.txt | 37 |
1 files changed, 19 insertions, 18 deletions
diff --git a/Documentation/power/freezing-of-tasks.txt b/Documentation/power/freezing-of-tasks.txt index ec715cd78fb..6ec291ea1c7 100644 --- a/Documentation/power/freezing-of-tasks.txt +++ b/Documentation/power/freezing-of-tasks.txt @@ -9,7 +9,7 @@ architectures). II. How does it work? -There are four per-task flags used for that, PF_NOFREEZE, PF_FROZEN, TIF_FREEZE +There are three per-task flags used for that, PF_NOFREEZE, PF_FROZEN and PF_FREEZER_SKIP (the last one is auxiliary). The tasks that have PF_NOFREEZE unset (all user space processes and some kernel threads) are regarded as 'freezable' and treated in a special way before the system enters a @@ -17,30 +17,31 @@ suspend state as well as before a hibernation image is created (in what follows we only consider hibernation, but the description also applies to suspend). Namely, as the first step of the hibernation procedure the function -freeze_processes() (defined in kernel/power/process.c) is called. It executes -try_to_freeze_tasks() that sets TIF_FREEZE for all of the freezable tasks and -either wakes them up, if they are kernel threads, or sends fake signals to them, -if they are user space processes. A task that has TIF_FREEZE set, should react -to it by calling the function called __refrigerator() (defined in -kernel/freezer.c), which sets the task's PF_FROZEN flag, changes its state -to TASK_UNINTERRUPTIBLE and makes it loop until PF_FROZEN is cleared for it. -Then, we say that the task is 'frozen' and therefore the set of functions -handling this mechanism is referred to as 'the freezer' (these functions are -defined in kernel/power/process.c, kernel/freezer.c & include/linux/freezer.h). -User space processes are generally frozen before kernel threads. +freeze_processes() (defined in kernel/power/process.c) is called. A system-wide +variable system_freezing_cnt (as opposed to a per-task flag) is used to indicate +whether the system is to undergo a freezing operation. And freeze_processes() +sets this variable. After this, it executes try_to_freeze_tasks() that sends a +fake signal to all user space processes, and wakes up all the kernel threads. +All freezable tasks must react to that by calling try_to_freeze(), which +results in a call to __refrigerator() (defined in kernel/freezer.c), which sets +the task's PF_FROZEN flag, changes its state to TASK_UNINTERRUPTIBLE and makes +it loop until PF_FROZEN is cleared for it. Then, we say that the task is +'frozen' and therefore the set of functions handling this mechanism is referred +to as 'the freezer' (these functions are defined in kernel/power/process.c, +kernel/freezer.c & include/linux/freezer.h). User space processes are generally +frozen before kernel threads. __refrigerator() must not be called directly. Instead, use the try_to_freeze() function (defined in include/linux/freezer.h), that checks -the task's TIF_FREEZE flag and makes the task enter __refrigerator() if the -flag is set. +if the task is to be frozen and makes the task enter __refrigerator(). For user space processes try_to_freeze() is called automatically from the signal-handling code, but the freezable kernel threads need to call it explicitly in suitable places or use the wait_event_freezable() or wait_event_freezable_timeout() macros (defined in include/linux/freezer.h) -that combine interruptible sleep with checking if TIF_FREEZE is set and calling -try_to_freeze(). The main loop of a freezable kernel thread may look like the -following one: +that combine interruptible sleep with checking if the task is to be frozen and +calling try_to_freeze(). The main loop of a freezable kernel thread may look +like the following one: set_freezable(); do { @@ -53,7 +54,7 @@ following one: (from drivers/usb/core/hub.c::hub_thread()). If a freezable kernel thread fails to call try_to_freeze() after the freezer has -set TIF_FREEZE for it, the freezing of tasks will fail and the entire +initiated a freezing operation, the freezing of tasks will fail and the entire hibernation operation will be cancelled. For this reason, freezable kernel threads must call try_to_freeze() somewhere or use one of the wait_event_freezable() and wait_event_freezable_timeout() macros. |