Merge branch 'soc-core' of...

What:		/sys/bus/hsi

Date:		April 2012

KernelVersion:	3.4

Contact:	Carlos Chinea <carlos.chinea@nokia.com>

Description:

		High Speed Synchronous Serial Interface (HSI) is a

		serial interface mainly used for connecting application

		engines (APE) with cellular modem engines (CMT) in cellular

		handsets.

		The bus will be populated with devices (hsi_clients) representing

		the protocols available in the system. Bus drivers implement

		those protocols.

What:		/sys/bus/hsi/devices/.../modalias

Date:		April 2012

KernelVersion:	3.4

Contact:	Carlos Chinea <carlos.chinea@nokia.com>

Description:	Stores the same MODALIAS value emitted by uevent

		Format: hsi:<hsi_client device name>

* Calxeda SATA Controller

* AHCI SATA Controller

SATA nodes are defined to describe on-chip Serial ATA controllers.

Each SATA controller should have its own node.

Required properties:

- compatible        : compatible list, contains "calxeda,hb-ahci"

- compatible        : compatible list, contains "calxeda,hb-ahci" or "snps,spear-ahci"

- interrupts        : <interrupt mapping for SATA IRQ>

- reg               : <registers mapping>

                reg = <0xffe08000 0x1000>;

                interrupts = <115>;

        };

Required properties:

- compatible : "fsl,sgtl5000".

- reg : the I2C address of the device

Example:

codec: sgtl5000@0a {

	(if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),

	if it is <= 0.

	Possible values are [-31, 31], inclusive.

	Default: 2

	Default: 1

tcp_allowed_congestion_control - STRING

	Show/set the congestion control choices available to non-privileged

	net.core.rmem_max.  Calling setsockopt() with SO_RCVBUF disables

	automatic tuning of that socket's receive buffer size, in which

	case this value is ignored.

	Default: between 87380B and 4MB, depending on RAM size.

	Default: between 87380B and 6MB, depending on RAM size.

tcp_sack - BOOLEAN

	Enable select acknowledgments (SACKS).

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

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 {

(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.