This adds a function to the pinctrl core to retrieve the GPIO
range associated with a certain pin for a certain controller.
This is needed when a pinctrl driver want to look up the
corresponding struct gpio_chip for a certain pin. As the
GPIO drivers can now create these ranges themselves, the
pinctrl driver no longer knows about all its associated GPIO
chips.
Reviewed-by: NStephen Warren <swarren@nvidia.com>
Reviewed-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

Rename the function find_pinctrl_and_add_gpio_range()
to pinctrl_find_and_add_gpio_range() so as to be consistent
with the rest of the functions.
Reviewed-by: NStephen Warren <swarren@nvidia.com>
Reviewed-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

The fact that of_gpiochip_add_pin_range() and
gpiochip_add_pin_range() share too much code is fragile and
will invariably mean that bugs need to be fixed in two places
instead of one.

So separate the concerns of gpiolib.c and gpiolib-of.c and
have the latter call the former as back-end. This is necessary
also when going forward with other device descriptions such
as ACPI.

This is done by:

- Adding a return code to gpiochip_add_pin_range() so we can
  reliably check whether this succeeds.

- Get rid of the custom of_pinctrl_add_gpio_range() from
  pinctrl. Instead create of_pinctrl_get() to just retrive the
  pin controller per se from an OF node. This composite
  function was just begging to be deleted, it was way to
  purpose-specific.

- Use pinctrl_dev_get_name() to get the name of the retrieved
  pin controller and use that to call back into the generic
  gpiochip_add_pin_range().

Now the pin range is only allocated and tied to a pin
controller from the core implementation in gpiolib.c.
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

pinctrl subsystem needs gpio chip base to prepare set of gpio
pin ranges, which a given pinctrl driver can handle. This is
important to handle pinctrl gpio request calls in order to
program a given pin properly for gpio operation.

As gpio base is allocated dynamically during gpiochip
registration, presently there exists no clean way to pass this
information to the pinctrl subsystem.

After few discussions from [1], it was concluded that may be
gpio controller reporting the pin range it supports, is a
better way than pinctrl subsystem directly registering it.

[1] http://comments.gmane.org/gmane.linux.ports.arm.kernel/184816

Cc: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NShiraz Hashim <shiraz.hashim@st.com>
[Edited documentation a bit]
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

This reverts earlier commit which removed
pinctrl_remove_gpio_range(), because at that time there
weren't any more users of that routine. It was removed as the
removal of ranges was done in unregister of pinctrl.

But as we are now registering stuff from gpiolib, we may
remove and insert a gpio module multiple times. So, we
need this routine again.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

Convert #include "..." to #include <path/...> in kernel system headers.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NArnd Bergmann <arnd@arndb.de>
Acked-by: NThomas Gleixner <tglx@linutronix.de>
Acked-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: NDave Jones <davej@redhat.com>

Often GPIO ranges are added in batch, so create a special
function for that.
Acked-by: NStephen Warren <swarren@wwwdotorg.org>
Signed-off-by: NDong Aisheng <dong.aisheng@linaro.org>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

The gpio ranges will be automatically removed when the pinctrl
driver is unregistered.
Acked-by: NStephen Warren <swarren@wwwdotorg.org>
Signed-off-by: NDong Aisheng <dong.aisheng@linaro.org>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

Signed-off-by: NStephen Warren <swarren@nvidia.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

Most of the SoC drivers implement list_groups() and list_functions()
routines for pinctrl and pinmux. These routines continue returning
zero until the selector argument is greater than total count of
available groups or functions.

This patch replaces these list_*() routines with get_*_count()
routines, which returns the number of available selection for SoC
driver. pinctrl layer will use this value to check the range it can
choose.

This patch fixes all user drivers for this change. There are other
routines in user drivers, which have checks to check validity of
selector passed to them. It is also no more required and hence
removed.

Documentation updated as well.
Acked-by: NStephen Warren <swarren@wwwdotorg.org>
Signed-off-by: NViresh Kumar <viresh.kumar@st.com>
[Folded in fix and fixed a minor merge artifact manually]
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

During pinctrl_get(), if the client device has a device tree node, look
for the common pinctrl properties there. If found, parse the referenced
device tree nodes, with the help of the pinctrl drivers, and generate
mapping table entries from them.

During pinctrl_put(), free any results of device tree parsing.
Acked-by: NDong Aisheng <dong.aisheng@linaro.org>
Signed-off-by: NStephen Warren <swarren@wwwdotorg.org>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

Add a dummy declaration of struct device to avoid the following warning:

In file included from include/linux/pinctrl/machine.h:15:0,
                 from arch/arm/mach-tegra/board-pinmux.h:18,
                 from arch/arm/mach-tegra/board-trimslice-pinmux.c:20:
include/linux/pinctrl/pinctrl.h:115:12: warning: 'struct device' declared inside parameter list [enabled by default]
include/linux/pinctrl/pinctrl.h:115:12: warning: its scope is only this definition or declaration, which is probably not what you want [enabled by default]
Signed-off-by: NStephen Warren <swarren@wwwdotorg.org>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

Move the pin control state defines into its own header file,
since it is used both by machine.h which is facing the platform
and by consumer.h which is facing the drivers, and pinctrl.h
which is pinctrl-driver internal, let's not have each and every
.h file include all others, then isolation is moot.
Acked-by: NStephen Warren <swarren@wwwdotorg.org>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

There are many problems with the current pinctrl locking:

struct pinctrl_dev's gpio_ranges_lock isn't effective;
pinctrl_match_gpio_range() only holds this lock while searching for a gpio
range, but the found range is return and manipulated after releading the
lock. This could allow pinctrl_remove_gpio_range() for that range while it
is in use, and the caller may very well delete the range after removing it,
causing pinctrl code to touch the now-free range object.

Solving this requires the introduction of a higher-level lock, at least
a lock per pin controller, which both gpio range registration and
pinctrl_get()/put() will acquire.

There is missing locking on HW programming; pin controllers may pack the
configuration for different pins/groups/config options/... into one
register, and hence have to read-modify-write the register. This needs to
be protected, but currently isn't. Related, a future change will add a
"complete" op to the pin controller drivers, the idea being that each
state's programming will be programmed into the pinctrl driver followed
by the "complete" call, which may e.g. flush a register cache to HW. For
this to work, it must not be possible to interleave the pinctrl driver
calls for different devices.

As above, solving this requires the introduction of a higher-level lock,
at least a lock per pin controller, which will be held for the duration
of any pinctrl_enable()/disable() call.

However, each pinctrl mapping table entry may affect a different pin
controller if necessary. Hence, with a per-pin-controller lock, almost
any pinctrl API may need to acquire multiple locks, one per controller.
To avoid deadlock, these would need to be acquired in the same order in
all cases. This is extremely difficult to implement in the case of
pinctrl_get(), which doesn't know which pin controllers to lock until it
has parsed the entire mapping table, since it contains somewhat arbitrary
data.

The simplest solution here is to introduce a single lock that covers all
pin controllers at once. This will be acquired by all pinctrl APIs.

This then makes struct pinctrl's mutex irrelevant, since that single lock
will always be held whenever this mutex is currently held.
Signed-off-by: NStephen Warren <swarren@nvidia.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

This provides a single centralized name for the default state.

Update PIN_MAP_* macros to use this state name, instead of requiring the
user to pass a state name in.

With this change, hog entries in the mapping table are defined as those
with state name PINCTRL_STATE_DEFAULT, i.e. all entries have the same
name. This interacts badly with the nested iteration over mapping table
entries in pinctrl_hog_maps() and pinctrl_hog_map() which would now
attempt to claim each hog mapping table entry multiple times. Replacing
the custom hog code with a simple pinctrl_get()/pinctrl_enable().

Update documentation and mapping tables to use this.
Signed-off-by: NStephen Warren <swarren@nvidia.com>
Acked-by: NDong Aisheng <dong.aisheng@linaro.org>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

This patch removes maxpin member in the pin control descriptor
because we don't need this value as we enumerate a pin space
using offset.
Signed-off-by: NChanho Park <chanho61.park@samsung.com>
Signed-off-by: NKyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

This add per-pin and per-group pin config interfaces for biasing,
driving and other such electronic properties. The details of passed
configurations are passed in an opaque unsigned long which may be
dereferences to integer types, structs or lists on either side
of the configuration interface.

ChangeLog v1->v2:
- Clear split of terminology: we now have pin controllers, and
  those may support two interfaces using vtables: pin
  multiplexing and pin configuration.
- Break out pin configuration to its own C file, controllers may
  implement only config without mux, and vice versa, so keep each
  sub-functionality of pin controllers separate. Introduce
  CONFIG_PINCONF in Kconfig.
- Implement some core logic around pin configuration in the
  pinconf.c file.
- Remove UNKNOWN config states, these were just surplus baggage.
- Remove FLOAT config state - HIGH_IMPEDANCE should be enough for
  everyone.
- PIN_CONFIG_POWER_SOURCE added to handle switching the power
  supply for the pin logic between different sources
- Explicit DISABLE config enums to turn schmitt-trigger,
  wakeup etc OFF.
- Update documentation to reflect all the recent reasoning.
ChangeLog v2->v3:
- Twist API around to pass around arrays of config tuples instead
  of (param, value) pairs everywhere.
- Explicit drive strength semantics for push/pull and similar
  drive modes, this shall be the number of drive stages vs
  nominal load impedance, which should match the actual
  electronics used in push/pull CMOS or TTY totempoles.
- Drop load capacitance configuration - I probably don't know
  what I'm doing here so leave it out.
- Drop PIN_CONFIG_INPUT_SCHMITT_OFF, instead the argument zero to
  PIN_CONFIG_INPUT_SCHMITT turns schmitt trigger off.
- Drop PIN_CONFIG_NORMAL_POWER_MODE and have a well defined
  argument to PIN_CONFIG_LOW_POWER_MODE to get out of it instead.
- Drop PIN_CONFIG_WAKEUP_ENABLE/DISABLE and just use
  PIN_CONFIG_WAKEUP with defined value zero to turn wakeup off.
- Add PIN_CONFIG_INPUT_DEBOUNCE for configuring debounce time
  on input lines.
- Fix a bug when we tried to configure pins for pin controllers
  without pinconf support.
- Initialized debugfs properly so it works.
- Initialize the mutex properly and lock around config tampering
  sections.
- Check the return value from get_initial_config() properly.
ChangeLog v3->v4:
- Export the pin_config_get(), pin_config_set() and
  pin_config_group() functions.
- Drop the entire concept of just getting initial config and
  keeping track of pin states internally, instead ask the pins
  what state they are in. Previous idea was plain wrong, if the
  device cannot keep track of its state, the driver should do
  it.
- Drop the generic configuration layout, it seems this impose
  too much restriction on some pin controllers, so let them do
  things the way they want and split off support for generic
  config as an optional add-on.
ChangeLog v4->v5:
- Introduce two symmetric driver calls for group configuration,
  .pin_config_group_[get|set] and corresponding external calls.
- Remove generic semantic meanings of return values from config
  calls, these belong in the generic config patch. Just pass the
  return value through instead.
- Add a debugfs entry "pinconf-groups" to read status from group
  configuration only, also slam in a per-group debug callback in
  the pinconf_ops so custom drivers can display something
  meaningful for their pins.
- Fix some dangling newline.
- Drop dangling #else clause.
- Update documentation to match the above.
ChangeLog v5->v6:
- Change to using a pin name as parameter for the
  [get|set]_config() functions, as suggested by Stephen Warren.
  This is more natural as names will be what a developer has
  access to in written documentation etc.
ChangeLog v6->v7:
- Refactor out by-pin and by-name get/set functions, only expose
  the by-name functions externally, expose the by-pin functions
  internally.
- Show supported pin control functionality in the debugfs
  pinctrl-devices file.
Acked-by: NStephen Warren <swarren@nvidia.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

This patch enables mapping a base offset of gpio ranges with
a pin offset even if does'nt matched. A base of pinctrl_gpio_range
means a base offset of gpio. However, we cannot convert gpio to pin
number for sparse gpio ranges just only using a gpio base offset.
We can convert a gpio to real pin number(even if not matched) using
a new pin_base which means a base pin offset of requested gpio range.
Now, the pin control subsystem passes the pin base offset to the
pinmux driver.

For example, let's assume below two gpio ranges in the system.

static struct pinctrl_gpio_range gpio_range_a = {
    .name = "chip a",
    .id = 0,
    .base = 32,
    .pin_base = 32,
    .npins = 16,
    .gc = &chip_a;
};

static struct pinctrl_gpio_range gpio_range_b = {
    .name = "chip b",
    .id = 0,
    .base = 48,
    .pin_base = 64,
    .npins = 8,
    .gc = &chip_b;
};

We can calucalate a exact pin ranges even if doesn't matched with gpio ranges.

chip a:
    gpio-range : [32 .. 47]
    pin-range  : [32 .. 47]
chip b:
    gpio-range : [48 .. 55]
    pin-range  : [64 .. 71]
Signed-off-by: NChanho Park <chanho61.park@samsung.com>
Signed-off-by: NKyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

when pinctl subsystem is not selected, when compiling drivers including
the include/linux/pinctrl/pinctrl.h, we will get the warning as below:
In file included from include/linux/pinctrl/pinmux.h:17,
                 from drivers/tty/serial/sirfsoc_uart.c:25:
include/linux/pinctrl/pinctrl.h:126: warning: 'struct pinctrl_dev'
		declared inside parameter list
include/linux/pinctrl/pinctrl.h:126: warning: its scope is only this
      definition or declaration, which is probably not what you want
Signed-off-by: NBarry Song <Baohua.Song@csr.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

get_group_pins() "returns" a pointer to an array of const objects, through
a pointer parameter. Fix the prototype so what's pointed at by the returned
pointer is const, rather than the function parameter being const.

This also allows the removal of a cast in each of the two current pinmux
drivers.
Signed-off-by: NStephen Warren <swarren@nvidia.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

This creates a subsystem for handling of pin control devices.
These are devices that control different aspects of package
pins.

Currently it handles pinmuxing, i.e. assigning electronic
functions to groups of pins on primarily PGA and BGA type of
chip packages which are common in embedded systems.

The plan is to also handle other I/O pin control aspects
such as biasing, driving, input properties such as
schmitt-triggering, load capacitance etc within this
subsystem, to remove a lot of ARM arch code as well as
feature-creepy GPIO drivers which are implementing the same
thing over and over again.

This is being done to depopulate the arch/arm/* directory
of such custom drivers and try to abstract the infrastructure
they all need. See the Documentation/pinctrl.txt file that is
part of this patch for more details.

ChangeLog v1->v2:

- Various minor fixes from Joe's and Stephens review comments
- Added a pinmux_config() that can invoke custom configuration
  with arbitrary data passed in or out to/from the pinmux driver

ChangeLog v2->v3:

- Renamed subsystem folder to "pinctrl" since we will likely
  want to keep other pin control such as biasing in this
  subsystem too, so let us keep to something generic even though
  we're mainly doing pinmux now.
- As a consequence, register pins as an abstract entity separate
  from the pinmux. The muxing functions will claim pins out of the
  pin pool and make sure they do not collide. Pins can now be
  named by the pinctrl core.
- Converted the pin lookup from a static array into a radix tree,
  I agreed with Grant Likely to try to avoid any static allocation
  (which is crap for device tree stuff) so I just rewrote this
  to be dynamic, just like irq number descriptors. The
  platform-wide definition of number of pins goes away - this is
  now just the sum total of the pins registered to the subsystem.
- Make sure mappings with only a function name and no device
  works properly.

ChangeLog v3->v4:

- Define a number space per controller instead of globally,
  Stephen and Grant requested the same thing so now maps need to
  define target controller, and the radix tree of pin descriptors
  is a property on each pin controller device.
- Add a compulsory pinctrl device entry to the pinctrl mapping
  table. This must match the pinctrl device, like "pinctrl.0"
- Split the file core.c in two: core.c and pinmux.c where the
  latter carry all pinmux stuff, the core is for generic pin
  control, and use local headers to access functionality between
  files. It is now possible to implement a "blank" pin controller
  without pinmux capabilities. This split will make new additions
  like pindrive.c, pinbias.c etc possible for combined drivers
  and chunks of functionality which is a GoodThing(TM).
- Rewrite the interaction with the GPIO subsystem - the pin
  controller descriptor now handles this by defining an offset
  into the GPIO numberspace for its handled pin range. This is
  used to look up the apropriate pin controller for a GPIO pin.
  Then that specific GPIO range is matched 1-1 for the target
  controller instance.
- Fixed a number of review comments from Joe Perches.
- Broke out a header file pinctrl.h for the core pin handling
  stuff that will be reused by other stuff than pinmux.
- Fixed some erroneous EXPORT() stuff.
- Remove mispatched U300 Kconfig and Makefile entries
- Fixed a number of review comments from Stephen Warren, not all
  of them - still WIP. But I think the new mapping that will
  specify which function goes to which pin mux controller address
  50% of your concerns (else beat me up).

ChangeLog v4->v5:

- Defined a "position" for each function, so the pin controller now
  tracks a function in a certain position, and the pinmux maps define
  what position you want the function in. (Feedback from Stephen
  Warren and Sascha Hauer).
- Since we now need to request a combined function+position from
  the machine mapping table that connect mux settings to drivers,
  it was extended with a position field and a name field. The
  name field is now used if you e.g. need to switch between two
  mux map settings at runtime.
- Switched from a class device to using struct bus_type for this
  subsystem. Verified sysfs functionality: seems to work fine.
  (Feedback from Arnd Bergmann and Greg Kroah-Hartman)
- Define a per pincontroller list of GPIO ranges from the GPIO
  pin space that can be handled by the pin controller. These can
  be added one by one at runtime. (Feedback from Barry Song)
- Expanded documentation of regulator_[get|enable|disable|put]
  semantics.
- Fixed a number of review comments from Barry Song. (Thanks!)

ChangeLog v5->v6:

- Create an abstract pin group concept that can sort pins into
  named and enumerated groups no matter what the use of these
  groups may be, one possible usecase is a group of pins being
  muxed in or so. The intention is however to also use these
  groups for other pin control activities.
- Make it compulsory for pinmux functions to associate with
  at least one group, so the abstract pin group concept is used
  to define the groups of pins affected by a pinmux function.
  The pinmux driver interface has been altered so as to enforce
  a function to list applicable groups per function.
- Provide an optional .group entry in the pinmux machine map
  so the map can select beteween different available groups
  to be used with a certain function.
- Consequent changes all over the place so that e.g. debugfs
  present reasonable information about the world.
- Drop the per-pin mux (*config) function in the pinmux_ops
  struct - I was afraid that this would start to be used for
  things totally unrelated to muxing, we can introduce that to
  the generic struct pinctrl_ops if needed. I want to keep
  muxing orthogonal to other pin control subjects and not mix
  these things up.

ChangeLog v6->v7:

- Make it possible to have several map entries matching the
  same device, pin controller and function, but using
  a different group, and alter the semantics so that
  pinmux_get() will pick all matching map entries, and
  store the associated groups in a list. The list will
  then be iterated over at pinmux_enable()/pinmux_disable()
  and corresponding driver functions called for each
  defined group. Notice that you're only allowed to map
  multiple *groups* to the same
  { device, pin controller, function } triplet, attempts
  to map the same device to multiple pin controllers will
  for example fail. This is hopefully the crucial feature
  requested by Stephen Warren.
- Add a pinmux hogging field to the pinmux mapping entries,
  and enable the pinmux core to hog pinmux map entries.
  This currently only works for pinmuxes without assigned
  devices as it looks now, but with device trees we can
  look up the corresponding struct device * entries when
  we register the pinmux driver, and have it hog each
  pinmux map in turn, for a simple approach to
  non-dynamic pin muxing. This addresses an issue from
  Grant Likely that the machine should take care of as
  much of the pinmux setup as possible, not the devices.
  By supplying a list of hogs, it can now instruct the
  core to take care of any static mappings.
- Switch pinmux group retrieveal function to grab an
  array of strings representing the groups rather than an
  array of unsigned and rewrite accordingly.
- Alter debugfs to show the grouplist handled by each
  pinmux. Also add a list of hogs.
- Dynamically allocate a struct pinmux at pinmux_get() and
  free it at pinmux_put(), then add these to the global
  list of pinmuxes active as we go along.
- Go over the list of pinmux maps at pinmux_get() time
  and repeatedly apply matches.
- Retrieve applicable groups per function from the driver
  as a string array rather than a unsigned array, then
  lookup the enumerators.
- Make the device to pinmux map a singleton - only allow the
  mapping table to be registered once and even tag the
  registration function with __init so it surely won't be
  abused.
- Create a separate debugfs file to view the pinmux map at
  runtime.
- Introduce a spin lock to the pin descriptor struct, lock it
  when modifying pin status entries. Reported by Stijn Devriendt.
- Fix up the documentation after review from Stephen Warren.
- Let the GPIO ranges give names as const char * instead of some
  fixed-length string.
- add a function to unregister GPIO ranges to mirror the
  registration function.
- Privatized the struct pinctrl_device and removed it from the
  <linux/pinctrl/pinctrl.h> API, the drivers do not need to know
  the members of this struct. It is now in the local header
  "core.h".
- Rename the concept of "anonymous" mux maps to "system" muxes
  and add convenience macros and documentation.

ChangeLog v7->v8:

- Delete the leftover pinmux_config() function from the
 <linux/pinctrl/pinmux.h> header.
- Fix a race condition found by Stijn Devriendt in pin_request()

ChangeLog v8->v9:

- Drop the bus_type and the sysfs attributes and all, we're not on
  the clear about how this should be used for e.g. userspace
  interfaces so let us save this for the future.
- Use the right name in MAINTAINERS, PIN CONTROL rather than
  PINMUX
- Don't kfree() the device state holder, let the .remove() callback
  handle this.
- Fix up numerous kerneldoc headers to have one line for the function
  description and more verbose documentation below the parameters

ChangeLog v9->v10:
- pinctrl: EXPORT_SYMBOL needs export.h, folded in a patch
  from Steven Rothwell
- fix pinctrl_register error handling, folded in a patch from
  Axel Lin
- Various fixes to documentation text so that it's consistent.
- Removed pointless comment from drivers/Kconfig
- Removed dependency on SYSFS since we removed the bus in
  v9.
- Renamed hopelessly abbreviated pctldev_* functions to the
  more verbose pinctrl_dev_*
- Drop mutex properly when looking up GPIO ranges
- Return NULL instead of ERR_PTR() errors on registration of
  pin controllers, using cast pointers is fragile. We can
  live without the detailed error codes for sure.

Cc: Stijn Devriendt <highguy@gmail.com>
Cc: Joe Perches <joe@perches.com>
Cc: Russell King <linux@arm.linux.org.uk>
Acked-by: NGrant Likely <grant.likely@secretlab.ca>
Acked-by: NStephen Warren <swarren@nvidia.com>
Tested-by: NBarry Song <21cnbao@gmail.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>