Merge tag 'leds-for-5.3-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/j.anaszewski/linux-leds

Pull LED updates from Jacek Anaszewski:

 - Add a new LED common module for ti-lmu driver family

 - Modify MFD ti-lmu bindings
        - add ti,brightness-resolution
        - add the ramp up/down property

 - Add regulator support for LM36274 driver to lm363x-regulator.c

 - New LED class drivers with DT bindings:
        - leds-spi-byte
        - leds-lm36274
        - leds-lm3697 (move the support from MFD to LED subsystem)

 - Simplify getting the I2C adapter of a client:
        - leds-tca6507
        - leds-pca955x

 - Convert LED documentation to ReST

* tag 'leds-for-5.3-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/j.anaszewski/linux-leds:
  dt: leds-lm36274.txt: fix a broken reference to ti-lmu.txt
  docs: leds: convert to ReST
  leds: leds-tca6507: simplify getting the adapter of a client
  leds: leds-pca955x: simplify getting the adapter of a client
  leds: lm36274: Introduce the TI LM36274 LED driver
  dt-bindings: leds: Add LED bindings for the LM36274
  regulator: lm363x: Add support for LM36274
  mfd: ti-lmu: Add LM36274 support to the ti-lmu
  dt-bindings: mfd: Add lm36274 bindings to ti-lmu
  leds: max77650: Remove set but not used variable 'parent'
  leds: avoid flush_work in atomic context
  leds: lm3697: Introduce the lm3697 driver
  mfd: ti-lmu: Remove support for LM3697
  dt-bindings: ti-lmu: Modify dt bindings for the LM3697
  leds: TI LMU: Add common code for TI LMU devices
  leds: spi-byte: add single byte SPI LED driver
  dt-bindings: leds: Add binding for spi-byte LED.
  dt-bindings: mfd: LMU: Add ti,brightness-resolution
  dt-bindings: mfd: LMU: Add the ramp up/down property

1 files changed, 125 insertions, 0 deletions

diff --git a/Documentation/leds/leds-class.rst b/Documentation/leds/leds-class.rst
new file mode 100644
index 000000000000..df0120a1ee3c
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+++ b/Documentation/leds/leds-class.rst
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+========================
+LED handling under Linux
+========================
+
+In its simplest form, the LED class just allows control of LEDs from
+userspace. LEDs appear in /sys/class/leds/. The maximum brightness of the
+LED is defined in max_brightness file. The brightness file will set the brightness
+of the LED (taking a value 0-max_brightness). Most LEDs don't have hardware
+brightness support so will just be turned on for non-zero brightness settings.
+
+The class also introduces the optional concept of an LED trigger. A trigger
+is a kernel based source of led events. Triggers can either be simple or
+complex. A simple trigger isn't configurable and is designed to slot into
+existing subsystems with minimal additional code. Examples are the disk-activity,
+nand-disk and sharpsl-charge triggers. With led triggers disabled, the code
+optimises away.
+
+Complex triggers while available to all LEDs have LED specific
+parameters and work on a per LED basis. The timer trigger is an example.
+The timer trigger will periodically change the LED brightness between
+LED_OFF and the current brightness setting. The "on" and "off" time can
+be specified via /sys/class/leds/<device>/delay_{on,off} in milliseconds.
+You can change the brightness value of a LED independently of the timer
+trigger. However, if you set the brightness value to LED_OFF it will
+also disable the timer trigger.
+
+You can change triggers in a similar manner to the way an IO scheduler
+is chosen (via /sys/class/leds/<device>/trigger). Trigger specific
+parameters can appear in /sys/class/leds/<device> once a given trigger is
+selected.
+
+
+Design Philosophy
+=================
+
+The underlying design philosophy is simplicity. LEDs are simple devices
+and the aim is to keep a small amount of code giving as much functionality
+as possible.  Please keep this in mind when suggesting enhancements.
+
+
+LED Device Naming
+=================
+
+Is currently of the form:
+
+	"devicename:colour:function"
+
+There have been calls for LED properties such as colour to be exported as
+individual led class attributes. As a solution which doesn't incur as much
+overhead, I suggest these become part of the device name. The naming scheme
+above leaves scope for further attributes should they be needed. If sections
+of the name don't apply, just leave that section blank.
+
+
+Brightness setting API
+======================
+
+LED subsystem core exposes following API for setting brightness:
+
+    - led_set_brightness:
+		it is guaranteed not to sleep, passing LED_OFF stops
+		blinking,
+
+    - led_set_brightness_sync:
+		for use cases when immediate effect is desired -
+		it can block the caller for the time required for accessing
+		device registers and can sleep, passing LED_OFF stops hardware
+		blinking, returns -EBUSY if software blink fallback is enabled.
+
+
+LED registration API
+====================
+
+A driver wanting to register a LED classdev for use by other drivers /
+userspace needs to allocate and fill a led_classdev struct and then call
+`[devm_]led_classdev_register`. If the non devm version is used the driver
+must call led_classdev_unregister from its remove function before
+free-ing the led_classdev struct.
+
+If the driver can detect hardware initiated brightness changes and thus
+wants to have a brightness_hw_changed attribute then the LED_BRIGHT_HW_CHANGED
+flag must be set in flags before registering. Calling
+led_classdev_notify_brightness_hw_changed on a classdev not registered with
+the LED_BRIGHT_HW_CHANGED flag is a bug and will trigger a WARN_ON.
+
+Hardware accelerated blink of LEDs
+==================================
+
+Some LEDs can be programmed to blink without any CPU interaction. To
+support this feature, a LED driver can optionally implement the
+blink_set() function (see <linux/leds.h>). To set an LED to blinking,
+however, it is better to use the API function led_blink_set(), as it
+will check and implement software fallback if necessary.
+
+To turn off blinking, use the API function led_brightness_set()
+with brightness value LED_OFF, which should stop any software
+timers that may have been required for blinking.
+
+The blink_set() function should choose a user friendly blinking value
+if it is called with `*delay_on==0` && `*delay_off==0` parameters. In this
+case the driver should give back the chosen value through delay_on and
+delay_off parameters to the leds subsystem.
+
+Setting the brightness to zero with brightness_set() callback function
+should completely turn off the LED and cancel the previously programmed
+hardware blinking function, if any.
+
+
+Known Issues
+============
+
+The LED Trigger core cannot be a module as the simple trigger functions
+would cause nightmare dependency issues. I see this as a minor issue
+compared to the benefits the simple trigger functionality brings. The
+rest of the LED subsystem can be modular.
+
+
+Future Development
+==================
+
+At the moment, a trigger can't be created specifically for a single LED.
+There are a number of cases where a trigger might only be mappable to a
+particular LED (ACPI?). The addition of triggers provided by the LED driver
+should cover this option and be possible to add without breaking the
+current interface.