Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757821Ab1CaNze (ORCPT ); Thu, 31 Mar 2011 09:55:34 -0400 Received: from smtp.nokia.com ([147.243.1.47]:64090 "EHLO mgw-sa01.nokia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757729Ab1CaNzd (ORCPT ); Thu, 31 Mar 2011 09:55:33 -0400 From: Ameya Palande To: linux-kernel@vger.kernel.org Cc: linux-doc@vger.kernel.org, samu.p.onkalo@nokia.com, rdunlap@xenotime.net Subject: [PATCH] Documentation: Gather led information in one place Date: Thu, 31 Mar 2011 16:55:24 +0300 Message-Id: <1301579724-29893-1-git-send-email-ameya.palande@nokia.com> X-Mailer: git-send-email 1.7.1 X-Nokia-AV: Clean Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 13260 Lines: 340 Signed-off-by: Ameya Palande --- Documentation/leds-class.txt | 98 ------------------------------------ Documentation/leds-lp3944.txt | 50 ------------------ Documentation/leds/leds-class.txt | 98 ++++++++++++++++++++++++++++++++++++ Documentation/leds/leds-lp3944.txt | 50 ++++++++++++++++++ 4 files changed, 148 insertions(+), 148 deletions(-) delete mode 100644 Documentation/leds-class.txt delete mode 100644 Documentation/leds-lp3944.txt create mode 100644 Documentation/leds/leds-class.txt create mode 100644 Documentation/leds/leds-lp3944.txt diff --git a/Documentation/leds-class.txt b/Documentation/leds-class.txt deleted file mode 100644 index 58b266b..0000000 --- a/Documentation/leds-class.txt +++ /dev/null @@ -1,98 +0,0 @@ - -LED handling under Linux -======================== - -If you're reading this and thinking about keyboard leds, these are -handled by the input subsystem and the led class is *not* needed. - -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 ide-disk, -nand-disk and sharpsl-charge triggers. With led triggers disabled, the code -optimises away. - -Complex triggers whilst 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//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//trigger). Trigger specific -parameters can appear in /sys/class/leds/ 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. - - -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 ). To set an LED to blinking, -however, it is better to use use the API function led_blink_set(), -as it will check and implement software fallback if necessary. - -To turn off blinking again, use the API function led_brightness_set() -as that will not just set the LED brightness but also 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. - diff --git a/Documentation/leds-lp3944.txt b/Documentation/leds-lp3944.txt deleted file mode 100644 index c6eda18..0000000 --- a/Documentation/leds-lp3944.txt +++ /dev/null @@ -1,50 +0,0 @@ -Kernel driver lp3944 -==================== - - * National Semiconductor LP3944 Fun-light Chip - Prefix: 'lp3944' - Addresses scanned: None (see the Notes section below) - Datasheet: Publicly available at the National Semiconductor website - http://www.national.com/pf/LP/LP3944.html - -Authors: - Antonio Ospite - - -Description ------------ -The LP3944 is a helper chip that can drive up to 8 leds, with two programmable -DIM modes; it could even be used as a gpio expander but this driver assumes it -is used as a led controller. - -The DIM modes are used to set _blink_ patterns for leds, the pattern is -specified supplying two parameters: - - period: from 0s to 1.6s - - duty cycle: percentage of the period the led is on, from 0 to 100 - -Setting a led in DIM0 or DIM1 mode makes it blink according to the pattern. -See the datasheet for details. - -LP3944 can be found on Motorola A910 smartphone, where it drives the rgb -leds, the camera flash light and the lcds power. - - -Notes ------ -The chip is used mainly in embedded contexts, so this driver expects it is -registered using the i2c_board_info mechanism. - -To register the chip at address 0x60 on adapter 0, set the platform data -according to include/linux/leds-lp3944.h, set the i2c board info: - - static struct i2c_board_info __initdata a910_i2c_board_info[] = { - { - I2C_BOARD_INFO("lp3944", 0x60), - .platform_data = &a910_lp3944_leds, - }, - }; - -and register it in the platform init function - - i2c_register_board_info(0, a910_i2c_board_info, - ARRAY_SIZE(a910_i2c_board_info)); diff --git a/Documentation/leds/leds-class.txt b/Documentation/leds/leds-class.txt new file mode 100644 index 0000000..58b266b --- /dev/null +++ b/Documentation/leds/leds-class.txt @@ -0,0 +1,98 @@ + +LED handling under Linux +======================== + +If you're reading this and thinking about keyboard leds, these are +handled by the input subsystem and the led class is *not* needed. + +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 ide-disk, +nand-disk and sharpsl-charge triggers. With led triggers disabled, the code +optimises away. + +Complex triggers whilst 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//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//trigger). Trigger specific +parameters can appear in /sys/class/leds/ 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. + + +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 ). To set an LED to blinking, +however, it is better to use use the API function led_blink_set(), +as it will check and implement software fallback if necessary. + +To turn off blinking again, use the API function led_brightness_set() +as that will not just set the LED brightness but also 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. + diff --git a/Documentation/leds/leds-lp3944.txt b/Documentation/leds/leds-lp3944.txt new file mode 100644 index 0000000..c6eda18 --- /dev/null +++ b/Documentation/leds/leds-lp3944.txt @@ -0,0 +1,50 @@ +Kernel driver lp3944 +==================== + + * National Semiconductor LP3944 Fun-light Chip + Prefix: 'lp3944' + Addresses scanned: None (see the Notes section below) + Datasheet: Publicly available at the National Semiconductor website + http://www.national.com/pf/LP/LP3944.html + +Authors: + Antonio Ospite + + +Description +----------- +The LP3944 is a helper chip that can drive up to 8 leds, with two programmable +DIM modes; it could even be used as a gpio expander but this driver assumes it +is used as a led controller. + +The DIM modes are used to set _blink_ patterns for leds, the pattern is +specified supplying two parameters: + - period: from 0s to 1.6s + - duty cycle: percentage of the period the led is on, from 0 to 100 + +Setting a led in DIM0 or DIM1 mode makes it blink according to the pattern. +See the datasheet for details. + +LP3944 can be found on Motorola A910 smartphone, where it drives the rgb +leds, the camera flash light and the lcds power. + + +Notes +----- +The chip is used mainly in embedded contexts, so this driver expects it is +registered using the i2c_board_info mechanism. + +To register the chip at address 0x60 on adapter 0, set the platform data +according to include/linux/leds-lp3944.h, set the i2c board info: + + static struct i2c_board_info __initdata a910_i2c_board_info[] = { + { + I2C_BOARD_INFO("lp3944", 0x60), + .platform_data = &a910_lp3944_leds, + }, + }; + +and register it in the platform init function + + i2c_register_board_info(0, a910_i2c_board_info, + ARRAY_SIZE(a910_i2c_board_info)); -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/