diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/devicetree/bindings/pwm/lpc32xx-pwm.txt | 12 | ||||
| -rw-r--r-- | Documentation/devicetree/bindings/pwm/mxs-pwm.txt | 17 | ||||
| -rw-r--r-- | Documentation/devicetree/bindings/pwm/nvidia,tegra20-pwm.txt | 18 | ||||
| -rw-r--r-- | Documentation/devicetree/bindings/pwm/pwm.txt | 57 | ||||
| -rw-r--r-- | Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt | 28 | ||||
| -rw-r--r-- | Documentation/pwm.txt | 76 |
6 files changed, 208 insertions, 0 deletions
diff --git a/Documentation/devicetree/bindings/pwm/lpc32xx-pwm.txt b/Documentation/devicetree/bindings/pwm/lpc32xx-pwm.txt new file mode 100644 index 000000000000..cfe1db3bb6e9 --- /dev/null +++ b/Documentation/devicetree/bindings/pwm/lpc32xx-pwm.txt @@ -0,0 +1,12 @@ +LPC32XX PWM controller + +Required properties: +- compatible: should be "nxp,lpc3220-pwm" +- reg: physical base address and length of the controller's registers + +Examples: + +pwm@0x4005C000 { + compatible = "nxp,lpc3220-pwm"; + reg = <0x4005C000 0x8>; +}; diff --git a/Documentation/devicetree/bindings/pwm/mxs-pwm.txt b/Documentation/devicetree/bindings/pwm/mxs-pwm.txt new file mode 100644 index 000000000000..b16f4a57d111 --- /dev/null +++ b/Documentation/devicetree/bindings/pwm/mxs-pwm.txt @@ -0,0 +1,17 @@ +Freescale MXS PWM controller + +Required properties: +- compatible: should be "fsl,imx23-pwm" +- reg: physical base address and length of the controller's registers +- #pwm-cells: should be 2. The first cell specifies the per-chip index + of the PWM to use and the second cell is the duty cycle in nanoseconds. +- fsl,pwm-number: the number of PWM devices + +Example: + +pwm: pwm@80064000 { + compatible = "fsl,imx28-pwm", "fsl,imx23-pwm"; + reg = <0x80064000 2000>; + #pwm-cells = <2>; + fsl,pwm-number = <8>; +}; diff --git a/Documentation/devicetree/bindings/pwm/nvidia,tegra20-pwm.txt b/Documentation/devicetree/bindings/pwm/nvidia,tegra20-pwm.txt new file mode 100644 index 000000000000..bbbeedb4ec05 --- /dev/null +++ b/Documentation/devicetree/bindings/pwm/nvidia,tegra20-pwm.txt @@ -0,0 +1,18 @@ +Tegra SoC PWFM controller + +Required properties: +- compatible: should be one of: + - "nvidia,tegra20-pwm" + - "nvidia,tegra30-pwm" +- reg: physical base address and length of the controller's registers +- #pwm-cells: On Tegra the number of cells used to specify a PWM is 2. The + first cell specifies the per-chip index of the PWM to use and the second + cell is the duty cycle in nanoseconds. + +Example: + + pwm: pwm@7000a000 { + compatible = "nvidia,tegra20-pwm"; + reg = <0x7000a000 0x100>; + #pwm-cells = <2>; + }; diff --git a/Documentation/devicetree/bindings/pwm/pwm.txt b/Documentation/devicetree/bindings/pwm/pwm.txt new file mode 100644 index 000000000000..73ec962bfe8c --- /dev/null +++ b/Documentation/devicetree/bindings/pwm/pwm.txt @@ -0,0 +1,57 @@ +Specifying PWM information for devices +====================================== + +1) PWM user nodes +----------------- + +PWM users should specify a list of PWM devices that they want to use +with a property containing a 'pwm-list': + + pwm-list ::= <single-pwm> [pwm-list] + single-pwm ::= <pwm-phandle> <pwm-specifier> + pwm-phandle : phandle to PWM controller node + pwm-specifier : array of #pwm-cells specifying the given PWM + (controller specific) + +PWM properties should be named "pwms". The exact meaning of each pwms +property must be documented in the device tree binding for each device. +An optional property "pwm-names" may contain a list of strings to label +each of the PWM devices listed in the "pwms" property. If no "pwm-names" +property is given, the name of the user node will be used as fallback. + +Drivers for devices that use more than a single PWM device can use the +"pwm-names" property to map the name of the PWM device requested by the +pwm_get() call to an index into the list given by the "pwms" property. + +The following example could be used to describe a PWM-based backlight +device: + + pwm: pwm { + #pwm-cells = <2>; + }; + + [...] + + bl: backlight { + pwms = <&pwm 0 5000000>; + pwm-names = "backlight"; + }; + +pwm-specifier typically encodes the chip-relative PWM number and the PWM +period in nanoseconds. Note that in the example above, specifying the +"pwm-names" is redundant because the name "backlight" would be used as +fallback anyway. + +2) PWM controller nodes +----------------------- + +PWM controller nodes must specify the number of cells used for the +specifier using the '#pwm-cells' property. + +An example PWM controller might look like this: + + pwm: pwm@7000a000 { + compatible = "nvidia,tegra20-pwm"; + reg = <0x7000a000 0x100>; + #pwm-cells = <2>; + }; diff --git a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt new file mode 100644 index 000000000000..1e4fc727f3b1 --- /dev/null +++ b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt @@ -0,0 +1,28 @@ +pwm-backlight bindings + +Required properties: + - compatible: "pwm-backlight" + - pwms: OF device-tree PWM specification (see PWM binding[0]) + - brightness-levels: Array of distinct brightness levels. Typically these + are in the range from 0 to 255, but any range starting at 0 will do. + The actual brightness level (PWM duty cycle) will be interpolated + from these values. 0 means a 0% duty cycle (darkest/off), while the + last value in the array represents a 100% duty cycle (brightest). + - default-brightness-level: the default brightness level (index into the + array defined by the "brightness-levels" property) + +Optional properties: + - pwm-names: a list of names for the PWM devices specified in the + "pwms" property (see PWM binding[0]) + +[0]: Documentation/devicetree/bindings/pwm/pwm.txt + +Example: + + backlight { + compatible = "pwm-backlight"; + pwms = <&pwm 0 5000000>; + + brightness-levels = <0 4 8 16 32 64 128 255>; + default-brightness-level = <6>; + }; diff --git a/Documentation/pwm.txt b/Documentation/pwm.txt new file mode 100644 index 000000000000..554290ebab94 --- /dev/null +++ b/Documentation/pwm.txt @@ -0,0 +1,76 @@ +Pulse Width Modulation (PWM) interface + +This provides an overview about the Linux PWM interface + +PWMs are commonly used for controlling LEDs, fans or vibrators in +cell phones. PWMs with a fixed purpose have no need implementing +the Linux PWM API (although they could). However, PWMs are often +found as discrete devices on SoCs which have no fixed purpose. It's +up to the board designer to connect them to LEDs or fans. To provide +this kind of flexibility the generic PWM API exists. + +Identifying PWMs +---------------- + +Users of the legacy PWM API use unique IDs to refer to PWM devices. + +Instead of referring to a PWM device via its unique ID, board setup code +should instead register a static mapping that can be used to match PWM +consumers to providers, as given in the following example: + + static struct pwm_lookup board_pwm_lookup[] = { + PWM_LOOKUP("tegra-pwm", 0, "pwm-backlight", NULL), + }; + + static void __init board_init(void) + { + ... + pwm_add_table(board_pwm_lookup, ARRAY_SIZE(board_pwm_lookup)); + ... + } + +Using PWMs +---------- + +Legacy users can request a PWM device using pwm_request() and free it +after usage with pwm_free(). + +New users should use the pwm_get() function and pass to it the consumer +device or a consumer name. pwm_put() is used to free the PWM device. + +After being requested a PWM has to be configured using: + +int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns); + +To start/stop toggling the PWM output use pwm_enable()/pwm_disable(). + +Implementing a PWM driver +------------------------- + +Currently there are two ways to implement pwm drivers. Traditionally +there only has been the barebone API meaning that each driver has +to implement the pwm_*() functions itself. This means that it's impossible +to have multiple PWM drivers in the system. For this reason it's mandatory +for new drivers to use the generic PWM framework. + +A new PWM controller/chip can be added using pwmchip_add() and removed +again with pwmchip_remove(). pwmchip_add() takes a filled in struct +pwm_chip as argument which provides a description of the PWM chip, the +number of PWM devices provider by the chip and the chip-specific +implementation of the supported PWM operations to the framework. + +Locking +------- + +The PWM core list manipulations are protected by a mutex, so pwm_request() +and pwm_free() may not be called from an atomic context. Currently the +PWM core does not enforce any locking to pwm_enable(), pwm_disable() and +pwm_config(), so the calling context is currently driver specific. This +is an issue derived from the former barebone API and should be fixed soon. + +Helpers +------- + +Currently a PWM can only be configured with period_ns and duty_ns. For several +use cases freq_hz and duty_percent might be better. Instead of calculating +this in your driver please consider adding appropriate helpers to the framework. |