Add documentation for PWM normal and complementary modes.
Signed-off-by: Claudiu Beznea <claudiu.beznea@xxxxxxxxxxxxx>
---
Documentation/devicetree/bindings/pwm/pwm.txt | 17 ++++++++++++++--
Documentation/pwm.txt | 29 +++++++++++++++++++++++++--
2 files changed, 42 insertions(+), 4 deletions(-)
diff --git a/Documentation/devicetree/bindings/pwm/pwm.txt b/Documentation/devicetree/bindings/pwm/pwm.txt
index 8556263b8502..fdff25bad1db 100644
--- a/Documentation/devicetree/bindings/pwm/pwm.txt
+++ b/Documentation/devicetree/bindings/pwm/pwm.txt
@@ -43,8 +43,8 @@ because the name "backlight" would be used as fallback anyway.
pwm-specifier typically encodes the chip-relative PWM number and the PWM
period in nanoseconds.
-Optionally, the pwm-specifier can encode a number of flags (defined in
-<dt-bindings/pwm/pwm.h>) in a third cell:
+Optionally, the pwm-specifier can encode:
+1. a number of flags (defined in <dt-bindings/pwm/pwm.h>) in a third cell:
- PWM_POLARITY_INVERTED: invert the PWM signal polarity
Example with optional PWM specifier for inverse polarity
@@ -54,6 +54,19 @@ Example with optional PWM specifier for inverse polarity
pwm-names = "backlight";
};
+2. PWM working modes (defined in <dt-bindings/pwm/pwm.h>) in the 4th cell:
+- PWM_MODE_NORMAL: for all PWM controllers
+- PWM_MODE_COMPLEMENTARY: for PWM controllers with more than one output per
+PWM channel
+
+Example with PWM modes:
+
+ bl: blacklight {
+ pwms = <&pwm 0 5000000 PWM_POLARITY_INVERTED
+ PWM_DTMODE_NORMAL | PWM_DTMODE_COMPLEMENTARY>;
+ pwm-names = "backlight";
+ };
+
2) PWM controller nodes
-----------------------
diff --git a/Documentation/pwm.txt b/Documentation/pwm.txt
index 8fbf0aa3ba2d..58c9bd55f021 100644
--- a/Documentation/pwm.txt
+++ b/Documentation/pwm.txt
@@ -61,8 +61,8 @@ In addition to the PWM state, the PWM API also exposes PWM arguments, which
are the reference PWM config one should use on this PWM.
PWM arguments are usually platform-specific and allows the PWM user to only
care about dutycycle relatively to the full period (like, duty = 50% of the
-period). struct pwm_args contains 2 fields (period and polarity) and should
-be used to set the initial PWM config (usually done in the probe function
+period). struct pwm_args contains 3 fields (period, polarity and mode) and
+should be used to set the initial PWM config (usually done in the probe function
of the PWM user). PWM arguments are retrieved with pwm_get_args().
Using PWMs with the sysfs interface
@@ -83,6 +83,9 @@ will find:
unexport
Unexports a PWM channel from sysfs (write-only).
+ mode
+ PWM chip supported modes.
+
The PWM channels are numbered using a per-chip index from 0 to npwm-1.
When a PWM channel is exported a pwmX directory will be created in the
@@ -110,6 +113,28 @@ channel that was exported. The following properties will then be available:
- 0 - disabled
- 1 - enabled
+ mode
+ Set PWM channel working mode (normal and complementary). PWM chip with
+ complementary mode could also work in normal mode by using only one physical
+ output.
+
+ Normal mode - for PWM chips with one output per PWM channel; output
+ waveforms looks like this:
+ __ __ __ __
+ PWM __| |__| |__| |__| |__
+ <--T-->
+
+ Complementary mode - for PWM chips with more than one output per PWM
+ channel; output waveforms for a PWM controller with 2 outputs per PWM
+ channel looks line this:
+ __ __ __ __
+ PWMH1 __| |__| |__| |__| |__
+ __ __ __ __ __
+ PWML1 |__| |__| |__| |__|
+ <--T-->
+
+ Where T is the signal period.
+
Implementing a PWM driver
-------------------------
--
2.7.4
--
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