diff options
| author |   Martin Blumenstingl <martin.blumenstingl@googlemail.com> | 2019-06-12 21:59:11 +0200 |
|---|---|---|
| committer |   Thierry Reding <thierry.reding@gmail.com> | 2019-06-26 11:39:10 +0200 |
| commit | 4ae42ce793a755decb2c5978623e56edfdf3ab39 (patch) | |
| tree | 1ae13ccea70ffa4812a9b003d1bbdf7b3cf3f56b /drivers/pwm | |
| parent | pwm: meson: Add support PWM_POLARITY_INVERSED when disabling (diff) | |
| download | linux-dev-4ae42ce793a755decb2c5978623e56edfdf3ab39.tar.xz linux-dev-4ae42ce793a755decb2c5978623e56edfdf3ab39.zip | |
pwm: meson: Add documentation to the driver
Add links to the datasheet and a short summary how the hardware works.
The goal is to make it easier for other developers to understand why the
pwm-meson driver is implemented the way it is.
Suggested-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Co-authored-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Diffstat (limited to 'drivers/pwm')
| -rw-r--r-- | drivers/pwm/pwm-meson.c | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c index f934828aaff9..3cbff5cbb789 100644 --- a/drivers/pwm/pwm-meson.c +++ b/drivers/pwm/pwm-meson.c @@ -1,5 +1,27 @@ // SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause /* + * PWM controller driver for Amlogic Meson SoCs. + * + * This PWM is only a set of Gates, Dividers and Counters: + * PWM output is achieved by calculating a clock that permits calculating + * two periods (low and high). The counter then has to be set to switch after + * N cycles for the first half period. + * The hardware has no "polarity" setting. This driver reverses the period + * cycles (the low length is inverted with the high length) for + * PWM_POLARITY_INVERSED. This means that .get_state cannot read the polarity + * from the hardware. + * Setting the duty cycle will disable and re-enable the PWM output. + * Disabling the PWM stops the output immediately (without waiting for the + * current period to complete first). + * + * The public S912 (GXM) datasheet contains some documentation for this PWM + * controller starting on page 543: + * https://dl.khadas.com/Hardware/VIM2/Datasheet/S912_Datasheet_V0.220170314publicversion-Wesion.pdf + * An updated version of this IP block is found in S922X (G12B) SoCs. The + * datasheet contains the description for this IP block revision starting at + * page 1084: + * https://dn.odroid.com/S922X/ODROID-N2/Datasheet/S922X_Public_Datasheet_V0.2.pdf + * * Copyright (c) 2016 BayLibre, SAS. * Author: Neil Armstrong <narmstrong@baylibre.com> * Copyright (C) 2014 Amlogic, Inc. |