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Commit 4ae42ce7 authored by Martin Blumenstingl's avatar Martin Blumenstingl Committed by Thierry Reding
Browse files

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: default avatarUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Co-authored-by: default avatarNeil Armstrong <narmstrong@baylibre.com>
Reviewed-by: default avatarNeil Armstrong <narmstrong@baylibre.com>
Signed-off-by: default avatarMartin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: default avatarThierry Reding <thierry.reding@gmail.com>
parent 7341c785

drivers/pwm/pwm-meson.c

+22 −0
Original line number Diff line number Diff line 
// 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.