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-koe...@pengutronix.de> Co-authored-by: Neil Armstrong <narmstr...@baylibre.com> Reviewed-by: Neil Armstrong <narmstr...@baylibre.com> Signed-off-by: Martin Blumenstingl <martin.blumensti...@googlemail.com> --- drivers/pwm/pwm-meson.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c index bb48ba85f756..31259026484c 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 <narmstr...@baylibre.com> * Copyright (C) 2014 Amlogic, Inc. -- 2.22.0
