On 25/05/2019 20:11, Martin Blumenstingl wrote: > Add a link 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> > Signed-off-by: Martin Blumenstingl <martin.blumensti...@googlemail.com> > --- > drivers/pwm/pwm-meson.c | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c > index bb48ba85f756..6a978caba483 100644 > --- a/drivers/pwm/pwm-meson.c > +++ b/drivers/pwm/pwm-meson.c > @@ -1,5 +1,23 @@ > // 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 S922X datasheet contains some documentation for this PWM > + * controller starting on page 1084: > + * > https://dl.khadas.com/Hardware/VIM2/Datasheet/S912_Datasheet_V0.220170314publicversion-Wesion.pdf > + * > * Copyright (c) 2016 BayLibre, SAS. > * Author: Neil Armstrong <narmstr...@baylibre.com> > * Copyright (C) 2014 Amlogic, Inc. >
Reviewed-by: Neil Armstrong <narmstr...@baylibre.com>
