Re: [PATCH 14/14] pwm: meson: add documentation to the driver
From: Neil Armstrong
Date: Mon May 27 2019 - 08:37:14 EST
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-KÃnig <u.kleine-koenig@xxxxxxxxxxxxxx>
> Co-authored-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx>
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@xxxxxxxxxxxxxx>
> 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 <narmstrong@xxxxxxxxxxxx>
> * Copyright (C) 2014 Amlogic, Inc.
Reviewed-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx>