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From: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
To: linux-amlogic@lists.infradead.org, linux-pwm@vger.kernel.org,
	thierry.reding@gmail.com
Cc: linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	u.kleine-koenig@pengutronix.de, narmstrong@baylibre.com,
	Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Subject: [PATCH v3 14/14] pwm: meson: add documentation to the driver
Date: Wed, 12 Jun 2019 21:59:11 +0200	[thread overview]
Message-ID: <20190612195911.4442-15-martin.blumenstingl@googlemail.com> (raw)
In-Reply-To: <20190612195911.4442-1-martin.blumenstingl@googlemail.com>

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>
---
 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 <narmstrong@baylibre.com>
  * Copyright (C) 2014 Amlogic, Inc.
-- 
2.22.0


      parent reply	other threads:[~2019-06-12 19:59 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-12 19:58 [PATCH v3 00/14] pwm-meson: cleanups and improvements Martin Blumenstingl
2019-06-12 19:58 ` [PATCH v3 01/14] pwm: meson: unify the parameter list of meson_pwm_{enable,disable} Martin Blumenstingl
2019-06-12 19:58 ` [PATCH v3 02/14] pwm: meson: use devm_clk_get_optional() to get the input clock Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 03/14] pwm: meson: use GENMASK and FIELD_PREP for the lo and hi values Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 04/14] pwm: meson: change MISC_CLK_SEL_WIDTH to MISC_CLK_SEL_MASK Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 05/14] pwm: meson: don't duplicate the polarity internally Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 06/14] pwm: meson: pass struct pwm_device to meson_pwm_calc() Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 07/14] pwm: meson: add the meson_pwm_channel data to struct meson_pwm Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 08/14] pwm: meson: add the per-channel register offsets and bits in a struct Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 09/14] pwm: meson: move pwm_set_chip_data() to meson_pwm_request() Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 10/14] pwm: meson: simplify the calculation of the pre-divider and count Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 11/14] pwm: meson: read the full hardware state in meson_pwm_get_state() Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 12/14] pwm: meson: don't cache struct pwm_state internally Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 13/14] pwm: meson: add support PWM_POLARITY_INVERSED when disabling Martin Blumenstingl
2019-06-12 19:59 ` Martin Blumenstingl [this message]

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