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From: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
To: Linus Walleij <linus.walleij@linaro.org>,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Frank Rowand <frowand.list@gmail.com>
Cc: linux-gpio@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	"Jan Kundrát" <jan.kundrat@cesnet.cz>,
	"Thomas Petazzoni" <thomas.petazzoni@bootlin.com>
Subject: [PATCH v2 1/5] dt-bindings: gpio: document the new pull-up/pull-down flags
Date: Thu,  7 Feb 2019 17:28:55 +0100	[thread overview]
Message-ID: <20190207162859.26252-2-thomas.petazzoni@bootlin.com> (raw)
In-Reply-To: <20190207162859.26252-1-thomas.petazzoni@bootlin.com>

This commit extends the flags that can be used in GPIO specifiers to
indicate if a pull-up resistor or pull-down resistor should be
enabled.

While some pinctrl DT bindings already offer the capability of
configuring pull-up/pull-down resistors at the pin level, a number of
simple GPIO controllers don't have any pinmuxing capability, and
therefore do not rely on the pinctrl DT bindings.

Such simple GPIO controllers however sometimes allow to configure
pull-up and pull-down resistors on a per-pin basis, and whether such
resistors should be enabled or not is a highly board-specific HW
characteristic.

By using two additional bits of the GPIO flag specifier, we can easily
allow the Device Tree to describe which GPIOs should have their
pull-up or pull-down resistors enabled. Even though the two options
are mutually exclusive, we still need two bits to encode at least
three states: no pull-up/pull-down, pull-up, pull-down.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
---
 Documentation/devicetree/bindings/gpio/gpio.txt | 12 ++++++++++++
 include/dt-bindings/gpio/gpio.h                 |  6 ++++++
 2 files changed, 18 insertions(+)

diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt
index f0ba154b5723..a8895d339bfe 100644
--- a/Documentation/devicetree/bindings/gpio/gpio.txt
+++ b/Documentation/devicetree/bindings/gpio/gpio.txt
@@ -67,6 +67,18 @@ Optional standard bitfield specifiers for the last cell:
            https://en.wikipedia.org/wiki/Open_collector
 - Bit 3: 0 means the output should be maintained during sleep/low-power mode
          1 means the output state can be lost during sleep/low-power mode
+- Bit 4: 0 means no pull-up resistor should be enabled
+         1 means a pull-up resistor should be enabled
+         This setting only applies to hardware with a simple on/off
+         control for pull-up configuration. If the hardware has more
+         elaborate pull-up configuration, it should be represented
+         using a pin control binding.
+- Bit 5: 0 means no pull-down resistor should be enabled
+         1 means a pull-down resistor should be enabled
+         This setting only applies to hardware with a simple on/off
+         control for pull-down configuration. If the hardware has more
+         elaborate pull-down configuration, it should be represented
+         using a pin control binding.
 
 1.1) GPIO specifier best practices
 ----------------------------------
diff --git a/include/dt-bindings/gpio/gpio.h b/include/dt-bindings/gpio/gpio.h
index 2cc10ae4bbb7..c029467e828b 100644
--- a/include/dt-bindings/gpio/gpio.h
+++ b/include/dt-bindings/gpio/gpio.h
@@ -33,4 +33,10 @@
 #define GPIO_PERSISTENT 0
 #define GPIO_TRANSITORY 8
 
+/* Bit 4 express pull up */
+#define GPIO_PULL_UP 16
+
+/* Bit 5 express pull down */
+#define GPIO_PULL_DOWN 32
+
 #endif
-- 
2.20.1


  reply	other threads:[~2019-02-07 16:29 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-07 16:28 [PATCH v2 0/5] gpio: add support for pull-up/pull-down configuration Thomas Petazzoni
2019-02-07 16:28 ` Thomas Petazzoni [this message]
2019-02-07 16:28 ` [PATCH v2 2/5] gpio: rename gpio_set_drive_single_ended() to gpio_set_config() Thomas Petazzoni
2019-02-07 16:28 ` [PATCH v2 3/5] gpio: use new gpio_set_config() helper in more places Thomas Petazzoni
2019-03-16  1:43   ` Guenter Roeck
2019-03-16 13:45     ` Thomas Petazzoni
2019-03-16 14:20       ` Guenter Roeck
2019-03-26 20:03       ` Guenter Roeck
2019-03-26 21:04         ` Thomas Petazzoni
2019-02-07 16:28 ` [PATCH v2 4/5] gpio: add core support for pull-up/pull-down configuration Thomas Petazzoni
2019-02-07 16:28 ` [PATCH v2 5/5] gpio: pca953x: add ->set_config implementation Thomas Petazzoni
2019-02-13  8:15 ` [PATCH v2 0/5] gpio: add support for pull-up/pull-down configuration Linus Walleij

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