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Date:      Fri, 4 May 2018 19:28:05 +0000 (UTC)
From:      Ian Lepore <ian@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r333260 - head/sys/arm/freescale/imx
Message-ID:  <201805041928.w44JS5vo094031@repo.freebsd.org>
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Author: ian
Date: Fri May  4 19:28:05 2018
New Revision: 333260
URL: https://svnweb.freebsd.org/changeset/base/333260

Log:
  Properly support the GPIO_PIN_PRESET_{LOW,HIGH} options when configuring
  a gpio pin.  If neither of the options is specified, pre-set the pin's
  output value to the pin's current input value, to achieve glitch-free
  transitions to output mode on pins that are pulled up or down at reset
  or via fdt pinctrl data.

Modified:
  head/sys/arm/freescale/imx/imx_gpio.c

Modified: head/sys/arm/freescale/imx/imx_gpio.c
==============================================================================
--- head/sys/arm/freescale/imx/imx_gpio.c	Fri May  4 18:59:01 2018	(r333259)
+++ head/sys/arm/freescale/imx/imx_gpio.c	Fri May  4 19:28:05 2018	(r333260)
@@ -506,21 +506,41 @@ static void
 imx51_gpio_pin_configure(struct imx51_gpio_softc *sc, struct gpio_pin *pin,
     unsigned int flags)
 {
-	u_int newflags;
+	u_int newflags, pad;
 
 	mtx_lock_spin(&sc->sc_mtx);
 
 	/*
-	 * Manage input/output; other flags not supported yet.
+	 * Manage input/output; other flags not supported yet (maybe not ever,
+	 * since we have no connection to the pad config registers from here).
 	 *
+	 * When setting a pin to output, honor the PRESET_[LOW,HIGH] flags if
+	 * present.  Otherwise, for glitchless transistions on pins with pulls,
+	 * read the current state of the pad and preset the DR register to drive
+	 * the current value onto the pin before enabling the pin for output.
+	 *
 	 * Note that changes to pin->gp_flags must be acccumulated in newflags
 	 * and stored with a single writeback to gp_flags at the end, to enable
-	 * unlocked reads of that value elsewhere.
+	 * unlocked reads of that value elsewhere. This is only about unlocked
+	 * access to gp_flags from elsewhere; we still use locking in this
+	 * function to protect r-m-w access to the hardware registers.
 	 */
 	if (flags & (GPIO_PIN_INPUT | GPIO_PIN_OUTPUT)) {
 		newflags = pin->gp_flags & ~(GPIO_PIN_INPUT | GPIO_PIN_OUTPUT);
 		if (flags & GPIO_PIN_OUTPUT) {
+			if (flags & GPIO_PIN_PRESET_LOW) {
+				pad = 0;
+			} else if (flags & GPIO_PIN_PRESET_HIGH) {
+				pad = 1;
+			} else {
+				if (flags & GPIO_PIN_OPENDRAIN)
+					pad = READ4(sc, IMX_GPIO_PSR_REG);
+				else
+					pad = READ4(sc, IMX_GPIO_DR_REG);
+				pad = (pad >> pin->gp_pin) & 1;
+			}
 			newflags |= GPIO_PIN_OUTPUT;
+			SET4(sc, IMX_GPIO_DR_REG, (pad << pin->gp_pin));
 			SET4(sc, IMX_GPIO_OE_REG, (1U << pin->gp_pin));
 		} else {
 			newflags |= GPIO_PIN_INPUT;
@@ -692,7 +712,7 @@ imx51_gpio_pin_access_32(device_t dev, uint32_t first_
 	sc = device_get_softc(dev);
 
 	if (orig_pins != NULL)
-		*orig_pins = READ4(sc, IMX_GPIO_PSR_REG);
+		*orig_pins = READ4(sc, IMX_GPIO_DR_REG);
 
 	if ((clear_pins | change_pins) != 0) {
 		mtx_lock_spin(&sc->sc_mtx);
@@ -718,7 +738,7 @@ imx51_gpio_pin_config_32(device_t dev, uint32_t first_
 		return (EINVAL);
 
 	drclr = drset = oeclr = oeset = 0;
-	pads = READ4(sc, IMX_GPIO_PSR_REG);
+	pads = READ4(sc, IMX_GPIO_DR_REG);
 
 	for (i = 0; i < num_pins; ++i) {
 		bit = 1u << i;

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