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Properly support the GPIO_PIN_PRESET_{LOW,HIGH} options when configuring

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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.
This commit is contained in:
Ian Lepore 2018-05-04 19:28:05 +00:00
parent 8fd222ebb4
commit d8cf9c4f8b
1 changed files with 25 additions and 5 deletions
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30
sys/arm/freescale/imx/imx_gpio.c
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@ -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_pin, uint32_t clear_pins,
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_pin, uint32_t num_pins,
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;