Author: ian
Date: Thu Apr 7 19:51:27 2016
New Revision: 297684
URL: https://svnweb.freebsd.org/changeset/base/297684
Log:
Remove unecessary locking, mostly from places where a read is done of a
value that can't ever be in an inconsistant intermediate state even when
some other thread is in the middle of writing the value/register.
Locking of the hardware remains in the few places that do r-m-w operations.
Locking of metadata access is restricted to places using memcpy or sprintf
to modify the metadata.
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 Thu Apr 7 19:17:47 2016
(r297683)
+++ head/sys/arm/freescale/imx/imx_gpio.c Thu Apr 7 19:51:27 2016
(r297684)
@@ -451,22 +451,27 @@ static void
imx51_gpio_pin_configure(struct imx51_gpio_softc *sc, struct gpio_pin *pin,
unsigned int flags)
{
+ u_int newflags;
mtx_lock_spin(&sc->sc_mtx);
/*
- * Manage input/output
+ * Manage input/output; other flags not supported yet.
+ *
+ * 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.
*/
- if (flags & (GPIO_PIN_INPUT|GPIO_PIN_OUTPUT)) {
- pin->gp_flags &= ~(GPIO_PIN_INPUT|GPIO_PIN_OUTPUT);
+ if (flags & (GPIO_PIN_INPUT | GPIO_PIN_OUTPUT)) {
+ newflags = pin->gp_flags & ~(GPIO_PIN_INPUT | GPIO_PIN_OUTPUT);
if (flags & GPIO_PIN_OUTPUT) {
- pin->gp_flags |= GPIO_PIN_OUTPUT;
+ newflags |= GPIO_PIN_OUTPUT;
SET4(sc, IMX_GPIO_OE_REG, (1U << pin->gp_pin));
- }
- else {
- pin->gp_flags |= GPIO_PIN_INPUT;
+ } else {
+ newflags |= GPIO_PIN_INPUT;
CLEAR4(sc, IMX_GPIO_OE_REG, (1U << pin->gp_pin));
}
+ pin->gp_flags = newflags;
}
mtx_unlock_spin(&sc->sc_mtx);
@@ -503,9 +508,7 @@ imx51_gpio_pin_getcaps(device_t dev, uin
if (pin >= sc->gpio_npins)
return (EINVAL);
- mtx_lock_spin(&sc->sc_mtx);
*caps = sc->gpio_pins[pin].gp_caps;
- mtx_unlock_spin(&sc->sc_mtx);
return (0);
}
@@ -520,9 +523,7 @@ imx51_gpio_pin_getflags(device_t dev, ui
if (pin >= sc->gpio_npins)
return (EINVAL);
- mtx_lock_spin(&sc->sc_mtx);
*flags = sc->gpio_pins[pin].gp_flags;
- mtx_unlock_spin(&sc->sc_mtx);
return (0);
}
@@ -588,9 +589,7 @@ imx51_gpio_pin_get(device_t dev, uint32_
if (pin >= sc->gpio_npins)
return (EINVAL);
- mtx_lock_spin(&sc->sc_mtx);
*val = (READ4(sc, IMX_GPIO_DR_REG) >> pin) & 1;
- mtx_unlock_spin(&sc->sc_mtx);
return (0);
}
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