gpio: Add fast access to GPIO level

The current gpio_get_level() is pretty slow because it looks things up each
time. Add a new function to find out the register address and mask to use
to check the value for a particular GPIO.

Time-critical code can then use this to check a GPIO.

BUG=chrome-os-partner:10146
TEST=manual:
build and boot on snow;
Power on the board, hold power button for 10s and see that it powers off
Power control still works, thus GPIOs are functional

Change-Id: Ifc6c56f5cb811e0243e7712725a51948eabd42ab
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/26175

2 files changed, 19 insertions, 0 deletions

diff --git a/chip/stm32/gpio-stm32f100.c b/chip/stm32/gpio-stm32f100.c
index e1a28b8d7a..50c732bc27 100644
--- a/chip/stm32/gpio-stm32f100.c
+++ b/chip/stm32/gpio-stm32f100.c
@@ -174,6 +174,13 @@ void gpio_set_alternate_function(int port, int mask, int func)
 }
 
 
+uint16_t *gpio_get_level_reg(enum gpio_signal signal, uint32_t *mask)
+{
+	*mask = gpio_list[signal].mask;
+	return (uint16_t *)&STM32_GPIO_IDR_OFF(gpio_list[signal].port);
+}
+
+
 int gpio_get_level(enum gpio_signal signal)
 {
 	return !!(STM32_GPIO_IDR_OFF(gpio_list[signal].port) &
diff --git a/include/gpio.h b/include/gpio.h
index b70e40f9a1..e03acfb0c9 100644
--- a/include/gpio.h
+++ b/include/gpio.h
@@ -66,6 +66,18 @@ int gpio_pre_init(void);
 int gpio_get_level(enum gpio_signal signal);
 
 /**
+ * Get faster access to a GPIO level
+ *
+ * Use this function to find out the register address and mask for a GPIO
+ * value. Then you can just check that instead of calling gpio_get_level().
+ *
+ * @param signal	Signal to return details for
+ * @param mask		Mask value to use
+ * @return pointer to register to read to get GPIO value
+ */
+uint16_t *gpio_get_level_reg(enum gpio_signal signal, uint32_t *mask);
+
+/**
  * Returns the name of a given GPIO signal.
  *
  * @param signal	Signal to return.