Allow GPIOs to be set up later

At present GPIOs must be staticly defined in a table. This is efficient
but inflexible, and requires error-prone and correponding #ifdefs both
in the board's gpio.h and gpio.c files.

Create a GPIO_UNSET option for GPIOs. This allows them to be assigned
an enum value, but have the actual use under program control.

BUG=chrome-os-partner:13064
BRANCH=snow,link
TEST=manual
build and boot on snow with later changes. See the AC power GPIO does
not change when un/plugging power.

Change-Id: Iab58275923d7d6cfce62c890b5db9b6758279a4c
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/31302
Reviewed-by: David Hendricks <dhendrix@chromium.org>

chip/lm4/gpio.c

@@ -180,6 +180,8 @@ int gpio_set_flags(enum gpio_signal signal, int flags)
 {
 	const struct gpio_info *g = gpio_list + signal;
 
+	if (flags & GPIO_DEFAULT)
+		return EC_SUCCESS;
 	if (flags & GPIO_OUTPUT) {
 		/* Output */
 		/* Select open drain first, so that we don't glitch the signal

chip/stm32/gpio-stm32f100.c

@@ -57,6 +57,8 @@ int gpio_set_flags(enum gpio_signal signal, int flags)
 	const struct gpio_info *g = gpio_list + signal;
 	uint32_t addr, cnf, mode, mask;
 
+	if (flags & GPIO_DEFAULT)
+		return EC_SUCCESS;
 	gpio_config_info(g, &addr, &mode, &cnf);
 	mask = REG32(addr) & ~(cnf | mode);
 

chip/stm32/gpio-stm32l15x.c

@@ -41,6 +41,8 @@ int gpio_pre_init(void)
 		uint32_t mask2 = (g->mask * g->mask) | (g->mask * g->mask * 2);
 		uint32_t val;
 
+		if (g->mask & GPIO_DEFAULT)
+			continue;
 		val = STM32_GPIO_PUPDR_OFF(g->port) & ~mask2;
 		if ((g->flags & GPIO_PULL_UP) == GPIO_PULL_UP)
 			/* Pull Up = 01 */

include/gpio.h

@@ -25,7 +25,7 @@
 #define GPIO_INT_BOTH    0x0040  /* Interrupt on both edges */
 #define GPIO_INT_LOW     0x0080  /* Interrupt on low level */
 #define GPIO_INT_HIGH    0x0100  /* Interrupt on high level */
-
+#define GPIO_DEFAULT     0x0200  /* Don't set up on boot */
 
 /* Common flag combinations */
 #define GPIO_OUT_LOW     GPIO_OUTPUT