Change in coreboot[master]: lib/gpio.c: Fix _gpio_base3_value invalid shift

[Richard Spiegel (Code Review)]

Richard Spiegel has uploaded this change for review. ( https://review.coreboot.org/28445

Change subject: lib/gpio.c: Fix _gpio_base3_value invalid shift
......................................................................

lib/gpio.c: Fix _gpio_base3_value invalid shift

In function _gpio_base3_value(), if gpio_num is 32 and gpio[31] is floating,
the end result is 1 << 32, which does not fit into a int. To avoid a possible
error, in this condition set value to 0xffffffff.

Add a comment explaining why and the work around.

BUG=b:113788440
TEST=Add a fake code to southbridge_final calling the function and printing
the result. Build and boot grunt, check result.

Change-Id: I0b79725bcbaf120587c7440e176643aaa7a1d5bb
Signed-off-by: Richard Spiegel 
---
M src/lib/gpio.c
1 file changed, 13 insertions(+), 2 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/45/28445/1

diff --git a/src/lib/gpio.c b/src/lib/gpio.c
index da74849..4549166 100644
--- a/src/lib/gpio.c
+++ b/src/lib/gpio.c
@@ -75,7 +75,7 @@
     * internally pulled to.
     */

-	static const char tristate_char[] = {[0] = '0', [1] = '1', [Z] = 'Z'};
+	static const char tristate_char[] = {[0] = '0', [1] = '1', [2] = 'Z'};
    uint32_t result = 0;
    int has_z = 0;
    int binary_below = 0;
@@ -138,6 +138,14 @@
    	 * '2' at 3^1: Add 2^(1+1) = 4 to account for binaries 1000-1011
    	 * Stop adding for lower digits (3^0), all already accounted
    	 * now. We know that there can be no binary numbers 1020-102X.
+		 *
+		 * If gpio_num is 32 and gpio[31] is floating, the end result is
+		 * 1 << 32, which does not fit into a int. To avoid a possible
+		 * error, in this condition the value will be set to 0xffffffff.
+		 * There's a second condition which would set this value, to
+		 * have all inputs as 1. To differentiate between these results,
+		 * the caller needs to test if gpio[31] is floating. If gpio_num
+		 * is less than 32, no care is needed.
    	 */
    	if (binary_first && !has_z) {
    		switch (temp) {
@@ -147,7 +155,10 @@
    			binary_below += 1 << index;
    			break;
    		case 2:	/* Account for binaries 0 to 2^(index+1) - 1. */
-				binary_below += 1 << (index + 1);
+				if (index >= 31)
+					binary_below = 0xffffffff;
+				else
+					binary_below += 1 << (index + 1);
    			has_z = 1;
    		}
    	}