New patch to review for coreboot: gpio: Add support for extended binary number system

[David Hendricks]

David Hendricks ([e-mail]) just uploaded a new patch set to gerrit, which you can find at https://review.coreboot.org/14143

-gerrit

commit a759a4e137679da3a11587e3334b98443436d73d
Author: David Hendricks 
Date:   Fri Mar 18 20:23:05 2016 -0700

gpio: Add support for extended binary number system

This adds yet another number system which logically extends the binary
    representation to allow floating/high-Z values to count in the result.
    A 'Z' value at position N will yield a value of 0 at position N and a
    value of 1 at position (1 << N << num_gpio).
    For example:
    000Z => 0b1_0000
    100Z => 0b1_1000

BRANCH=none
    BUG=none
    TEST=stubbed out and tested for a 3-wide raw value, see comments
    in gerrit for the full table.

Change-Id: I121e0cac9fa84fcbb261d1d84dcb20cfd49e5518
    Signed-off-by: David Hendricks 
---
 src/include/gpio.h | 13 +++++++++++++
 src/lib/gpio.c     | 19 +++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/src/include/gpio.h b/src/include/gpio.h
index ea03a23..3b22154 100644
--- a/src/include/gpio.h
+++ b/src/include/gpio.h
@@ -41,6 +41,19 @@ int gpio_base2_value(gpio_t gpio[], int num_gpio);

/*
  * Read the value presented by the set of GPIOs, when each pin is interpreted
+ * as a base-2 digit (LOW = 0, HIGH = 1). If a pin is in its Z/floating state
+ * the value becomes (1 << pin_num << num_gpio).
+ *
+ * Caveat: This scheme makes the number space discontinuous. The advantage is
+ * that it's simple to compute and translate to/from hex.
+ *
+ * gpio[]: pin positions to read. gpio[0] is less significant than gpio[1].
+ * num_gpio: number of pins to read.
+ */
+int gpio_base2_ext_value(gpio_t gpio[], int num_gpio);
+
+/*
+ * Read the value presented by the set of GPIOs, when each pin is interpreted
  * as a base-3 digit (LOW = 0, HIGH = 1, Z/floating = 2).
  * Example: X1 = Z, X2 = 1 -> gpio_base3_value({GPIO(X1), GPIO(X2)}) = 5
  * BASE3() from <base3.h> can generate numbers to compare the result to.
diff --git a/src/lib/gpio.c b/src/lib/gpio.c
index 5147cfe..cfe1786 100644
--- a/src/lib/gpio.c
+++ b/src/lib/gpio.c
@@ -35,6 +35,25 @@ int gpio_base2_value(gpio_t gpio[], int num_gpio)
    return result;
 }

+int gpio_base2_ext_value(gpio_t gpio[], int num_gpio)
+{
+	static const char tristate_char[] = {[0] = '0', [1] = '1', [2] = 'Z'};
+	int temp, index, result = 0;
+
+	for (index = num_gpio - 1; index >= 0; --index) {
+		temp = gpio_get(gpio[index]);
+		printk(BIOS_DEBUG, "%c ", tristate_char[temp]);
+
+		if (temp == 2)	/* Z-state */
+			result += (1 << index << num_gpio);
+		else
+			result += temp * (1 << index);
+	}
+
+	printk(BIOS_DEBUG, "= 0x%x (extended binary number system)\n", result);
+	return result;
+}
+
 int gpio_base3_value(gpio_t gpio[], int num_gpio)
 {
    /*