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authorJulius Werner <jwerner@chromium.org>2014-09-24 15:40:49 -0700
committerPatrick Georgi <pgeorgi@google.com>2015-04-10 11:57:44 +0200
commit886d29bcd808476e0e83f68e3f7905fba4304b0a (patch)
treebb77525bc88e1cbc2bd35737bd5441e36e691507 /src/include/gpio.h
parenteaa9c4596b083ee1d1a48c5e7632abdb5b7e5297 (diff)
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gpio: Remove non-ternary tristate mode, make ternaries easier
The function to read board IDs from tristate GPIOs currently supports two output modes: a normal base-3 integer, or a custom format where every two bits represent one tristate pin. Each board decides which representation to use on its own, which is inconsistent and provides another possible gotcha to trip over when reading unfamiliar code. The two-bits-per-pin format creates the additional problem that a complete list of IDs (such as some boards use to build board-ID tables) necessarily has "holes" in them (since 0b11 does not correspond to a possible pin state), which makes them extremely tricky to write, read and expand. It's also very unintuitive in my opinion, although it was intended to make it easier to read individual pin states from a hex representation. This patch switches all boards over to base-3 and removes the other format to improve consistency. The tristate reading function will just print the pin states as they are read to make it easier to debug them, and we add a new BASE3() macro that can generate ternary numbers from pin states. Also change the order of all static initializers of board ID pin lists to write the most significant bit first, hoping that this can help clear up confusion about the endianness of the pins. CQ-DEPEND=CL:219902 BUG=None TEST=Booted on a Nyan_Blaze (with board ID 1, unfortunately the only one I have). Compiled on Daisy, Peach_Pit, Nyan, Nyan_Big, Nyan_Blaze, Rush, Rush_Ryu, Storm, Veryon_Pinky and Falco for good measure. Change-Id: I3ce5a0829f260db7d7df77e6788c2c6d13901b8f Signed-off-by: Patrick Georgi <pgeorgi@chromium.org> Original-Commit-Id: 2fa9545ac431c9af111ee4444d593ee4cf49554d Original-Change-Id: I6133cdaf01ed6590ae07e88d9e85a33dc013211a Original-Signed-off-by: Julius Werner <jwerner@chromium.org> Original-Reviewed-on: https://chromium-review.googlesource.com/219901 Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org> Reviewed-on: http://review.coreboot.org/9401 Tested-by: build bot (Jenkins) Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Diffstat (limited to 'src/include/gpio.h')
-rw-r--r--src/include/gpio.h14
1 files changed, 5 insertions, 9 deletions
diff --git a/src/include/gpio.h b/src/include/gpio.h
index af066970500e..b2a341dabcde 100644
--- a/src/include/gpio.h
+++ b/src/include/gpio.h
@@ -36,17 +36,13 @@ void gpio_output(gpio_t gpio, int value);
/*
* Read the value presented by the set of GPIOs, when each pin is interpreted
- * as a number in 0..2 range depending on the external pullup situation.
+ * as a base-3 digit (LOW = 0, HIGH = 1, Z/floating = 2).
+ * Example: X1 = Z, X2 = 1 -> gpio_get_tristates({GPIO(X1), GPIO(X2)}) = 5
+ * BASE3() from <base3.h> can generate numbers to compare the result to.
*
- * Depending on the third parameter, the return value is either a set of two
- * bit fields, each representing one GPIO value, or a number where each GPIO is
- * included multiplied by 3^gpio_num, resulting in a true tertiary value.
- *
- * gpio[]: pin positions to read. little-endian (less significant value first).
+ * gpio[]: pin positions to read. gpio[0] is less significant than gpio[1].
* num_gpio: number of pins to read.
- * tertiary: 1: pins are interpreted as a quad coded tertiary.
- * 0: pins are interpreted as a set of two bit fields.
*/
-int gpio_get_tristates(gpio_t gpio[], int num_gpio, int tertiary);
+int gpio_get_tristates(gpio_t gpio[], int num_gpio);
#endif /* __SRC_INCLUDE_GPIO_H__ */