[PATCH v4 16/16] gpio: Add a way to read 3-way strapping pins

[Simon Glass <sjg@chromium.org>]

Using the internal vs. external pull resistors it is possible to get
27 different combinations from 3 strapping pins. Add an implementation
of this.

This involves updating the sandbox GPIO driver to model external and
(weaker) internal pull resistors. The get_value() method now takes account
of what is driving a pin:

   sandbox: GPIOD_EXT_DRIVEN - in which case GPIO_EXT_HIGH provides the
          value
   outside source - in which case GPIO_EXT_PULL_UP/DOWN indicates the
          external state and we work the final state using those flags and
          the internal GPIOD_PULL_UP/DOWN flags

Of course the outside source does not really exist in sandbox. We are just
modelling it for test purpose.

Signed-off-by: Simon Glass <sjg@chromium.org>
---

(no changes since v3)

Changes in v3:
- Use bits 28, 29 for the new flags
- Assert that count parameter is within range
- Redo digit logic to be easier to understand
- Update function comment to explain the meaning of the digits
- Fix 'compare' typo

 arch/sandbox/include/asm/gpio.h |  5 +-
 drivers/gpio/gpio-uclass.c      | 81 +++++++++++++++++++++++++++
 drivers/gpio/sandbox.c          | 13 +++--
 include/asm-generic/gpio.h      | 40 ++++++++++++++
 test/dm/gpio.c                  | 98 +++++++++++++++++++++++++++++++++
 5 files changed, 232 insertions(+), 5 deletions(-)

diff --git a/arch/sandbox/include/asm/gpio.h b/arch/sandbox/include/asm/gpio.h
index 33b83ea4cc3..9e10052667d 100644
--- a/arch/sandbox/include/asm/gpio.h
+++ b/arch/sandbox/include/asm/gpio.h
@@ -26,8 +26,11 @@
 /* Our own private GPIO flags, which musn't conflict with GPIOD_... */
 #define GPIOD_EXT_HIGH		BIT(31)	/* external source is high (else low) */
 #define GPIOD_EXT_DRIVEN	BIT(30)	/* external source is driven */
+#define GPIOD_EXT_PULL_UP	BIT(29)	/* GPIO has external pull-up */
+#define GPIOD_EXT_PULL_DOWN	BIT(28)	/* GPIO has external pull-down */
 
-#define GPIOD_SANDBOX_MASK	GENMASK(31, 30)
+#define GPIOD_EXT_PULL		(BIT(28) | BIT(29))
+#define GPIOD_SANDBOX_MASK	GENMASK(31, 28)
 
 /**
  * Return the simulated value of a GPIO (used only in sandbox test code)
diff --git a/drivers/gpio/gpio-uclass.c b/drivers/gpio/gpio-uclass.c
index 308e75a1476..8dc647dc9f8 100644
--- a/drivers/gpio/gpio-uclass.c
+++ b/drivers/gpio/gpio-uclass.c
@@ -22,6 +22,7 @@
 #include <dm/device_compat.h>
 #include <linux/bug.h>
 #include <linux/ctype.h>
+#include <linux/delay.h>
 
 DECLARE_GLOBAL_DATA_PTR;
 
@@ -711,6 +712,21 @@ int dm_gpio_set_dir_flags(struct gpio_desc *desc, ulong flags)
 	return dm_gpio_clrset_flags(desc, GPIOD_MASK_DIR, flags);
 }
 
+int dm_gpios_clrset_flags(struct gpio_desc *desc, int count, ulong clr,
+			  ulong set)
+{
+	int ret;
+	int i;
+
+	for (i = 0; i < count; i++) {
+		ret = dm_gpio_clrset_flags(&desc[i], clr, set);
+		if (ret)
+			return log_ret(ret);
+	}
+
+	return 0;
+}
+
 int dm_gpio_get_flags(struct gpio_desc *desc, ulong *flagsp)
 {
 	struct udevice *dev = desc->dev;
@@ -977,6 +993,71 @@ int dm_gpio_get_values_as_int(const struct gpio_desc *desc_list, int count)
 	return vector;
 }
 
+int dm_gpio_get_values_as_int_base3(struct gpio_desc *desc_list,
+				    int count)
+{
+	static const char tristate[] = "01z";
+	enum {
+		PULLUP,
+		PULLDOWN,
+
+		NUM_OPTIONS,
+	};
+	int vals[NUM_OPTIONS];
+	uint mask;
+	uint vector = 0;
+	int ret, i;
+
+	/*
+	 * Limit to 19 digits which should be plenty. This avoids overflow of a
+	 * 32-bit int
+	 */
+	assert(count < 20);
+
+	for (i = 0; i < NUM_OPTIONS; i++) {
+		uint flags = GPIOD_IS_IN;
+
+		flags |= (i == PULLDOWN) ? GPIOD_PULL_DOWN : GPIOD_PULL_UP;
+		ret = dm_gpios_clrset_flags(desc_list, count, GPIOD_MASK_PULL,
+					    flags);
+		if (ret)
+			return log_msg_ret("pu", ret);
+
+		/* Give the lines time to settle */
+		udelay(10);
+
+		ret = dm_gpio_get_values_as_int(desc_list, count);
+		if (ret < 0)
+			return log_msg_ret("get1", ret);
+		vals[i] = ret;
+	}
+
+	log_debug("values: %x %x, count = %d\n", vals[0], vals[1], count);
+	for (i = count - 1, mask = 1 << i; i >= 0; i--, mask >>= 1) {
+		uint pd = vals[PULLDOWN] & mask ? 1 : 0;
+		uint pu = vals[PULLUP] & mask ? 1 : 0;
+		uint digit;
+
+		/*
+		 * Get value with internal pulldown active. If this is 1 then
+		 * there is a stronger external pullup, which we call 1. If not
+		 * then call it 0.
+		 *
+		 * If the values differ then the pin is floating so we call
+		 * this a 2.
+		 */
+		if (pu == pd)
+			digit = pd;
+		else
+			digit = 2;
+		log_debug("%c ", tristate[digit]);
+		vector = 3 * vector + digit;
+	}
+	log_debug("vector=%d\n", vector);
+
+	return vector;
+}
+
 /**
  * gpio_request_tail: common work for requesting a gpio.
  *
diff --git a/drivers/gpio/sandbox.c b/drivers/gpio/sandbox.c
index 700098446b5..d008fdd2224 100644
--- a/drivers/gpio/sandbox.c
+++ b/drivers/gpio/sandbox.c
@@ -19,7 +19,6 @@
 #include <dt-bindings/gpio/gpio.h>
 #include <dt-bindings/gpio/sandbox-gpio.h>
 
-
 struct gpio_state {
 	const char *label;	/* label given by requester */
 	ulong flags;		/* flags (GPIOD_...) */
@@ -81,10 +80,16 @@ int sandbox_gpio_get_value(struct udevice *dev, unsigned offset)
 	if (get_gpio_flag(dev, offset, GPIOD_IS_OUT))
 		debug("sandbox_gpio: get_value on output gpio %u\n", offset);
 
-	if (state->flags & GPIOD_EXT_DRIVEN)
+	if (state->flags & GPIOD_EXT_DRIVEN) {
 		val = state->flags & GPIOD_EXT_HIGH;
-	else
-		val = false;
+	} else {
+		if (state->flags & GPIOD_EXT_PULL_UP)
+			val = true;
+		else if (state->flags & GPIOD_EXT_PULL_DOWN)
+			val = false;
+		else
+			val = state->flags & GPIOD_PULL_UP;
+	}
 
 	return val;
 }
diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index 457ecb19cd3..e33cde7abdd 100644
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -497,6 +497,31 @@ int gpio_get_values_as_int(const int *gpio_list);
  */
 int dm_gpio_get_values_as_int(const struct gpio_desc *desc_list, int count);
 
+/**
+ * dm_gpio_get_values_as_int_base3() - Create a base-3 int from a list of GPIOs
+ *
+ * This uses pull-ups/pull-downs to figure out whether a GPIO line is externally
+ * pulled down, pulled up or floating. This allows three different strap values
+ * for each pin:
+ *    0 : external pull-down
+ *    1 : external pull-up
+ *    2 : floating
+ *
+ * With this it is possible to obtain more combinations from the same number of
+ * strapping pins, when compared to dm_gpio_get_values_as_int(). The external
+ * pull resistors should be made stronger that the internal SoC pull resistors,
+ * for this to work.
+ *
+ * With 2 pins, 6 combinations are possible, compared with 4
+ * With 3 pins, 27 are possible, compared with 8
+ *
+ * @desc_list: List of GPIOs to collect
+ * @count: Number of GPIOs
+ * @return resulting integer value, or -ve on error
+ */
+int dm_gpio_get_values_as_int_base3(struct gpio_desc *desc_list,
+				    int count);
+
 /**
  * gpio_claim_vector() - claim a number of GPIOs for input
  *
@@ -714,6 +739,21 @@ int dm_gpio_clrset_flags(struct gpio_desc *desc, ulong clr, ulong set);
  */
 int dm_gpio_set_dir_flags(struct gpio_desc *desc, ulong flags);
 
+/**
+ * dm_gpios_clrset_flags() - Sets flags for a set of GPIOs
+ *
+ * This clears and sets flags individually for each GPIO.
+ *
+ * @desc:	List of GPIOs to update
+ * @count:	Number of GPIOs in the list
+ * @clr:	Flags to clear (GPIOD_...), e.g. GPIOD_MASK_DIR if you are
+ *		changing the direction
+ * @set:	Flags to set (GPIOD_...)
+ * @return 0 if OK, -ve on error
+ */
+int dm_gpios_clrset_flags(struct gpio_desc *desc, int count, ulong clr,
+			  ulong set);
+
 /**
  * dm_gpio_get_flags() - Get flags
  *
diff --git a/test/dm/gpio.c b/test/dm/gpio.c
index be5da953045..33ae98701f4 100644
--- a/test/dm/gpio.c
+++ b/test/dm/gpio.c
@@ -680,3 +680,101 @@ static int dm_test_clrset_flags_invert(struct unit_test_state *uts)
 	return 0;
 }
 DM_TEST(dm_test_clrset_flags_invert, UT_TESTF_SCAN_PDATA | UT_TESTF_SCAN_FDT);
+
+static int set_gpios(struct unit_test_state *uts, struct gpio_desc *desc,
+		     int count, uint value)
+{
+	int i;
+
+	for (i = 0; i < count; i++) {
+		const uint mask = 1 << i;
+
+		ut_assertok(sandbox_gpio_set_value(desc[i].dev, desc[i].offset,
+						   value & mask));
+	}
+
+	return 0;
+}
+
+/* Check that an active-low GPIO works as expected */
+static int dm_test_gpio_get_values_as_int(struct unit_test_state *uts)
+{
+	const int gpio_count = 3;
+	struct gpio_desc desc[gpio_count];
+	struct udevice *dev;
+
+	ut_assertok(uclass_get_device(UCLASS_TEST_FDT, 0, &dev));
+	ut_asserteq_str("a-test", dev->name);
+
+	ut_asserteq(3, gpio_request_list_by_name(dev, "test-gpios", desc,
+						 gpio_count, GPIOD_IS_IN));
+	ut_assertok(set_gpios(uts, desc, gpio_count, 0));
+	ut_asserteq(0, dm_gpio_get_values_as_int(desc, gpio_count));
+
+	ut_assertok(set_gpios(uts, desc, gpio_count, 5));
+	ut_asserteq(5, dm_gpio_get_values_as_int(desc, gpio_count));
+
+	ut_assertok(set_gpios(uts, desc, gpio_count, 7));
+	ut_asserteq(7, dm_gpio_get_values_as_int(desc, gpio_count));
+
+	return 0;
+}
+DM_TEST(dm_test_gpio_get_values_as_int,
+	UT_TESTF_SCAN_PDATA | UT_TESTF_SCAN_FDT);
+
+/* Check that an active-low GPIO works as expected */
+static int dm_test_gpio_get_values_as_int_base3(struct unit_test_state *uts)
+{
+	const int gpio_count = 3;
+	struct gpio_desc desc[gpio_count];
+	struct udevice *dev;
+
+	ut_assertok(uclass_get_device(UCLASS_TEST_FDT, 0, &dev));
+	ut_asserteq_str("a-test", dev->name);
+
+	ut_asserteq(3, gpio_request_list_by_name(dev, "test-gpios", desc,
+						 gpio_count, GPIOD_IS_IN));
+
+	/*
+	 * First test the sandbox GPIO driver works as expected. The external
+	 * pull resistor should be stronger than the internal one.
+	 */
+	sandbox_gpio_set_flags(desc[0].dev, desc[0].offset,
+			       GPIOD_IS_IN | GPIOD_EXT_PULL_UP | GPIOD_PULL_UP);
+	ut_asserteq(1, dm_gpio_get_value(desc));
+
+	sandbox_gpio_set_flags(desc[0].dev, desc[0].offset, GPIOD_IS_IN |
+			       GPIOD_EXT_PULL_DOWN | GPIOD_PULL_UP);
+	ut_asserteq(0, dm_gpio_get_value(desc));
+
+	sandbox_gpio_set_flags(desc[0].dev, desc[0].offset,
+			       GPIOD_IS_IN | GPIOD_PULL_UP);
+	ut_asserteq(1, dm_gpio_get_value(desc));
+
+	sandbox_gpio_set_flags(desc[0].dev, desc[0].offset, GPIOD_PULL_DOWN);
+	ut_asserteq(0, dm_gpio_get_value(desc));
+
+	/*
+	 * Set up pins: pull-up (1), pull-down (0) and floating (2). This should
+	 * result in digits 2 0 1, i.e. 2 * 9 + 1 * 3 = 19
+	 */
+	sandbox_gpio_set_flags(desc[0].dev, desc[0].offset, GPIOD_EXT_PULL_UP);
+	sandbox_gpio_set_flags(desc[1].dev, desc[1].offset,
+			       GPIOD_EXT_PULL_DOWN);
+	sandbox_gpio_set_flags(desc[2].dev, desc[2].offset, 0);
+	ut_asserteq(19, dm_gpio_get_values_as_int_base3(desc, gpio_count));
+
+	/*
+	 * Set up pins: floating (2), pull-up (1) and pull-down (0). This should
+	 * result in digits 0 1 2, i.e. 1 * 3 + 2 = 5
+	 */
+	sandbox_gpio_set_flags(desc[0].dev, desc[0].offset, 0);
+	sandbox_gpio_set_flags(desc[1].dev, desc[1].offset, GPIOD_EXT_PULL_UP);
+	sandbox_gpio_set_flags(desc[2].dev, desc[2].offset,
+			       GPIOD_EXT_PULL_DOWN);
+	ut_asserteq(5, dm_gpio_get_values_as_int_base3(desc, gpio_count));
+
+	return 0;
+}
+DM_TEST(dm_test_gpio_get_values_as_int_base3,
+	UT_TESTF_SCAN_PDATA | UT_TESTF_SCAN_FDT);
-- 
2.30.0.478.g8a0d178c01-goog