gpio: Introduce ->get_multiple callback

SPI-attached GPIO controllers typically read out all inputs in one go.
If callers desire the values of multipe inputs, ideally a single readout
should take place to return the desired values.  However the current
driver API only offers a ->get callback but no ->get_multiple (unlike
->set_multiple, which is present).  Thus, to read multiple inputs, a
full readout needs to be performed for every single value (barring
driver-internal caching), which is inefficient.

In fact, the lack of a ->get_multiple callback has been bemoaned
repeatedly by the gpio subsystem maintainer:
http://www.spinics.net/lists/linux-gpio/msg10571.html
http://www.spinics.net/lists/devicetree/msg121734.html

Introduce the missing callback.  Add corresponding consumer functions
such as gpiod_get_array_value().  Amend linehandle_ioctl() to take
advantage of the newly added infrastructure.  Update the documentation.

Cc: Rojhalat Ibrahim <imr@rtschenk.de>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

2 files changed, 172 insertions, 11 deletions

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 8113929eb2bd..ff46a1b6299e 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -365,28 +365,28 @@ static long linehandle_ioctl(struct file *filep, unsigned int cmd,
 	struct linehandle_state *lh = filep->private_data;
 	void __user *ip = (void __user *)arg;
 	struct gpiohandle_data ghd;
+	int vals[GPIOHANDLES_MAX];
 	int i;
 
 	if (cmd == GPIOHANDLE_GET_LINE_VALUES_IOCTL) {
-		int val;
+		/* TODO: check if descriptors are really input */
+		int ret = gpiod_get_array_value_complex(false,
+							true,
+							lh->numdescs,
+							lh->descs,
+							vals);
+		if (ret)
+			return ret;
 
 		memset(&ghd, 0, sizeof(ghd));
-
-		/* TODO: check if descriptors are really input */
-		for (i = 0; i < lh->numdescs; i++) {
-			val = gpiod_get_value_cansleep(lh->descs[i]);
-			if (val < 0)
-				return val;
-			ghd.values[i] = val;
-		}
+		for (i = 0; i < lh->numdescs; i++)
+			ghd.values[i] = vals[i];
 
 		if (copy_to_user(ip, &ghd, sizeof(ghd)))
 			return -EFAULT;
 
 		return 0;
 	} else if (cmd == GPIOHANDLE_SET_LINE_VALUES_IOCTL) {
-		int vals[GPIOHANDLES_MAX];
-
 		/* TODO: check if descriptors are really output */
 		if (copy_from_user(&ghd, ip, sizeof(ghd)))
 			return -EFAULT;
@@ -2466,6 +2466,71 @@ static int gpiod_get_raw_value_commit(const struct gpio_desc *desc)
 	return value;
 }
 
+static int gpio_chip_get_multiple(struct gpio_chip *chip,
+				  unsigned long *mask, unsigned long *bits)
+{
+	if (chip->get_multiple) {
+		return chip->get_multiple(chip, mask, bits);
+	} else if (chip->get) {
+		int i, value;
+
+		for_each_set_bit(i, mask, chip->ngpio) {
+			value = chip->get(chip, i);
+			if (value < 0)
+				return value;
+			__assign_bit(i, bits, value);
+		}
+		return 0;
+	}
+	return -EIO;
+}
+
+int gpiod_get_array_value_complex(bool raw, bool can_sleep,
+				  unsigned int array_size,
+				  struct gpio_desc **desc_array,
+				  int *value_array)
+{
+	int i = 0;
+
+	while (i < array_size) {
+		struct gpio_chip *chip = desc_array[i]->gdev->chip;
+		unsigned long mask[BITS_TO_LONGS(chip->ngpio)];
+		unsigned long bits[BITS_TO_LONGS(chip->ngpio)];
+		int first, j, ret;
+
+		if (!can_sleep)
+			WARN_ON(chip->can_sleep);
+
+		/* collect all inputs belonging to the same chip */
+		first = i;
+		memset(mask, 0, sizeof(mask));
+		do {
+			const struct gpio_desc *desc = desc_array[i];
+			int hwgpio = gpio_chip_hwgpio(desc);
+
+			__set_bit(hwgpio, mask);
+			i++;
+		} while ((i < array_size) &&
+			 (desc_array[i]->gdev->chip == chip));
+
+		ret = gpio_chip_get_multiple(chip, mask, bits);
+		if (ret)
+			return ret;
+
+		for (j = first; j < i; j++) {
+			const struct gpio_desc *desc = desc_array[j];
+			int hwgpio = gpio_chip_hwgpio(desc);
+			int value = test_bit(hwgpio, bits);
+
+			if (!raw && test_bit(FLAG_ACTIVE_LOW, &desc->flags))
+				value = !value;
+			value_array[j] = value;
+			trace_gpio_value(desc_to_gpio(desc), 1, value);
+		}
+	}
+	return 0;
+}
+
 /**
  * gpiod_get_raw_value() - return a gpio's raw value
  * @desc: gpio whose value will be returned
@@ -2514,6 +2579,51 @@ int gpiod_get_value(const struct gpio_desc *desc)
 }
 EXPORT_SYMBOL_GPL(gpiod_get_value);
 
+/**
+ * gpiod_get_raw_array_value() - read raw values from an array of GPIOs
+ * @array_size: number of elements in the descriptor / value arrays
+ * @desc_array: array of GPIO descriptors whose values will be read
+ * @value_array: array to store the read values
+ *
+ * Read the raw values of the GPIOs, i.e. the values of the physical lines
+ * without regard for their ACTIVE_LOW status.  Return 0 in case of success,
+ * else an error code.
+ *
+ * This function should be called from contexts where we cannot sleep,
+ * and it will complain if the GPIO chip functions potentially sleep.
+ */
+int gpiod_get_raw_array_value(unsigned int array_size,
+			      struct gpio_desc **desc_array, int *value_array)
+{
+	if (!desc_array)
+		return -EINVAL;
+	return gpiod_get_array_value_complex(true, false, array_size,
+					     desc_array, value_array);
+}
+EXPORT_SYMBOL_GPL(gpiod_get_raw_array_value);
+
+/**
+ * gpiod_get_array_value() - read values from an array of GPIOs
+ * @array_size: number of elements in the descriptor / value arrays
+ * @desc_array: array of GPIO descriptors whose values will be read
+ * @value_array: array to store the read values
+ *
+ * Read the logical values of the GPIOs, i.e. taking their ACTIVE_LOW status
+ * into account.  Return 0 in case of success, else an error code.
+ *
+ * This function should be called from contexts where we cannot sleep,
+ * and it will complain if the GPIO chip functions potentially sleep.
+ */
+int gpiod_get_array_value(unsigned int array_size,
+			  struct gpio_desc **desc_array, int *value_array)
+{
+	if (!desc_array)
+		return -EINVAL;
+	return gpiod_get_array_value_complex(false, false, array_size,
+					     desc_array, value_array);
+}
+EXPORT_SYMBOL_GPL(gpiod_get_array_value);
+
 /*
  *  gpio_set_open_drain_value_commit() - Set the open drain gpio's value.
  * @desc: gpio descriptor whose state need to be set.
@@ -2943,6 +3053,53 @@ int gpiod_get_value_cansleep(const struct gpio_desc *desc)
 EXPORT_SYMBOL_GPL(gpiod_get_value_cansleep);
 
 /**
+ * gpiod_get_raw_array_value_cansleep() - read raw values from an array of GPIOs
+ * @array_size: number of elements in the descriptor / value arrays
+ * @desc_array: array of GPIO descriptors whose values will be read
+ * @value_array: array to store the read values
+ *
+ * Read the raw values of the GPIOs, i.e. the values of the physical lines
+ * without regard for their ACTIVE_LOW status.  Return 0 in case of success,
+ * else an error code.
+ *
+ * This function is to be called from contexts that can sleep.
+ */
+int gpiod_get_raw_array_value_cansleep(unsigned int array_size,
+				       struct gpio_desc **desc_array,
+				       int *value_array)
+{
+	might_sleep_if(extra_checks);
+	if (!desc_array)
+		return -EINVAL;
+	return gpiod_get_array_value_complex(true, true, array_size,
+					     desc_array, value_array);
+}
+EXPORT_SYMBOL_GPL(gpiod_get_raw_array_value_cansleep);
+
+/**
+ * gpiod_get_array_value_cansleep() - read values from an array of GPIOs
+ * @array_size: number of elements in the descriptor / value arrays
+ * @desc_array: array of GPIO descriptors whose values will be read
+ * @value_array: array to store the read values
+ *
+ * Read the logical values of the GPIOs, i.e. taking their ACTIVE_LOW status
+ * into account.  Return 0 in case of success, else an error code.
+ *
+ * This function is to be called from contexts that can sleep.
+ */
+int gpiod_get_array_value_cansleep(unsigned int array_size,
+				   struct gpio_desc **desc_array,
+				   int *value_array)
+{
+	might_sleep_if(extra_checks);
+	if (!desc_array)
+		return -EINVAL;
+	return gpiod_get_array_value_complex(false, true, array_size,
+					     desc_array, value_array);
+}
+EXPORT_SYMBOL_GPL(gpiod_get_array_value_cansleep);
+
+/**
  * gpiod_set_raw_value_cansleep() - assign a gpio's raw value
  * @desc: gpio whose value will be assigned
  * @value: value to assign
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index d003ccb12781..10a48caf8477 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -180,6 +180,10 @@ static inline bool acpi_can_fallback_to_crs(struct acpi_device *adev,
 #endif
 
 struct gpio_desc *gpiochip_get_desc(struct gpio_chip *chip, u16 hwnum);
+int gpiod_get_array_value_complex(bool raw, bool can_sleep,
+				  unsigned int array_size,
+				  struct gpio_desc **desc_array,
+				  int *value_array);
 void gpiod_set_array_value_complex(bool raw, bool can_sleep,
 				   unsigned int array_size,
 				   struct gpio_desc **desc_array,