gpiolib: allow simultaneous setting of multiple GPIO outputs

Introduce new functions gpiod_set_array & gpiod_set_raw_array to the consumer
interface which allow setting multiple outputs with just one function call.
Also add an optional set_multiple function to the driver interface. Without an
implementation of that function in the chip driver outputs are set
sequentially.

Implementing the set_multiple function in a chip driver allows for:
- Improved performance for certain use cases. The original motivation for this
  was the task of configuring an FPGA. In that specific case, where 9 GPIO
  lines have to be set many times, configuration time goes down from 48 s to
  20 s when using the new function.
- Simultaneous glitch-free setting of multiple pins on any kind of parallel
  bus attached to GPIOs provided they all reside on the same chip and bank.

Limitations:
  Performance is only improved for normal high-low outputs. Open drain and
  open source outputs are always set separately from each other. Those kinds
  of outputs could probably be accelerated in a similar way if we could
  forgo the error checking when setting GPIO directions.

Change log:
  v6: - rebase on current linux-gpio devel branch
  v5: - check can_sleep property per chip
      - remove superfluous checks
      - supplement documentation
  v4: - add gpiod_set_array function for setting logical values
      - change interface of the set_multiple driver function to use
        unsigned long as type for the bit fields
      - use generic bitops (which also use unsigned long for bit fields)
      - do not use ARCH_NR_GPIOS any more
  v3: - add documentation
      - change commit message
  v2: - use descriptor interface
      - allow arbitrary groups of GPIOs spanning multiple chips

Signed-off-by: Rojhalat Ibrahim <imr@rtschenk.de>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 168 insertions, 0 deletions

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 50e18a4b3a9f..eb739a51e774 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1254,6 +1254,88 @@ static void _gpiod_set_raw_value(struct gpio_desc *desc, bool value)
                 chip->set(chip, gpio_chip_hwgpio(desc), value);
 }
 
+/*
+ * set multiple outputs on the same chip;
+ * use the chip's set_multiple function if available;
+ * otherwise set the outputs sequentially;
+ * @mask: bit mask array; one bit per output; BITS_PER_LONG bits per word
+ *        defines which outputs are to be changed
+ * @bits: bit value array; one bit per output; BITS_PER_LONG bits per word
+ *        defines the values the outputs specified by mask are to be set to
+ */
+static void gpio_chip_set_multiple(struct gpio_chip *chip,
+                                   unsigned long *mask, unsigned long *bits)
+{
+        if (chip->set_multiple) {
+                chip->set_multiple(chip, mask, bits);
+        } else {
+                int i;
+                for (i = 0; i < chip->ngpio; i++) {
+                        if (mask[BIT_WORD(i)] == 0) {
+                                /* no more set bits in this mask word;
+                                 * skip ahead to the next word */
+                                i = (BIT_WORD(i) + 1) * BITS_PER_LONG - 1;
+                                continue;
+                        }
+                        /* set outputs if the corresponding mask bit is set */
+                        if (__test_and_clear_bit(i, mask)) {
+                                chip->set(chip, i, test_bit(i, bits));
+                        }
+                }
+        }
+}
+
+static void gpiod_set_array_priv(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]->chip;
+                unsigned long mask[BITS_TO_LONGS(chip->ngpio)];
+                unsigned long bits[BITS_TO_LONGS(chip->ngpio)];
+                int count = 0;
+
+                if (!can_sleep) {
+                        WARN_ON(chip->can_sleep);
+                }
+                memset(mask, 0, sizeof(mask));
+                do {
+                        struct gpio_desc *desc = desc_array[i];
+                        int hwgpio = gpio_chip_hwgpio(desc);
+                        int value = value_array[i];
+
+                        if (!raw && test_bit(FLAG_ACTIVE_LOW, &desc->flags))
+                                value = !value;
+                        trace_gpio_value(desc_to_gpio(desc), 0, value);
+                        /*
+                         * collect all normal outputs belonging to the same chip
+                         * open drain and open source outputs are set individually
+                         */
+                        if (test_bit(FLAG_OPEN_DRAIN, &desc->flags)) {
+                                _gpio_set_open_drain_value(desc,value);
+                        } else if (test_bit(FLAG_OPEN_SOURCE, &desc->flags)) {
+                                _gpio_set_open_source_value(desc, value);
+                        } else {
+                                __set_bit(hwgpio, mask);
+                                if (value) {
+                                        __set_bit(hwgpio, bits);
+                                } else {
+                                        __clear_bit(hwgpio, bits);
+                                }
+                                count++;
+                        }
+                        i++;
+                } while ((i < array_size) && (desc_array[i]->chip == chip));
+                /* push collected bits to outputs */
+                if (count != 0) {
+                        gpio_chip_set_multiple(chip, mask, bits);
+                }
+        }
+}
+
 /**
  * gpiod_set_raw_value() - assign a gpio's raw value
  * @desc: gpio whose value will be assigned
@@ -1299,6 +1381,48 @@ void gpiod_set_value(struct gpio_desc *desc, int value)
 EXPORT_SYMBOL_GPL(gpiod_set_value);
 
 /**
+ * gpiod_set_raw_array() - assign values to an array of GPIOs
+ * @array_size: number of elements in the descriptor / value arrays
+ * @desc_array: array of GPIO descriptors whose values will be assigned
+ * @value_array: array of values to assign
+ *
+ * Set the raw values of the GPIOs, i.e. the values of the physical lines
+ * without regard for their ACTIVE_LOW status.
+ *
+ * This function should be called from contexts where we cannot sleep, and will
+ * complain if the GPIO chip functions potentially sleep.
+ */
+void gpiod_set_raw_array(unsigned int array_size,
+                         struct gpio_desc **desc_array, int *value_array)
+{
+        if (!desc_array)
+                return;
+        gpiod_set_array_priv(true, false, array_size, desc_array, value_array);
+}
+EXPORT_SYMBOL_GPL(gpiod_set_raw_array);
+
+/**
+ * gpiod_set_array() - assign values to an array of GPIOs
+ * @array_size: number of elements in the descriptor / value arrays
+ * @desc_array: array of GPIO descriptors whose values will be assigned
+ * @value_array: array of values to assign
+ *
+ * Set the logical values of the GPIOs, i.e. taking their ACTIVE_LOW status
+ * into account.
+ *
+ * This function should be called from contexts where we cannot sleep, and will
+ * complain if the GPIO chip functions potentially sleep.
+ */
+void gpiod_set_array(unsigned int array_size,
+                     struct gpio_desc **desc_array, int *value_array)
+{
+        if (!desc_array)
+                return;
+        gpiod_set_array_priv(false, false, array_size, desc_array, value_array);
+}
+EXPORT_SYMBOL_GPL(gpiod_set_array);
+
+/**
  * gpiod_cansleep() - report whether gpio value access may sleep
  * @desc: gpio to check
  *
@@ -1458,6 +1582,50 @@ void gpiod_set_value_cansleep(struct gpio_desc *desc, int value)
 EXPORT_SYMBOL_GPL(gpiod_set_value_cansleep);
 
 /**
+ * gpiod_set_raw_array_cansleep() - assign values to an array of GPIOs
+ * @array_size: number of elements in the descriptor / value arrays
+ * @desc_array: array of GPIO descriptors whose values will be assigned
+ * @value_array: array of values to assign
+ *
+ * Set the raw values of the GPIOs, i.e. the values of the physical lines
+ * without regard for their ACTIVE_LOW status.
+ *
+ * This function is to be called from contexts that can sleep.
+ */
+void gpiod_set_raw_array_cansleep(unsigned int array_size,
+                                  struct gpio_desc **desc_array,
+                                  int *value_array)
+{
+        might_sleep_if(extra_checks);
+        if (!desc_array)
+                return;
+        gpiod_set_array_priv(true, true, array_size, desc_array, value_array);
+}
+EXPORT_SYMBOL_GPL(gpiod_set_raw_array_cansleep);
+
+/**
+ * gpiod_set_array_cansleep() - assign values to an array of GPIOs
+ * @array_size: number of elements in the descriptor / value arrays
+ * @desc_array: array of GPIO descriptors whose values will be assigned
+ * @value_array: array of values to assign
+ *
+ * Set the logical values of the GPIOs, i.e. taking their ACTIVE_LOW status
+ * into account.
+ *
+ * This function is to be called from contexts that can sleep.
+ */
+void gpiod_set_array_cansleep(unsigned int array_size,
+                              struct gpio_desc **desc_array,
+                              int *value_array)
+{
+        might_sleep_if(extra_checks);
+        if (!desc_array)
+                return;
+        gpiod_set_array_priv(false, true, array_size, desc_array, value_array);
+}
+EXPORT_SYMBOL_GPL(gpiod_set_array_cansleep);
+
+/**
  * gpiod_add_lookup_table() - register GPIO device consumers
  * @table: table of consumers to register
  */