[PATCH v7 4/4] gpiolib: Implement fast processing path in get/set array

Janusz Krzysztofik
2018-09-02T12:01:41Z

Certain GPIO descriptor arrays returned by gpio_get_array() may contain
information on direct mapping of array members to pins of a single GPIO
chip in hardware order. In such cases, bitmaps of values can be passed
directly from/to the chip's .get/set_multiple() callbacks without
wasting time on iterations.

Add respective code to gpiod_get/set_array_bitmap_complex() functions.
Pins not applicable for fast path are processed as before, skipping
over the 'fast' ones.

Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
---
Documentation/driver-api/gpio/board.rst | 15 ++++++
Documentation/driver-api/gpio/consumer.rst | 8 +++
drivers/gpio/gpiolib.c | 87 ++++++++++++++++++++++++++++--
3 files changed, 105 insertions(+), 5 deletions(-)

diff --git a/Documentation/driver-api/gpio/board.rst b/Documentation/driver-api/gpio/board.rst
index 2c112553df84..c66821e033c2 100644
--- a/Documentation/driver-api/gpio/board.rst
+++ b/Documentation/driver-api/gpio/board.rst
@@ -193,3 +193,18 @@ And the table can be added to the board code as follows::

The line will be hogged as soon as the gpiochip is created or - in case the
chip was created earlier - when the hog table is registered.
+
+Arrays of pins
+--------------
+In addition to requesting pins belonging to a function one by one, a device may
+also request an array of pins assigned to the function. The way those pins are
+mapped to the device determines if the array qualifies for fast bitmap
+processing. If yes, a bitmap is passed over get/set array functions directly
+between a caller and a respective .get/set_multiple() callback of a GPIO chip.
+
+In order to qualify for fast bitmap processing, the pin mapping must meet the
+following requirements:
+- it must belong to the same chip as other 'fast' pins of the function,
+- its index within the function must match its hardware number within the chip.
+
+Open drain and open source pins are excluded from fast bitmap output processing.
diff --git a/Documentation/driver-api/gpio/consumer.rst b/Documentation/driver-api/gpio/consumer.rst
index 0afd95a12b10..cf992e5ab976 100644
--- a/Documentation/driver-api/gpio/consumer.rst
+++ b/Documentation/driver-api/gpio/consumer.rst
@@ -388,6 +388,14 @@ array_info should be set to NULL.
Note that for optimal performance GPIOs belonging to the same chip should be
contiguous within the array of descriptors.

+Still better performance may be achieved if array indexes of the descriptors
+match hardware pin numbers of a single chip. If an array passed to a get/set
+array function matches the one obtained from gpiod_get_array() and array_info
+associated with the array is also passed, the function may take a fast bitmap
+processing path, passing the value_bitmap argument directly to the respective
+.get/set_multiple() callback of the chip. That allows for utilization of GPIO
+banks as data I/O ports without much loss of performance.
+
The return value of gpiod_get_array_value() and its variants is 0 on success
or negative on error. Note the difference to gpiod_get_value(), which returns
0 or 1 on success to convey the GPIO value. With the array functions, the GPIO
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index cef6ee31fe05..b9d083fb13ee 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2789,7 +2789,36 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep,
struct gpio_array *array_info,
unsigned long *value_bitmap)
{
- int i = 0;
+ int err, i = 0;
+
+ /*
+ * Validate array_info against desc_array and its size.
+ * It should immediately follow desc_array if both
+ * have been obtained from the same gpiod_get_array() call.
+ */
+ if (array_info && array_info->desc == desc_array &&
+ array_size <= array_info->size &&
+ (void *)array_info == desc_array + array_info->size) {
+ if (!can_sleep)
+ WARN_ON(array_info->chip->can_sleep);
+
+ err = gpio_chip_get_multiple(array_info->chip,
+ array_info->get_mask,
+ value_bitmap);
+ if (err)
+ return err;
+
+ if (!raw && !bitmap_empty(array_info->invert_mask, array_size))
+ bitmap_xor(value_bitmap, value_bitmap,
+ array_info->invert_mask, array_size);
+
+ if (bitmap_full(array_info->get_mask, array_size))
+ return 0;
+
+ i = find_first_zero_bit(array_info->get_mask, array_size);
+ } else {
+ array_info = NULL;
+ }

while (i < array_size) {
struct gpio_chip *chip = desc_array[i]->gdev->chip;
@@ -2820,7 +2849,12 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep,
int hwgpio = gpio_chip_hwgpio(desc);

__set_bit(hwgpio, mask);
- i++;
+
+ if (array_info)
+ find_next_zero_bit(array_info->get_mask,
+ array_size, i);
+ else
+ i++;
} while ((i < array_size) &&
(desc_array[i]->gdev->chip == chip));

@@ -2831,7 +2865,7 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep,
return ret;
}

- for (j = first; j < i; j++) {
+ for (j = first; j < i; ) {
const struct gpio_desc *desc = desc_array[j];
int hwgpio = gpio_chip_hwgpio(desc);
int value = test_bit(hwgpio, bits);
@@ -2840,6 +2874,11 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep,
value = !value;
__assign_bit(j, value_bitmap, value);
trace_gpio_value(desc_to_gpio(desc), 1, value);
+
+ if (array_info)
+ find_next_zero_bit(array_info->get_mask, i, j);
+ else
+ j++;
}

if (mask != fastpath)
@@ -3041,6 +3080,32 @@ int gpiod_set_array_value_complex(bool raw, bool can_sleep,
{
int i = 0;

+ /*
+ * Validate array_info against desc_array and its size.
+ * It should immediately follow desc_array if both
+ * have been obtained from the same gpiod_get_array() call.
+ */
+ if (array_info && array_info->desc == desc_array &&
+ array_size <= array_info->size &&
+ (void *)array_info == desc_array + array_info->size) {
+ if (!can_sleep)
+ WARN_ON(array_info->chip->can_sleep);
+
+ if (!raw && !bitmap_empty(array_info->invert_mask, array_size))
+ bitmap_xor(value_bitmap, value_bitmap,
+ array_info->invert_mask, array_size);
+
+ gpio_chip_set_multiple(array_info->chip, array_info->set_mask,
+ value_bitmap);
+
+ if (bitmap_full(array_info->set_mask, array_size))
+ return 0;
+
+ i = find_first_zero_bit(array_info->set_mask, array_size);
+ } else {
+ array_info = NULL;
+ }
+
while (i < array_size) {
struct gpio_chip *chip = desc_array[i]->gdev->chip;
unsigned long fastpath[2 * BITS_TO_LONGS(FASTPATH_NGPIO)];
@@ -3068,7 +3133,14 @@ int gpiod_set_array_value_complex(bool raw, bool can_sleep,
int hwgpio = gpio_chip_hwgpio(desc);
int value = test_bit(i, value_bitmap);

- if (!raw && test_bit(FLAG_ACTIVE_LOW, &desc->flags))
+ /*
+ * Pins applicable for fast input but not for
+ * fast output processing may have been already
+ * inverted inside the fast path, skip them.
+ */
+ if (!raw && !(array_info &&
+ test_bit(i, array_info->invert_mask)) &&
+ test_bit(FLAG_ACTIVE_LOW, &desc->flags))
value = !value;
trace_gpio_value(desc_to_gpio(desc), 0, value);
/*
@@ -3087,7 +3159,12 @@ int gpiod_set_array_value_complex(bool raw, bool can_sleep,
__clear_bit(hwgpio, bits);
count++;
}
- i++;
+
+ if (array_info)
+ find_next_zero_bit(array_info->set_mask,
+ array_size, i);
+ else
+ i++;
} while ((i < array_size) &&
(desc_array[i]->gdev->chip == chip));
/* push collected bits to outputs */
--
2.16.4