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-rw-r--r--Documentation/driver-api/gpio/board.rst15
-rw-r--r--Documentation/driver-api/gpio/consumer.rst8
2 files changed, 23 insertions, 0 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