path: root/Documentation/driver-api
diff options
authorJanusz Krzysztofik <jmkrzyszt@gmail.com>2018-09-05 23:50:08 +0200
committerLinus Walleij <linus.walleij@linaro.org>2018-09-13 11:17:23 +0200
commitb17566a6b08be18ded5472a2e4bbc066593b3662 (patch)
tree855c1933616c99b7b7998be6e5e5a88dc490d5a4 /Documentation/driver-api
parent77588c14ac868caece82fddbfae7de03b2cec941 (diff)
gpiolib: Implement fast processing path in get/set array
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> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Diffstat (limited to 'Documentation/driver-api')
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