diff options
| author | Janusz Krzysztofik <jmkrzyszt@gmail.com> | 2018-09-06 00:50:08 +0300 |
|---|---|---|
| committer | Linus Walleij <linus.walleij@linaro.org> | 2018-09-13 12:17:23 +0300 |
| commit | b17566a6b08be18ded5472a2e4bbc066593b3662 (patch) | |
| tree | 855c1933616c99b7b7998be6e5e5a88dc490d5a4 /Documentation/driver-api | |
| parent | 77588c14ac868caece82fddbfae7de03b2cec941 (diff) | |
| download | linux-b17566a6b08be18ded5472a2e4bbc066593b3662.tar.xz | |
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')
| -rw-r--r-- | Documentation/driver-api/gpio/board.rst | 15 | ||||
| -rw-r--r-- | Documentation/driver-api/gpio/consumer.rst | 8 |
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 |