diff options
Diffstat (limited to 'Documentation/driver-api/gpio/board.rst')
| -rw-r--r-- | Documentation/driver-api/gpio/board.rst | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/Documentation/driver-api/gpio/board.rst b/Documentation/driver-api/gpio/board.rst index 2c112553df84..a0f294e2e250 100644 --- a/Documentation/driver-api/gpio/board.rst +++ b/Documentation/driver-api/gpio/board.rst @@ -193,3 +193,27 @@ 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 array must meet the +following requirements: +- pin hardware number of array member 0 must also be 0, +- pin hardware numbers of consecutive array members which belong to the same + chip as member 0 does must also match their array indexes. + +Otherwise fast bitmap processing path is not used in order to avoid consecutive +pins which belong to the same chip but are not in hardware order being processed +separately. + +If the array applies for fast bitmap processing path, pins which belong to +different chips than member 0 does, as well as those with indexes different from +their hardware pin numbers, are excluded from the fast path, both input and +output. Moreover, open drain and open source pins are excluded from fast bitmap +output processing. |