diff options
Diffstat (limited to 'Documentation/driver-api')
| -rw-r--r-- | Documentation/driver-api/gpio/board.rst | 19 |
1 files changed, 14 insertions, 5 deletions
diff --git a/Documentation/driver-api/gpio/board.rst b/Documentation/driver-api/gpio/board.rst index c66821e033c2..a0f294e2e250 100644 --- a/Documentation/driver-api/gpio/board.rst +++ b/Documentation/driver-api/gpio/board.rst @@ -202,9 +202,18 @@ 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 +In order to qualify for fast bitmap processing, the array 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. +- 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. |