Some electronics do not allow the data regsister to be read without corrupting the existing data on the port. It a quirk of the board design. e.g. I have a couple of boards where the electronics engineer decided to only use the chip select line, so no read/write signal is connected. This means that reading the address activates the chip select and drives the contents of the data bus to the port.This makes it impossible to read the last data written to the port. This solution is to use the existing shadow data register 'bgpio_data'. It can be used to return the last value written to the port by the read operation. This is enabled for a particular port using a new flag and a new device tree property "no-input" to allow it to be selected on a board by board basis. This means it will only effect hardware that requests it. Signed-off-by: Niall Leonard <nl250060@xxxxxxx> --- Changes in v2: - Description of change updated to clarify why it is needed. - Patches squashed as per request during review. - wd,mbl-gpio bindings updated to yaml format. - Link to v1: https://lore.kernel.org/r/20230126-gpio-mmio-fix-v1-0-8a20ce0e8275@xxxxxxx --- Niall Leonard (2): dt-bindings: improve wb,mbl-gpio binding documentation. gpio: mmio: Use new flag BGPIOF_NO_INPUT. .../devicetree/bindings/gpio/wd,mbl-gpio.txt | 38 ----------- .../devicetree/bindings/gpio/wd,mbl-gpio.yaml | 78 ++++++++++++++++++++++ drivers/gpio/gpio-mmio.c | 24 ++++++- include/linux/gpio/driver.h | 1 + 4 files changed, 100 insertions(+), 41 deletions(-) --- base-commit: 1b929c02afd37871d5afb9d498426f83432e71c2 change-id: 20230126-gpio-mmio-fix-1a69d03ec9e7 Best regards, -- Niall Leonard <nl250060@xxxxxxx>
