Hello everybody, While working on Dt support for a driver that uses GPIO I came to ponder about the correct meaning of the GPIO active low flag. I'm bringing the question to the mailing list to get feedback.
When a device has an active low input, the fact that the input is active low is a property of the device, and thus known to the driver. On the other hand, if an inverter is present on the board, that information isn't known to device drivers and need to be expressed in DT. Does the active low flag express the latter only, or both of them ? To ask the question differently, should the low flag model the inverter inside the device, known to the device driver, effectively moving handling of that inverter out of the device driver to the core code, or should it stop at the device boundary and only model the board ? As an example, if my device datasheet states that the reset input is active low, an no inverter is present on the GPIO line, should I set the GPIO active low flag in DT and set the GPIO value to 1 in software (assuming I use the gpiod_* API) to make the reset signal active, or should I set the GPIO active high flag in DT and the the GPIO value to 0 in software ? Let's also keep in mind that devices can have programmable polarities for inputs connected to GPIO-driven signals, in which case the internal polarity inversion is dynamic and can't be expressed in the GPIO propery in DT. -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-gpio" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
