ASUS Transformers require this driver for proper work with their dock. Dock is controlled by EC and its presence is detected by a GPIO. The Transformers have a connector that's used for USB, charging or for attaching a keyboard (called a dock; it also has a battery and a touchpad). This connector probably (I don't have the means to verify that) has an I2C bus lines and a "detect" line (pulled low on the dock side) among the pins. I guess there is either no additional chip or a transparent bridge/buffer chip, but nothing that could be controlled by software. For DT this setup could be modelled like an I2C gate or a 2-port mux with enable joining two I2C buses (one "closer" to the CPU as a parent). In this case it's hard to tell the difference if this is real or virtual hardware. This patchset is a predecessor of a possible larger patchset which should bring support for a asus-ec, an i2c mfd device programmed by Asus for their Transformers tablet line. Similar approach is used in Microsoft Surface RT for attachable Type Cover. > What is this actually doing? Basically it duplicates the parent i2c bus once detection GPIO triggers and probes all hot-pluggable devices which are connected to it. Once GPIO triggers a detach signal all hot-pluggable devices are unprobed and bus removed. > Is the GPIO an irq line for signalling hoplugging and can be used by > any driver or just this one? It can be shared if necessary but usually all hot-pluggable devices are gathered in one container and are plugged simultaneously. --- Changes from v2: - expanded descryption of driver implementation commit - expanded descryption in patchset cover - no changes to code or yaml from v2 Changes from v1: - documentation changes: - dropped | from description - dropped nodename - unified use of quotes - used GPIO_ACTIVE_LOW define - used phandle instead of path --- Michał Mirosław (1): i2c: Add GPIO-based hotplug gate Svyatoslav Ryhel (1): dt-bindings: i2c: add binding for i2c-hotplug-gpio .../bindings/i2c/i2c-hotplug-gpio.yaml | 65 +++++ drivers/i2c/Kconfig | 11 + drivers/i2c/Makefile | 1 + drivers/i2c/i2c-hotplug-gpio.c | 266 ++++++++++++++++++ 4 files changed, 343 insertions(+) create mode 100644 Documentation/devicetree/bindings/i2c/i2c-hotplug-gpio.yaml create mode 100644 drivers/i2c/i2c-hotplug-gpio.c -- 2.39.2
