Add a gpclk overlay (and a -pi5 variant) - #7601
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Add clk-hog, a trivial device-tree-only driver modelled on the gpio-hog concept: a node that just claims a set of clocks (configuring them via the standard assigned-clocks properties) and holds them prepared/enabled for as long as the node is bound, with no other consumer required. Assisted-by: Claude:claude-opus-5 Signed-off-by: Phil Elwell <phil@raspberrypi.com>
Enable building the clk-hog driver as a module. Signed-off-by: Phil Elwell <phil@raspberrypi.com>
Add a generic overlay for routing a GPCLK output onto a GPIO pin and setting its rate: gpclk for the BCM2835 GP0/GP1/GP2 clocks, and its Pi 5 counterpart gpclk-pi5 for the RP1 GP0-GP5 clocks, selected automatically via overlay_map.dts. Both overlays hold their clock open with a clk-hog device, so it stays enabled for as long as the overlay is loaded, with no other consumer required. Every legal pin+clock combination is also exposed as its own named override (gpclk0_4, gpclk0_20, gpclk1_5, ...), which sets the pin mux and clock index together in one go. The RP1 pinctrl driver accepts the same legacy numeric brcm,pins/brcm,function declarations as pinctrl-bcm2835, so gpclk-pi5 is written the same way and shares override names with gpclk for every combination the two chips have in common - a line such as "dtoverlay=gpclk,gpclk0_20" has the same effect on any Pi. RP1's extra GPCLK3-GPCLK5, and pins with no equivalent BCM283x ALT function, are exposed the same way but only exist in gpclk-pi5. Assisted-by: Claude:claude-opus-5 Signed-off-by: Phil Elwell <phil@raspberrypi.com>
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Raspberry Pi devices support enabling a number of clocks on a number of GPIO pins - these are called GPCLKs. These overlays allow these clocks to be configured from Device Tree. In order to get the clocks enabled, a fake consumer is required - hence the creation of the clk-hog driver.