Mainline:Broadcom Kona/Pin control (PADCTRL)
The pin controller in the BCM21664/BCM23550 appears to be somewhat similar to BCM28155, judging by the mainline driver.
- BCM21664 has 155 pins; each pin can also have 6 functions.
- BCM28155 has 268 pins; each pin can also have 4 functions.
The downstream pinmux driver is located at arch/arm/plat-kona/pinmux.c, with per-platform settings defined in arch/arm/mach-{codename}/{codename}_pinmux.c. These files also contain the init function pinmux_chip_init(), which on Java and Hawaii does two things:
- unlocks the pinmux
- allocates the memory for the pinmux driver to use
The pin controller/pinmux API, as well as a general explaination of how a pin controller works, can be found in the kernel documentation here: https://www.kernel.org/doc/html/latest/driver-api/pin-control.html (ah, if every component had a piece of docs like this...)
Pin description
There are two ways in whicn pins are described in the downstream kernel (arch/arm/mach-{codename}/{codename}_pinmux.c):
- using PIN_CFG and PIN_BSC_CFG, as seen in rhea.
- using a custom
PIN_DESCshorthand, as seen in hawaii/java; this wraps aroundPIN_CFG.
Pins
There two types of pins: standard and I2C (BSC). BCM218XX driver in mainline also has a HDMI pin type.
Functions
Each pin can have 4 (BCM28155) or 6 (BCM2166x) alternative functions. The names (and thus numbers) for these are defined separately in the downstream drivers. They cover a lot more cases than just the base pins, including things like every GPIO. (This is a fairly standard pin muxing setup.)
The currently selected function is saved to the selector register, which represents the currently selected function in 3 bits. Which bit belongs to which function is described in arch/arm/mach-{codename}/{codename}_pinmux.c.