From: Andrew Lunn [mailto:andrew@lunn.ch]
Sent: Thursday, September 28, 2017 12:36 PM

I assume ptp already has the core code to use pinctrl and Linux
standard GPIOs? What does the device tree binding look like? How do
you specify the GPIOs to use?

What we want to avoid is defining an ABI now, otherwise it is going to
be hard to swap to pinctrl later.

A ptp_clock_info has an array of struct ptp_pin_desc which defines "pins" with a name ("Hardware specific human readable pin name"), an index, and a bitmask of valid functions. The ptp_pin_desc structure is shared with usermode for the PTP_PIN_GETFUNC and PTP_PIN_SETFUNC ioctls. The pins are also exposed in sysfs (see Documentation/ABI/testing/sysfs-ptp). The underlying implementation for configuring the hardware is left up to the PHC driver. I don't see any drivers today that use the PHC pin API as a layer over pinctrl/gpiochip, but there's no reason that that couldn't be the case.

For mv88e6xxx, we name the pins using the pattern "mv88e6xxx_gpio%d"; this appears to be in line with current practice (igb_ptp.c uses "SDP%d", mlx5 driver uses "mlx5_pps%d"). Usermode code appears to be expected to determine which pin it needs to use. (Our current userspace code, for instance, knows that it needs to find "mv88e6xxx_gpio8".)

For mv88e6xxx, Device Tree does feel like a better option here for declaring names, functions, and pin usages. Not all platforms that use the PTP API use Device Tree though.

-- brandon