tegra124: Implement driver code for the pinmux, pingroup controls, and GPIOs.
The pins on tegra are controlled by three different units, the pinmux, the
pin group controls, and the GPIO banks. Each of these units controls some
aspect of the pins, and they layer together and interact in interesting ways.
By default, the GPIOs are configured to pass through the special purpose IO
that the pinmux is configured to and so can be ignored unless a GPIO is needed.
The pinmux controls which special purpose signal passes through, along with
pull ups, downs, and whether the output is tristated. The pingroup controls
change the parameters of a group of pins which all have to do with a related
The enum which holds constants related to the pinmux is relatively involved
and may not be entirely complete or correct due to slightly inconsistent,
incomplete, or missing docuemtnation related to the pinmux. Considerable
effort has been made to make it as accurate as possible. It includes a
constant which is the index into the pinmux control registers for that pin,
what each of the functions supported by that pin are, and which GPIO it
corresponds to. The GPIO constant is named after the GPIO and is the pinmux
register index for the pin for that GPIO. That way, when you need to turn on
a GPIO, you can use that constant along with the pinmux manipulating functions
to enable its tristate and pull up/down mode in addition to setting up the
Also, while in general I prefer not to use macros or the preprocessor when
writing C code, in this case the set of constants in the enums was too large
and cumbersome to manage without them. Since they're being used to construct
a table in a straightforward way, hopefully their negative aspects will be
In addition to the low level functions in each driver, the GPIO code also
includes some high level functions to set up input or output GPIOs since that
will probably be a very common thing to want to do.
TEST=Replaced the hardcoded pinmux configuration code for the UART pins and
saw that the UART still worked correctly. Added an infinite loop to the
bootblock that read and print the value of the lid switch over and over. Ran
it and toggled the lid switch on servo and saw that the output changed as
expected. Repeated that with the dev switch GPIO.
Signed-off-by: Gabe Black <email@example.com>
Reviewed-by: Ronald Minnich <firstname.lastname@example.org>
Reviewed-by: David Hendricks <email@example.com>
Commit-Queue: Gabe Black <firstname.lastname@example.org>
Tested-by: Gabe Black <email@example.com>
10 files changed