On Thu, Jan 3, 2019 at 5:41 PM Thomas Petazzoni <thomas.petazzoni@xxxxxxxxxxx> wrote: > This commit extends the flags that can be used in GPIO specifiers to > indicate if a pull-up resistor or pull-down resistor should be > enabled. > > While some pinctrl DT bindings already offer the capability of > configuring pull-up/pull-down resistors at the pin level, a number of > simple GPIO controllers don't have any pinmuxing capability, and > therefore do not rely on the pinctrl DT bindings. > > Such simple GPIO controllers however sometimes allow to configure > pull-up and pull-down resistors on a per-pin basis, and whether such > resistors should be enabled or not is a highly board-specific HW > characteristic. > > By using two additional bits of the GPIO flag specifier, we can easily > allow the Device Tree to describe which GPIOs should have their > pull-up or pull-down resistors enabled. Even though the two options > are mutually exclusive, we still need two bits to encode at least > three states: no pull-up/pull-down, pull-up, pull-down. > > Signed-off-by: Thomas Petazzoni <thomas.petazzoni@xxxxxxxxxxx> > --- > Documentation/devicetree/bindings/gpio/gpio.txt | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt > index f0ba154b5723..03d8adf67c16 100644 > --- a/Documentation/devicetree/bindings/gpio/gpio.txt > +++ b/Documentation/devicetree/bindings/gpio/gpio.txt > @@ -67,6 +67,10 @@ Optional standard bitfield specifiers for the last cell: > https://en.wikipedia.org/wiki/Open_collector > - Bit 3: 0 means the output should be maintained during sleep/low-power mode > 1 means the output state can be lost during sleep/low-power mode > +- Bit 4: 0 means no pull-up resistor should be enabled > + 1 means a pull-up resistor should be enabled > +- Bit 5: 0 means no pull-down resistor should be enabled > + 1 means a pull-down resistor should be enabled As per the commit message this should be more verbose IMO, add something like "this setting will only apply to hardware with a simple on/off approach to pull up/down: if the hardware has more elaborate pull up/down settings such as specifying a specific resistance, the driver should use pin control bindings. Yours, Linus Walleij
