On Mon, Nov 26, 2018 at 10:06 PM tom burkart <tom@xxxxxxxxxx> wrote: > > Hi Rob, > > Quoting Rob Herring <robh@xxxxxxxxxx>: > > > On Thu, Nov 22, 2018 at 3:49 AM Tom Burkart <tom@xxxxxxxxxx> wrote: > >> > >> This patch implements the device tree changes required for the pps > >> echo functionality for pps-gpio, that sysfs claims is available > >> already. > >> > >> This patch was originally written by Lukas Senger as part of a masters > >> thesis project and modified for inclusion into the linux kernel by Tom > >> Burkart. > >> > >> Signed-off-by: Lukas Senger <lukas@xxxxxxxxxxxx> > >> Signed-off-by: Tom Burkart <tom@xxxxxxxxxx> > >> --- > >> Documentation/devicetree/bindings/pps/pps-gpio.txt | 9 +++++++++ > >> 1 file changed, 9 insertions(+) > >> > >> diff --git a/Documentation/devicetree/bindings/pps/pps-gpio.txt > >> b/Documentation/devicetree/bindings/pps/pps-gpio.txt > >> index 1155d49c2699..e09f6f2405c5 100644 > >> --- a/Documentation/devicetree/bindings/pps/pps-gpio.txt > >> +++ b/Documentation/devicetree/bindings/pps/pps-gpio.txt > >> @@ -7,10 +7,15 @@ Required properties: > >> - compatible: should be "pps-gpio" > >> - gpios: one PPS GPIO in the format described by ../gpio/gpio.txt > >> > >> +Additional required properties for the PPS ECHO functionality: > >> +- echo-gpios: one PPS ECHO GPIO in the format described by ../gpio/gpio.txt > >> +- echo-active-ms: duration in ms of the active portion of the echo pulse > >> + > >> Optional properties: > >> - assert-falling-edge: when present, assert is indicated by a falling edge > >> (instead of by a rising edge) > >> - capture-clear: when present, also capture the PPS clear event > >> +- invert-pps-echo: when present, invert the PPS ECHO pulse > > > > Why do you need this? Can't you just make the echo gpio GPIO_ACTIVE_LOW? > > > > BTW, using the flag probably should have been done for > > 'assert-falling-edge' as well. > > The hardware I use expects a positive-going echo pulse, however, it > was really easy to give users the option to have it inverted in case > they use different hardware that expects a negative-going edge. It will be even easier to implement if you use GPIO_ACTIVE_LOW or GPIO_ACTIVE_HIGH as appropriate. If the flag is set appropriately, then gpiod_set_value(gpio, 1) asserts the pulse and gpiod_set_value(gpio, 0) deasserts it no matter which way the h/w is wired. You can then get rid of invert_pps_echo in the driver. Rob
