Messages in this thread | | | Date | Wed, 12 Dec 2018 13:25:51 +1100 | From | tom burkart <> | Subject | Re: [PATCH v9 3/4] dt-bindings: pps: pps-gpio PPS ECHO implementation |
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Quoting Rob Herring <robh@kernel.org>:
> On Mon, Dec 10, 2018 at 8:17 PM tom burkart <tom@aussec.com> wrote: >> >> Quoting Rob Herring <robh@kernel.org>: >> >> > On Mon, Nov 26, 2018 at 10:06 PM tom burkart <tom@aussec.com> wrote: >> >> >> >> Quoting Rob Herring <robh@kernel.org>: >> >> >> >> > On Thu, Nov 22, 2018 at 3:49 AM Tom Burkart <tom@aussec.com> 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@fridolin.com> >> >> >> Signed-off-by: Tom Burkart <tom@aussec.com> >> >> >> --- >> >> >> 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. >> >> Hi Rob, >> I have looked at the appropriate changes to my code to implement the >> above. However, there is no GPIO_ACTIVE_* as part of the gpiod_flags >> enum (include/linux/gpio/consumer.h). >> >> What am I missing? > > You don't need to know in the driver. You set the gpio state to 1 for > active, 0 for inactive and that does the right thing based on the flag > in the DT. IOW, if the DT defines the GPIO as active low, then setting > the gpio state to 1 will result in the GPIO being 0V. It's a bit > annoying and confusing at first until you realize the driver can just > handle either polarity transparently.
Hi Rob, thanks a lot! The penny finally dropped.
My patch v12 will have the changes implemented (no invert-pps-echo).
Tom
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