Re: [PATCH v9 3/4] dt-bindings: pps: pps-gpio PPS ECHO implementation

From: tom burkart
Date: Mon Dec 10 2018 - 21:17:43 EST

Quoting Rob Herring <robh@xxxxxxxxxx>:

On Mon, Nov 26, 2018 at 10:06 PM tom burkart <tom@xxxxxxxxxx> wrote:

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.

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?