linux-kernel - Re: [PATCH 1/1] pps: clients: gpio: Bypass edge's direction check when not needed

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Date: Wed, 10 Apr 2024 16:46:15 +0200
From: Bastien Curutchet <bastien.curutchet@...tlin.com>
To: Rodolfo Giometti <giometti@...eenne.com>
Cc: linux-kernel@...r.kernel.org,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, herve.codina@...tlin.com,
 christophercordahi@...ometrics.ca
Subject: Re: [PATCH 1/1] pps: clients: gpio: Bypass edge's direction check
 when not needed

Hi Rodolfo,

On 4/10/24 16:23, Rodolfo Giometti wrote:
> On 10/04/24 13:35, Bastien Curutchet wrote:
>> In the IRQ handler, the GPIO's state is read to verify the direction of
>> the edge that triggered the interruption before generating the PPS event.
>> If a pulse is too short, the GPIO line can reach back its original state
>> before this verification and the PPS event is lost.
>>
>> This check is needed when info->capture_clear is set because it needs
>> interruptions on both rising and falling edges. When info->capture_clear
>> is not set, interruption is triggered by one edge only so this check can
>> be omitted.
>>
>> Bypass the edge's direction verification when info->capture_clear is not
>> set.
>>
>> Signed-off-by: Bastien Curutchet <bastien.curutchet@...tlin.com>
>> ---
>>   drivers/pps/clients/pps-gpio.c | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/drivers/pps/clients/pps-gpio.c 
>> b/drivers/pps/clients/pps-gpio.c
>> index 2f4b11b4dfcd..c2a96e3e3836 100644
>> --- a/drivers/pps/clients/pps-gpio.c
>> +++ b/drivers/pps/clients/pps-gpio.c
>> @@ -52,6 +52,15 @@ static irqreturn_t pps_gpio_irq_handler(int irq, 
>> void *data)
>>       info = data;
>> +    if (!info->capture_clear) {
>> +        /*
>> +         * If capture_clear is unset, IRQ is triggered by one edge only.
>> +         * So the check on edge direction is not needed here
>> +         */
>> +        pps_event(info->pps, &ts, PPS_CAPTUREASSERT, data);
>> +        return IRQ_HANDLED;
>> +    }
>> +
>>       rising_edge = gpiod_get_value(info->gpio_pin);
>>       if ((rising_edge && !info->assert_falling_edge) ||
>>               (!rising_edge && info->assert_falling_edge))
> 
> Apart the code duplication, which are the real benefits of doing so?
> 

It prevents from losing a PPS event when the pulse is so short (or the
kernel so busy) that the trailing edge of the pulse occurs before the
interrupt handler can read the state of the GPIO pin.


Best regards,
Bastien