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

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Date: Thu, 25 Apr 2024 13:46:40 +0200
From: Rodolfo Giometti <giometti@...eenne.com>
To: Bastien Curutchet <bastien.curutchet@...tlin.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

On 25/04/24 08:11, Bastien Curutchet wrote:
> Hi Rodolfo,
> 
> 
> On 4/12/24 14:20, Bastien Curutchet wrote:
>> Hi Rodolfo,
>>
>> On 4/12/24 08:44, Rodolfo Giometti wrote:
>>> On 11/04/24 14:44, Bastien Curutchet wrote:
>>>>>
>>>>> However we should think very well about this modification since it could be 
>>>>> the case where we have a device sending both assert and clear events but we 
>>>>> wish to catch just the asserts... in this case we will get doubled asserts!
>>>>>
>>>>
>>>> My understanding is that clear events are to be captured only when this
>>>> capture_clear boolean is set. If it is not set, the PPS_CAPTURECLEAR
>>>> flag is not added to pps_source_info->mode and get_irqf_trigger_flags()
>>>> will return only one edge flag (rising or falling depending on
>>>> assert-falling-edge DT property).
>>>
>>> Yes. You are right.
>>>
>>>> By the way, I see that the capture_clear is never set since the legacy
>>>> platform data support has been dropped (commit ee89646619ba).
>>>
>>> I see, but it can be re-enabled in the future... In this scenario, I think we 
>>> should add a DT entry to enable this special behavior. Maybe we can also add 
>>> a warning as below: >
>>> static irqreturn_t pps_gpio_irq_handler(int irq, void *data)
>>> {
>>>          ...
>>>          if ((rising_edge && !info->assert_falling_edge) ||
>>>                          (!rising_edge && info->assert_falling_edge))
>>>                  pps_event(info->pps, &ts, PPS_CAPTUREASSERT, data);
>>>          else if (info->capture_clear &&
>>>                          ((rising_edge && info->assert_falling_edge) ||
>>>                          (!rising_edge && !info->assert_falling_edge)))
>>>                  pps_event(info->pps, &ts, PPS_CAPTURECLEAR, data);
>>>      else
>>>          dev_warn_ratelimited(dev, "no ASSERT or CAPTURE event? "
>>>              "Maybe you need support-tiny-assert-pulse?");
>>>
>>>          return IRQ_HANDLED;
>>> }
>>>
>>
>> I'm not sure a DT entry is needed. IMO there are two cases:
>>   1) capture_clear is unset. We need to capture only assert events,
>>      interrupt will be triggered by assert edge only so there is no need
>>      to check GPIO state: we can use the bypass.
>>   2) capture_clear is set. We need to capture assert and/or clear
>>      events, interrupt will be triggered by both assert and clear edges
>>      so we can't avoid the GPIO state checking to distinguish clear
>>      events from assert events: we can't use the bypass.
>>
>> So if we bypass the GPIO's state check when capture_clear is unset and
>> leave current behavior when capture_clear is set:
>>   - case 1) will be more efficient and we won't lose tiny pulses anymore
>>   - case 2) is unchanged: we still might lose tiny pulses but as bypass
>> can't be done here, I think that we can't do better.
>>
>> I agree that adding warning when the handler is left without triggering
>> a pps event can be useful, I can add it in a V3 version.
>>
> 
> Would this be OK for you ? If yes, I'll send a V3 version without DT
> entry but with an additional warning.

Sorry, I completely missed this e-mail! :(

OK, I agree.

Ciao,

Rodolfo

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