linux-kernel - Re: [PATCH v4] pps: Add elapsed realtime timestamping

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Date:   Fri, 17 Mar 2023 17:34:28 +0100
From:   Rodolfo Giometti <giometti@...eenne.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Alex Komrakov <alexander.komrakov@...adcom.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] pps: Add elapsed realtime timestamping

On 17/03/23 15:22, Greg KH wrote:
> On Fri, Mar 17, 2023 at 03:04:31PM +0100, Rodolfo Giometti wrote:
>> On 17/03/23 10:51, Alex Komrakov wrote:
>>>> +     if (!(pps->info.mode & PPS_CAPTURECLEAR))
>>>> +             return 0;   Why are you not returning an error?
>>> [AK] I used the style in this file sysfs.c.
>>>    assert_show() and clear_show()  have the same condition.
>>> When '& PPS_CAPTURECLEAR' -- 0 means no interrupt asserted  and it is not error
>>> Probably Rodolfo can get more info why return 0
>>
>> It's just as Alex said, if the PPS source has no PPS_CAPTUREASSERT or
>> PPS_CAPTURECLEAR mode it should not print ASSERT and CLEAR info.
> 
> But shouldn't you return an error instead of an empty string?

This is not an error... it's just a disabled capability. :)

>>> And why are these sysfs files even present if the mode is not set
>>> properly?  Can the mode be set while the device is attached or is this
>>> only defined at probe time?  If at probe time, just never create these
>>> files.
>>> [AK] we can understand mode is set when interrupts asserted and
>>> file assert_elapsed will be updated.
>>
>> PPS source's "mode bits" can be set at runtime via PPS_SETPARAMS.
> 
> Ok, that's good to know.  But I think the error return value is a better
> indication that something went wrong here and this attribute does not
> work for this device at this point in time.

I see... however I suppose several code relays on this behavior.

If we decide to change it, which should be the better way to do it? Any 
suggestions are appreciated.

Ciao,

Rodolfo

-- 
GNU/Linux Solutions                  e-mail: giometti@...eenne.com
Linux Device Driver                          giometti@...ux.it
Embedded Systems                     phone:  +39 349 2432127
UNIX programming                     skype:  rodolfo.giometti