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

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Date:   Fri, 17 Mar 2023 15:22:47 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Rodolfo Giometti <giometti@...eenne.com>
Cc:     Alex Komrakov <alexander.komrakov@...adcom.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] pps: Add elapsed realtime timestamping

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?

> > 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.

thanks,

greg k-h