netdev - Re: [PATCH v1] ptp: add ToD device driver for Intel FPGA cards

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Message-ID: <ZBhdnl1OAPcrLdHD@smile.fi.intel.com>
Date:   Mon, 20 Mar 2023 15:20:30 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Nicolas Pitre <nico@...xnic.net>
Cc:     Richard Cochran <richardcochran@...il.com>,
        Tianfei Zhang <tianfei.zhang@...el.com>,
        netdev@...r.kernel.org, linux-fpga@...r.kernel.org,
        ilpo.jarvinen@...ux.intel.com, russell.h.weight@...el.com,
        matthew.gerlach@...ux.intel.com,
        pierre-louis.bossart@...ux.intel.com, vinicius.gomes@...el.com,
        Raghavendra Khadatare <raghavendrax.anand.khadatare@...el.com>
Subject: Re: [PATCH v1] ptp: add ToD device driver for Intel FPGA cards

On Wed, Mar 15, 2023 at 10:37:58AM -0400, Nicolas Pitre wrote:
> On Wed, 15 Mar 2023, Andy Shevchenko wrote:
> > On Tue, Mar 14, 2023 at 12:46:48PM -0700, Richard Cochran wrote:
> > > On Tue, Mar 14, 2023 at 12:47:03PM +0200, Andy Shevchenko wrote:
> > > > The semantics of the above is similar to gpiod_get_optional() and since NULL
> > > > is a valid return in such cases, the PTP has to handle this transparently to
> > > > the user. Otherwise it's badly designed API which has to be fixed.
> > > 
> > > Does it now?  Whatever.
> > > 
> > > > TL;DR: If I'm mistaken, I would like to know why.
> > > 
> > > git log.  git blame.
> > > 
> > > Get to know the tools of trade.
> > 
> > So, the culprit seems the commit d1cbfd771ce8 ("ptp_clock: Allow for it
> > to be optional") which did it half way.
> > 
> > Now I would like to know why the good idea got bad implementation.
> > 
> > Nicolas?
> 
> I'd be happy to help but as presented I simply don't know what you're 
> talking about. Please give me more context.

When your change introduced the optionality of the above mentioned API,
i.e. ptp_clock_register(), the function started returning NULL, which
is fine. What's not in my opinion is to ask individual drivers to handle it.
That said, if we take a look at gpiod_*_optional() or clk_*_optional()
we may notice that they handle NULL as a valid parameter (object) to their
respective APIs and individual drivers shouldn't take care about that.

Why PTP is so special?

-- 
With Best Regards,
Andy Shevchenko