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

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Message-ID: <4752oq01-879s-0p0p-s8qq-sn48q27sp1r7@syhkavp.arg>
Date:   Mon, 20 Mar 2023 09:43:30 -0400 (EDT)
From:   Nicolas Pitre <nico@...xnic.net>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
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 Mon, 20 Mar 2023, Andy Shevchenko wrote:

> 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?

To my knowledge it is not.

The current arrangement has apparently worked well for more than 6 
years. If you see a better way you're welcome to submit patches as 
usual.

Alternatively the above commit can be reverted if no one else 
cares. I personally gave up on the idea of a slimmed down Linux kernel a 
while ago.


Nicolas