netdev - RE: [PATCH v2] ptp: add ToD device driver for Intel FPGA cards

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Date:   Wed, 22 Mar 2023 15:36:25 +0000
From:   "Zhang, Tianfei" <tianfei.zhang@...el.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
CC:     "richardcochran@...il.com" <richardcochran@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-fpga@...r.kernel.org" <linux-fpga@...r.kernel.org>,
        "ilpo.jarvinen@...ux.intel.com" <ilpo.jarvinen@...ux.intel.com>,
        "Gomes, Vinicius" <vinicius.gomes@...el.com>,
        "pierre-louis.bossart@...ux.intel.com" 
        <pierre-louis.bossart@...ux.intel.com>,
        Marco Pagani <marpagan@...hat.com>,
        "Weight, Russell H" <russell.h.weight@...el.com>,
        "matthew.gerlach@...ux.intel.com" <matthew.gerlach@...ux.intel.com>,
        "nico@...xnic.net" <nico@...xnic.net>,
        "Khadatare, RaghavendraX Anand" 
        <raghavendrax.anand.khadatare@...el.com>
Subject: RE: [PATCH v2] ptp: add ToD device driver for Intel FPGA cards



> -----Original Message-----
> From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Sent: Wednesday, March 22, 2023 11:04 PM
> To: Zhang, Tianfei <tianfei.zhang@...el.com>
> Cc: richardcochran@...il.com; netdev@...r.kernel.org; linux-
> fpga@...r.kernel.org; ilpo.jarvinen@...ux.intel.com; Gomes, Vinicius
> <vinicius.gomes@...el.com>; pierre-louis.bossart@...ux.intel.com; Pagani, Marco
> <marpagan@...hat.com>; Weight, Russell H <russell.h.weight@...el.com>;
> matthew.gerlach@...ux.intel.com; nico@...xnic.net; Khadatare, RaghavendraX
> Anand <raghavendrax.anand.khadatare@...el.com>
> Subject: Re: [PATCH v2] ptp: add ToD device driver for Intel FPGA cards
> 
> On Wed, Mar 22, 2023 at 02:59:21PM +0000, Zhang, Tianfei wrote:
> > > -----Original Message-----
> > > From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > > Sent: Wednesday, March 22, 2023 10:49 PM
> > > To: Zhang, Tianfei <tianfei.zhang@...el.com>
> > > Cc: richardcochran@...il.com; netdev@...r.kernel.org; linux-
> > > fpga@...r.kernel.org; ilpo.jarvinen@...ux.intel.com; Gomes, Vinicius
> > > <vinicius.gomes@...el.com>; pierre-louis.bossart@...ux.intel.com;
> > > Pagani, Marco <marpagan@...hat.com>; Weight, Russell H
> > > <russell.h.weight@...el.com>; matthew.gerlach@...ux.intel.com;
> > > nico@...xnic.net; Khadatare, RaghavendraX Anand
> > > <raghavendrax.anand.khadatare@...el.com>
> > > Subject: Re: [PATCH v2] ptp: add ToD device driver for Intel FPGA
> > > cards
> > >
> > > On Wed, Mar 22, 2023 at 10:35:47AM -0400, Tianfei Zhang wrote:
> > > > Adding a DFL (Device Feature List) device driver of ToD device for
> > > > Intel FPGA cards.
> > > >
> > > > The Intel FPGA Time of Day(ToD) IP within the FPGA DFL bus is
> > > > exposed as PTP Hardware clock(PHC) device to the Linux PTP stack
> > > > to synchronize the system clock to its ToD information using
> > > > phc2sys utility of the Linux PTP stack. The DFL is a hardware List
> > > > within FPGA, which defines a linked list of feature headers within
> > > > the device MMIO space to provide an extensible way of adding subdevice
> features.
> 
> ...
> 
> > > > +	dt->ptp_clock = ptp_clock_register(&dt->ptp_clock_ops, dev);
> > > > +	if (IS_ERR_OR_NULL(dt->ptp_clock))
> > > > +		return dev_err_probe(dt->dev, PTR_ERR_OR_ZERO(dt->ptp_clock),
> > > > +				     "Unable to register PTP clock\n");
> > > > +
> > > > +	return 0;
> > >
> > > Can be as simple as:
> > >
> > > 	ret = PTR_ERR_OR_ZERO(dt->ptp_clock);
> > > 	return dev_err_probe(dt->dev, ret, "Unable to register PTP
> > > clock\n");
> >
> >             This should be :
> >            ret = PTR_ERR_OR_ZERO(dt->ptp_clock);
> >            if (ret)
> >                     return dev_err_probe(dt->dev, ret, "Unable to register PTP clock\n");
> >            return 0;
> 
> It depends how you treat the NULL from ptp_clock_register() and why driver will be
> still bound to the device even if it doesn't provide PTP facility.

For this ToD DFL driver, it depends on CONFIG_PTP_1588_CLOCK, I will add this dependency in Kconfig file later as Ilpo pointed out.
It will not occurred the NULL case for ptp_clock_register() in this driver, so it only handle the error case is enough.