linux-kernel - Re: [PATCH] net/ethernet: update ret when ptp

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Date:   Fri, 06 Nov 2020 13:58:18 +0100
From:   Kurt Kanzenbach <kurt@...utronix.de>
To:     Arnd Bergmann <arnd@...nel.org>,
        Grygorii Strashko <grygorii.strashko@...com>
Cc:     Wang Qing <wangqing@...o.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Samuel Zou <zou_wei@...wei.com>,
        Richard Cochran <richardcochran@...il.com>,
        Networking <netdev@...r.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net/ethernet: update ret when ptp_clock is ERROR

On Fri Nov 06 2020, Arnd Bergmann wrote:
> On Fri, Nov 6, 2020 at 12:35 PM Grygorii Strashko
> <grygorii.strashko@...com> wrote:
>> On 06/11/2020 09:56, Wang Qing wrote:
>
>> > +++ b/drivers/net/ethernet/ti/am65-cpts.c
>> > @@ -1001,8 +1001,7 @@ struct am65_cpts *am65_cpts_create(struct device *dev, void __iomem *regs,
>>
>> there is
>>         cpts->ptp_clock = ptp_clock_register(&cpts->ptp_info, cpts->dev);
>>
>>
>> >       if (IS_ERR_OR_NULL(cpts->ptp_clock)) {
>>
>> And ptp_clock_register() can return NULL only if PTP support is disabled.
>> In which case, we should not even get here.
>>
>> So, I'd propose to s/IS_ERR_OR_NULL/IS_ERR above,
>> and just assign ret = PTR_ERR(cpts->ptp_clock) here.
>
> Right, using IS_ERR_OR_NULL() is almost ever a mistake, either
> from misunderstanding the interface, or from a badly designed
> interface that needs to be changed.

The NULL case should be handled differently and it is documented:

/**
 * ptp_clock_register() - register a PTP hardware clock driver
[...]
 * Returns a valid pointer on success or PTR_ERR on failure.  If PHC
 * support is missing at the configuration level, this function
 * returns NULL, and drivers are expected to gracefully handle that
 * case separately.
 */

Thanks,
Kurt

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