linux-kernel - Re: [RESEND PATCH v2 3/3] rtc: Add driver for Nuvoton ma35d1 rtc controller

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Date:   Wed, 9 Aug 2023 04:12:24 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Jacky Huang <ychuang570808@...il.com>
Cc:     a.zummo@...ertech.it, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        linux-rtc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        soc@...nel.org, mjchen@...oton.com, schung@...oton.com,
        Jacky Huang <ychuang3@...oton.com>
Subject: Re: [RESEND PATCH v2 3/3] rtc: Add driver for Nuvoton ma35d1 rtc
 controller

On 09/08/2023 04:10:27+0200, Alexandre Belloni wrote:
> > +static int ma35d1_rtc_probe(struct platform_device *pdev)
> > +{
> > +	struct ma35_rtc *rtc;
> > +	struct clk *clk;
> > +	u32 regval;
> > +	int err;
> > +
> > +	rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL);
> > +	if (!rtc)
> > +		return -ENOMEM;
> > +
> > +	rtc->rtc_reg = devm_platform_ioremap_resource(pdev, 0);
> > +	if (IS_ERR(rtc->rtc_reg))
> > +		return PTR_ERR(rtc->rtc_reg);
> > +
> > +	clk = of_clk_get(pdev->dev.of_node, 0);
> > +	if (IS_ERR(clk))
> > +		return dev_err_probe(&pdev->dev, PTR_ERR(clk), "failed to find rtc clock\n");
> > +
> > +	err = clk_prepare_enable(clk);
> > +	if (err)
> > +		return -ENOENT;
> > +
> > +	platform_set_drvdata(pdev, rtc);
> > +
> > +	rtc->rtcdev = devm_rtc_device_register(&pdev->dev, pdev->name,
> > +					       &ma35d1_rtc_ops, THIS_MODULE);
> > +	if (IS_ERR(rtc->rtcdev))
> > +		return dev_err_probe(&pdev->dev, PTR_ERR(rtc->rtcdev),
> > +				     "failed to register rtc device\n");
> 
> This MUST be done last in probe, else you open a race with userspace.
> 
> 
> > +
> > +	err = ma35d1_rtc_init(rtc, RTC_INIT_TIMEOUT);
> > +	if (err)
> > +		return err;
> > +
> 
> I don't believe you should do this on every probe but only when this
> hasn't been done yet.
> 

Also, if you can know that the time has never been set, don't discard
this information, this is crucial information and it needs to be
reported to userspace.


-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com