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

From: Alexandre Belloni <alexandre.belloni@bootlin.com>
To: Jacky Huang <ychuang570808@gmail.com>
Cc: a.zummo@towertech.it, robh+dt@kernel.org,
	krzysztof.kozlowski+dt@linaro.org, conor+dt@kernel.org,
	linux-rtc@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, soc@kernel.org,
	mjchen@nuvoton.com, schung@nuvoton.com,
	Jacky Huang <ychuang3@nuvoton.com>
Subject: Re: [RESEND PATCH v2 3/3] rtc: Add driver for Nuvoton ma35d1 rtc controller
Date: Wed, 9 Aug 2023 04:12:24 +0200	[thread overview]
Message-ID: <20230809021224ab4f229f@mail.local> (raw)
In-Reply-To: <20230809021025a7c0daec@mail.local>

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