Date:   Fri, 2 Dec 2016 10:56:46 -0700
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Amelie Delaunay <amelie.delaunay@...com>
Cc:     a.zummo@...ertech.it, alexandre.belloni@...e-electrons.com,
        robh+dt@...nel.org, mark.rutland@....com,
        mcoquelin.stm32@...il.com, alexandre.torgue@...com,
        linux@...linux.org.uk, rtc-linux@...glegroups.com,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, gabriel.fernandez@...com
Subject: Re: [PATCH 3/8] rtc: add STM32 RTC driver

On Fri, Dec 02, 2016 at 03:09:56PM +0100, Amelie Delaunay wrote:
> This patch adds support for the STM32 RTC.

Hello Amelie,

> 
> Signed-off-by: Amelie Delaunay <amelie.delaunay@...com>
> ---
>  drivers/rtc/Kconfig     |  10 +
>  drivers/rtc/Makefile    |   1 +
>  drivers/rtc/rtc-stm32.c | 777 ++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 788 insertions(+)
>  create mode 100644 drivers/rtc/rtc-stm32.c
> 
> diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
> index e859d14..dd8b218 100644
> --- a/drivers/rtc/Kconfig
> +++ b/drivers/rtc/Kconfig
> @@ -1706,6 +1706,16 @@ config RTC_DRV_PIC32
>  	   This driver can also be built as a module. If so, the module
>  	   will be called rtc-pic32
>  
> +config RTC_DRV_STM32
> +	tristate "STM32 On-Chip RTC"
> +	depends on ARCH_STM32
> +	help
> +	   If you say yes here you get support for the STM32 On-Chip
> +	   Real Time Clock.
> +
> +	   This driver can also be built as a module, if so, the module
> +	   will be called "rtc-stm32".
> +
>  comment "HID Sensor RTC drivers"
>  
>  config RTC_DRV_HID_SENSOR_TIME
> diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
> index 1ac694a..87bd9cc 100644
> --- a/drivers/rtc/Makefile
> +++ b/drivers/rtc/Makefile
> @@ -144,6 +144,7 @@ obj-$(CONFIG_RTC_DRV_SNVS)	+= rtc-snvs.o
>  obj-$(CONFIG_RTC_DRV_SPEAR)	+= rtc-spear.o
>  obj-$(CONFIG_RTC_DRV_STARFIRE)	+= rtc-starfire.o
>  obj-$(CONFIG_RTC_DRV_STK17TA8)	+= rtc-stk17ta8.o
> +obj-$(CONFIG_RTC_DRV_STM32) 	+= rtc-stm32.o
>  obj-$(CONFIG_RTC_DRV_STMP)	+= rtc-stmp3xxx.o
>  obj-$(CONFIG_RTC_DRV_ST_LPC)	+= rtc-st-lpc.o
>  obj-$(CONFIG_RTC_DRV_SUN4V)	+= rtc-sun4v.o
> diff --git a/drivers/rtc/rtc-stm32.c b/drivers/rtc/rtc-stm32.c
> new file mode 100644
> index 0000000..9e710ff
> --- /dev/null
> +++ b/drivers/rtc/rtc-stm32.c
> @@ -0,0 +1,777 @@
> +/*
> + * Copyright (C) Amelie Delaunay 2015
> + * Author:  Amelie Delaunay <adelaunay.stm32@...il.com>
> + * License terms:  GNU General Public License (GPL), version 2
> + */
> +
> +#include <linux/bcd.h>
> +#include <linux/clk.h>
> +#include <linux/init.h>
> +#include <linux/io.h>
> +#include <linux/iopoll.h>
> +#include <linux/ioport.h>
> +#include <linux/kernel.h>
> +#include <linux/mfd/syscon.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/platform_device.h>
> +#include <linux/regmap.h>
> +#include <linux/rtc.h>
> +#include <linux/spinlock.h>
> +
> +#define DRIVER_NAME "stm32_rtc"
> +
> +/* STM32 RTC registers */
> +#define STM32_RTC_TR		0x00
> +#define STM32_RTC_DR		0x04
> +#define STM32_RTC_CR		0x08
> +#define STM32_RTC_ISR		0x0C
> +#define STM32_RTC_PRER		0x10
> +#define STM32_RTC_ALRMAR	0x1C
> +#define STM32_RTC_WPR		0x24
> +
> +/* STM32_RTC_TR bit fields  */
> +#define STM32_RTC_TR_SEC_SHIFT		0
> +#define STM32_RTC_TR_SEC		GENMASK(6, 0)
> +#define STM32_RTC_TR_MIN_SHIFT		8
> +#define STM32_RTC_TR_MIN		GENMASK(14, 8)
> +#define STM32_RTC_TR_HOUR_SHIFT		16
> +#define STM32_RTC_TR_HOUR		GENMASK(21, 16)
> +
> +/* STM32_RTC_DR bit fields */
> +#define STM32_RTC_DR_DATE_SHIFT		0
> +#define STM32_RTC_DR_DATE		GENMASK(5, 0)
> +#define STM32_RTC_DR_MONTH_SHIFT	8
> +#define STM32_RTC_DR_MONTH		GENMASK(11, 8)
> +#define STM32_RTC_DR_WDAY_SHIFT		13
> +#define STM32_RTC_DR_WDAY		GENMASK(15, 13)
> +#define STM32_RTC_DR_YEAR_SHIFT		16
> +#define STM32_RTC_DR_YEAR		GENMASK(23, 16)
> +
> +/* STM32_RTC_CR bit fields */
> +#define STM32_RTC_CR_FMT		BIT(6)
> +#define STM32_RTC_CR_ALRAE		BIT(8)
> +#define STM32_RTC_CR_ALRAIE		BIT(12)
> +
> +/* STM32_RTC_ISR bit fields */
> +#define STM32_RTC_ISR_ALRAWF		BIT(0)
> +#define STM32_RTC_ISR_INITS		BIT(4)
> +#define STM32_RTC_ISR_RSF		BIT(5)
> +#define STM32_RTC_ISR_INITF		BIT(6)
> +#define STM32_RTC_ISR_INIT		BIT(7)
> +#define STM32_RTC_ISR_ALRAF		BIT(8)
> +
> +/* STM32_RTC_PRER bit fields */
> +#define STM32_RTC_PRER_PRED_S_SHIFT	0
> +#define STM32_RTC_PRER_PRED_S		GENMASK(14, 0)
> +#define STM32_RTC_PRER_PRED_A_SHIFT	16
> +#define STM32_RTC_PRER_PRED_A		GENMASK(22, 16)
> +
> +/* STM32_RTC_ALRMAR and STM32_RTC_ALRMBR bit fields */
> +#define STM32_RTC_ALRMXR_SEC_SHIFT	0
> +#define STM32_RTC_ALRMXR_SEC		GENMASK(6, 0)
> +#define STM32_RTC_ALRMXR_SEC_MASK	BIT(7)
> +#define STM32_RTC_ALRMXR_MIN_SHIFT	8
> +#define STM32_RTC_ALRMXR_MIN		GENMASK(14, 8)
> +#define STM32_RTC_ALRMXR_MIN_MASK	BIT(15)
> +#define STM32_RTC_ALRMXR_HOUR_SHIFT	16
> +#define STM32_RTC_ALRMXR_HOUR		GENMASK(21, 16)
> +#define STM32_RTC_ALRMXR_PM		BIT(22)
> +#define STM32_RTC_ALRMXR_HOUR_MASK	BIT(23)
> +#define STM32_RTC_ALRMXR_DATE_SHIFT	24
> +#define STM32_RTC_ALRMXR_DATE		GENMASK(29, 24)
> +#define STM32_RTC_ALRMXR_WDSEL		BIT(30)
> +#define STM32_RTC_ALRMXR_WDAY_SHIFT	24
> +#define STM32_RTC_ALRMXR_WDAY		GENMASK(27, 24)
> +#define STM32_RTC_ALRMXR_DATE_MASK	BIT(31)
> +
> +/* STM32_RTC_WPR key constants */
> +#define RTC_WPR_1ST_KEY			0xCA
> +#define RTC_WPR_2ND_KEY			0x53
> +#define RTC_WPR_WRONG_KEY		0xFF
> +
> +/*
> + * RTC registers are protected agains parasitic write access.
> + * PWR_CR_DBP bit must be set to enable write access to RTC registers.
> + */
> +/* STM32_PWR_CR */
> +#define PWR_CR				0x00
> +/* STM32_PWR_CR bit field */
> +#define PWR_CR_DBP			BIT(8)
> +
> +static struct regmap *dbp;
> +
> +struct stm32_rtc {
> +	struct rtc_device *rtc_dev;
> +	void __iomem *base;
> +	struct clk *pclk;
> +	struct clk *ck_rtc;
> +	unsigned int clksrc;
> +	spinlock_t lock; /* Protects registers accesses */
> +	int irq_alarm;
> +	struct regmap *pwrcr;
> +};
> +
> +static inline unsigned int stm32_rtc_readl(struct stm32_rtc *rtc,
> +					   unsigned int offset)
> +{
> +	return readl_relaxed(rtc->base + offset);
> +}
> +
> +static inline void stm32_rtc_writel(struct stm32_rtc *rtc,
> +				    unsigned int offset, unsigned int value)
> +{
> +	writel_relaxed(value, rtc->base + offset);
> +}

I'm not sure wrapping the readl/writel_relaxed function does anything special
other than simply redirecting the reader to another section of the code.

> +
> +static void stm32_rtc_wpr_unlock(struct stm32_rtc *rtc)
> +{
> +//	if (dbp)
> +//		regmap_update_bits(dbp, PWR_CR, PWR_CR_DBP, PWR_CR_DBP);

Did checkpatch let you get away with this?  What did you intend to do here? 

> +
> +	stm32_rtc_writel(rtc, STM32_RTC_WPR, RTC_WPR_1ST_KEY);
> +	stm32_rtc_writel(rtc, STM32_RTC_WPR, RTC_WPR_2ND_KEY);
> +}
> +
> +static void stm32_rtc_wpr_lock(struct stm32_rtc *rtc)
> +{
> +	stm32_rtc_writel(rtc, STM32_RTC_WPR, RTC_WPR_WRONG_KEY);
> +
> +//	if (dbp)
> +//		regmap_update_bits(dbp, PWR_CR, PWR_CR_DBP, ~PWR_CR_DBP);
> +}
> +
> +static int stm32_rtc_enter_init_mode(struct stm32_rtc *rtc)
> +{
> +	unsigned int isr = stm32_rtc_readl(rtc, STM32_RTC_ISR);
> +
> +	if (!(isr & STM32_RTC_ISR_INITF)) {
> +		isr |= STM32_RTC_ISR_INIT;
> +		stm32_rtc_writel(rtc, STM32_RTC_ISR, isr);
> +
> +		return readl_relaxed_poll_timeout_atomic(
> +					rtc->base + STM32_RTC_ISR,
> +					isr, (isr & STM32_RTC_ISR_INITF),
> +					10, 100000);

When using hard coded numerics please add comments that explains the reason
behind the selected values.

> +	}
> +
> +	return 0;
> +}
> +
> +static void stm32_rtc_exit_init_mode(struct stm32_rtc *rtc)
> +{
> +	unsigned int isr = stm32_rtc_readl(rtc, STM32_RTC_ISR);
> +
> +	isr &= ~STM32_RTC_ISR_INIT;
> +	stm32_rtc_writel(rtc, STM32_RTC_ISR, isr);
> +}
> +
> +static int stm32_rtc_wait_sync(struct stm32_rtc *rtc)
> +{
> +	unsigned int isr;
> +
> +	isr = stm32_rtc_readl(rtc, STM32_RTC_ISR);
> +
> +	isr &= ~STM32_RTC_ISR_RSF;
> +	stm32_rtc_writel(rtc, STM32_RTC_ISR, isr);
> +
> +	/* Wait the registers to be synchronised */
> +	return readl_relaxed_poll_timeout_atomic(rtc->base + STM32_RTC_ISR,
> +						 isr,
> +						 (isr & STM32_RTC_ISR_RSF),
> +						 10, 100000);

Shouldn't the break condition be !((isr & STM32_RTC_ISR_RSF) ?  If not this
probably deserve a better comment.

> +}
> +
> +static irqreturn_t stm32_rtc_alarm_irq(int irq, void *dev_id)
> +{
> +	struct stm32_rtc *rtc = (struct stm32_rtc *)dev_id;
> +	unsigned long irqflags, events = 0;
> +	unsigned int isr, cr;
> +
> +	spin_lock_irqsave(&rtc->lock, irqflags);
> +
> +	isr = stm32_rtc_readl(rtc, STM32_RTC_ISR);
> +	cr = stm32_rtc_readl(rtc, STM32_RTC_CR);
> +
> +	if ((isr & STM32_RTC_ISR_ALRAF) &&
> +	    (cr & STM32_RTC_CR_ALRAIE)) {
> +		/* Alarm A flag - Alarm interrupt */
> +		events |= RTC_IRQF | RTC_AF;
> +		isr &= ~STM32_RTC_ISR_ALRAF;
> +	}
> +
> +	/* Clear event irqflags, otherwise new events won't be received */
> +	stm32_rtc_writel(rtc, STM32_RTC_ISR, isr);
> +
> +	spin_unlock_irqrestore(&rtc->lock, irqflags);
> +
> +	if (events) {
> +		dev_info(&rtc->rtc_dev->dev, "Alarm occurred\n");
> +
> +		/* Pass event to the kernel */
> +		rtc_update_irq(rtc->rtc_dev, 1, events);
> +		return IRQ_HANDLED;
> +	} else {
> +		return IRQ_NONE;
> +	}
> +}
> +
> +/* Convert rtc_time structure from bin to bcd format */
> +static void tm2bcd(struct rtc_time *tm)
> +{
> +	tm->tm_sec = bin2bcd(tm->tm_sec);
> +	tm->tm_min = bin2bcd(tm->tm_min);
> +	tm->tm_hour = bin2bcd(tm->tm_hour);
> +
> +	tm->tm_mday = bin2bcd(tm->tm_mday);
> +	tm->tm_mon = bin2bcd(tm->tm_mon + 1);
> +	tm->tm_year = bin2bcd(tm->tm_year - 100);
> +	/*
> +	 * Number of days since Sunday
> +	 * - on kernel side, 0=Sunday...6=Saturday
> +	 * - on rtc side, 0=invalid,1=Monday...7=Sunday
> +	 */
> +	tm->tm_wday = (!tm->tm_wday) ? 7 : tm->tm_wday;
> +}
> +
> +/* Convert rtc_time structure from bcd to bin format */
> +static void bcd2tm(struct rtc_time *tm)
> +{
> +	tm->tm_sec = bcd2bin(tm->tm_sec);
> +	tm->tm_min = bcd2bin(tm->tm_min);
> +	tm->tm_hour = bcd2bin(tm->tm_hour);
> +
> +	tm->tm_mday = bcd2bin(tm->tm_mday);
> +	tm->tm_mon = bcd2bin(tm->tm_mon) - 1;
> +	tm->tm_year = bcd2bin(tm->tm_year) + 100;
> +	/*
> +	 * Number of days since Sunday
> +	 * - on kernel side, 0=Sunday...6=Saturday
> +	 * - on rtc side, 0=invalid,1=Monday...7=Sunday
> +	 */
> +	tm->tm_wday %= 7;
> +}
> +
> +static int stm32_rtc_read_time(struct device *dev, struct rtc_time *tm)
> +{
> +	struct stm32_rtc *rtc = dev_get_drvdata(dev);
> +	unsigned int tr, dr;
> +	unsigned long irqflags;
> +
> +	spin_lock_irqsave(&rtc->lock, irqflags);
> +
> +	/* Time and Date in BCD format */
> +	tr = stm32_rtc_readl(rtc, STM32_RTC_TR);
> +	dr = stm32_rtc_readl(rtc, STM32_RTC_DR);
> +
> +	spin_unlock_irqrestore(&rtc->lock, irqflags);
> +
> +	tm->tm_sec = (tr & STM32_RTC_TR_SEC) >> STM32_RTC_TR_SEC_SHIFT;
> +	tm->tm_min = (tr & STM32_RTC_TR_MIN) >> STM32_RTC_TR_MIN_SHIFT;
> +	tm->tm_hour = (tr & STM32_RTC_TR_HOUR) >> STM32_RTC_TR_HOUR_SHIFT;
> +
> +	tm->tm_mday = (dr & STM32_RTC_DR_DATE) >> STM32_RTC_DR_DATE_SHIFT;
> +	tm->tm_mon = (dr & STM32_RTC_DR_MONTH) >> STM32_RTC_DR_MONTH_SHIFT;
> +	tm->tm_year = (dr & STM32_RTC_DR_YEAR) >> STM32_RTC_DR_YEAR_SHIFT;
> +	tm->tm_wday = (dr & STM32_RTC_DR_WDAY) >> STM32_RTC_DR_WDAY_SHIFT;
> +
> +	/* We don't report tm_yday and tm_isdst */
> +
> +	bcd2tm(tm);
> +
> +	if (rtc_valid_tm(tm) < 0) {
> +		dev_err(dev, "%s: rtc_time is not valid.\n", __func__);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +static int stm32_rtc_set_time(struct device *dev, struct rtc_time *tm)
> +{
> +	struct stm32_rtc *rtc = dev_get_drvdata(dev);
> +	unsigned int tr, dr;
> +	unsigned long irqflags;
> +	int ret = 0;
> +
> +	if (rtc_valid_tm(tm) < 0) {
> +		dev_err(dev, "%s: rtc_time is not valid.\n", __func__);
> +		return -EINVAL;
> +	}
> +
> +	tm2bcd(tm);
> +
> +	/* Time in BCD format */
> +	tr = ((tm->tm_sec << STM32_RTC_TR_SEC_SHIFT) & STM32_RTC_TR_SEC) |
> +	     ((tm->tm_min << STM32_RTC_TR_MIN_SHIFT) & STM32_RTC_TR_MIN) |
> +	     ((tm->tm_hour << STM32_RTC_TR_HOUR_SHIFT) & STM32_RTC_TR_HOUR);
> +
> +	/* Date in BCD format */
> +	dr = ((tm->tm_mday << STM32_RTC_DR_DATE_SHIFT) & STM32_RTC_DR_DATE) |
> +	     ((tm->tm_mon << STM32_RTC_DR_MONTH_SHIFT) & STM32_RTC_DR_MONTH) |
> +	     ((tm->tm_year << STM32_RTC_DR_YEAR_SHIFT) & STM32_RTC_DR_YEAR) |
> +	     ((tm->tm_wday << STM32_RTC_DR_WDAY_SHIFT) & STM32_RTC_DR_WDAY);
> +
> +	spin_lock_irqsave(&rtc->lock, irqflags);
> +
> +	stm32_rtc_wpr_unlock(rtc);
> +
> +	ret = stm32_rtc_enter_init_mode(rtc);
> +	if (ret) {
> +		dev_err(dev, "Can't enter in init mode. Set time aborted.\n");
> +		goto end;
> +	}
> +
> +	stm32_rtc_writel(rtc, STM32_RTC_TR, tr);
> +	stm32_rtc_writel(rtc, STM32_RTC_DR, dr);
> +
> +	stm32_rtc_exit_init_mode(rtc);
> +
> +	ret = stm32_rtc_wait_sync(rtc);
> +end:
> +	stm32_rtc_wpr_lock(rtc);
> +
> +	spin_unlock_irqrestore(&rtc->lock, irqflags);
> +
> +	return ret;
> +}
> +
> +static int stm32_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
> +{
> +	struct stm32_rtc *rtc = dev_get_drvdata(dev);
> +	struct rtc_time *tm = &alrm->time;
> +	unsigned int alrmar, cr, isr;
> +	unsigned long irqflags;
> +
> +	spin_lock_irqsave(&rtc->lock, irqflags);
> +
> +	alrmar = stm32_rtc_readl(rtc, STM32_RTC_ALRMAR);
> +	cr = stm32_rtc_readl(rtc, STM32_RTC_CR);
> +	isr = stm32_rtc_readl(rtc, STM32_RTC_ISR);
> +
> +	spin_unlock_irqrestore(&rtc->lock, irqflags);
> +
> +	if (alrmar & STM32_RTC_ALRMXR_DATE_MASK) {
> +		/*
> +		 * Date/day don't care in Alarm comparison so alarm triggers
> +		 * every day
> +		 */
> +		tm->tm_mday = -1;
> +		tm->tm_wday = -1;
> +	} else {
> +		if (alrmar & STM32_RTC_ALRMXR_WDSEL) {
> +			/* Alarm is set to a day of week */
> +			tm->tm_mday = -1;
> +			tm->tm_wday = (alrmar & STM32_RTC_ALRMXR_WDAY) >>
> +				      STM32_RTC_ALRMXR_WDAY_SHIFT;
> +			tm->tm_wday %= 7;
> +		} else {
> +			/* Alarm is set to a day of month */
> +			tm->tm_wday = -1;
> +			tm->tm_mday = (alrmar & STM32_RTC_ALRMXR_DATE) >>
> +				       STM32_RTC_ALRMXR_DATE_SHIFT;
> +		}
> +	}
> +
> +	if (alrmar & STM32_RTC_ALRMXR_HOUR_MASK) {
> +		/* Hours don't care in Alarm comparison */
> +		tm->tm_hour = -1;
> +	} else {
> +		tm->tm_hour = (alrmar & STM32_RTC_ALRMXR_HOUR) >>
> +			       STM32_RTC_ALRMXR_HOUR_SHIFT;
> +		if (alrmar & STM32_RTC_ALRMXR_PM)
> +			tm->tm_hour += 12;
> +	}
> +
> +	if (alrmar & STM32_RTC_ALRMXR_MIN_MASK) {
> +		/* Minutes don't care in Alarm comparison */
> +		tm->tm_min = -1;
> +	} else {
> +		tm->tm_min = (alrmar & STM32_RTC_ALRMXR_MIN) >>
> +			      STM32_RTC_ALRMXR_MIN_SHIFT;
> +	}
> +
> +	if (alrmar & STM32_RTC_ALRMXR_SEC_MASK) {
> +		/* Seconds don't care in Alarm comparison */
> +		tm->tm_sec = -1;
> +	} else {
> +		tm->tm_sec = (alrmar & STM32_RTC_ALRMXR_SEC) >>
> +			      STM32_RTC_ALRMXR_SEC_SHIFT;
> +	}
> +
> +	bcd2tm(tm);
> +
> +	alrm->enabled = (cr & STM32_RTC_CR_ALRAE) ? 1 : 0;
> +	alrm->pending = (isr & STM32_RTC_ISR_ALRAF) ? 1 : 0;
> +
> +	return 0;
> +}
> +
> +static int stm32_rtc_alarm_irq_enable(struct device *dev, unsigned int enabled)
> +{
> +	struct stm32_rtc *rtc = dev_get_drvdata(dev);
> +	unsigned long irqflags;
> +	unsigned int isr, cr;
> +
> +	cr = stm32_rtc_readl(rtc, STM32_RTC_CR);

Is the STM32_RTC_CR garanteed to be valid, i.e updated atomically?  If not this
should probably be below the spinlock. 

> +
> +	spin_lock_irqsave(&rtc->lock, irqflags);
> +
> +	stm32_rtc_wpr_unlock(rtc);
> +
> +	/* We expose Alarm A to the kernel */
> +	if (enabled)
> +		cr |= (STM32_RTC_CR_ALRAIE | STM32_RTC_CR_ALRAE);
> +	else
> +		cr &= ~(STM32_RTC_CR_ALRAIE | STM32_RTC_CR_ALRAE);
> +	stm32_rtc_writel(rtc, STM32_RTC_CR, cr);
> +
> +	/* Clear event irqflags, otherwise new events won't be received */
> +	isr = stm32_rtc_readl(rtc, STM32_RTC_ISR);
> +	isr &= ~STM32_RTC_ISR_ALRAF;
> +	stm32_rtc_writel(rtc, STM32_RTC_ISR, isr);
> +
> +	stm32_rtc_wpr_lock(rtc);
> +
> +	spin_unlock_irqrestore(&rtc->lock, irqflags);
> +
> +	return 0;
> +}
> +
> +static int stm32_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
> +{
> +	struct stm32_rtc *rtc = dev_get_drvdata(dev);
> +	struct rtc_time *tm = &alrm->time;
> +	unsigned long irqflags;
> +	unsigned int cr, isr, alrmar;
> +	int ret = 0;
> +
> +	if (rtc_valid_tm(tm)) {
> +		dev_err(dev, "Alarm time not valid.\n");
> +		return -EINVAL;
> +	}
> +
> +	tm2bcd(tm);
> +
> +	spin_lock_irqsave(&rtc->lock, irqflags);
> +
> +	stm32_rtc_wpr_unlock(rtc);
> +
> +	/* Disable Alarm */
> +	cr = stm32_rtc_readl(rtc, STM32_RTC_CR);
> +	cr &= ~STM32_RTC_CR_ALRAE;
> +	stm32_rtc_writel(rtc, STM32_RTC_CR, cr);
> +
> +	/* Poll Alarm write flag to be sure that Alarm update is allowed */
> +	ret = readl_relaxed_poll_timeout_atomic(rtc->base + STM32_RTC_ISR,
> +						isr,
> +						(isr & STM32_RTC_ISR_ALRAWF),
> +						10, 100);
> +
> +	if (ret) {
> +		dev_err(dev, "Alarm update not allowed\n");
> +		goto end;
> +	}
> +
> +	alrmar = 0;
> +
> +	if (tm->tm_mday < 0 && tm->tm_wday < 0) {
> +		/*
> +		 * Date/day don't care in Alarm comparison so alarm triggers
> +		 * every day
> +		 */
> +		alrmar |= STM32_RTC_ALRMXR_DATE_MASK;
> +	} else {
> +		if (tm->tm_mday > 0) {
> +			/* Date is selected (ignoring wday) */
> +			alrmar |= (tm->tm_mday << STM32_RTC_ALRMXR_DATE_SHIFT) &
> +				  STM32_RTC_ALRMXR_DATE;
> +		} else {
> +			/* Day of week is selected */
> +			int wday = (tm->tm_wday == 0) ? 7 : tm->tm_wday;
> +
> +			alrmar |= STM32_RTC_ALRMXR_WDSEL;
> +			alrmar |= (wday << STM32_RTC_ALRMXR_WDAY_SHIFT) &
> +				  STM32_RTC_ALRMXR_WDAY;
> +		}
> +	}
> +
> +	if (tm->tm_hour < 0) {
> +		/* Hours don't care in Alarm comparison */
> +		alrmar |= STM32_RTC_ALRMXR_HOUR_MASK;
> +	} else {
> +		/* 24-hour format */
> +		alrmar &= ~STM32_RTC_ALRMXR_PM;
> +		alrmar |= (tm->tm_hour << STM32_RTC_ALRMXR_HOUR_SHIFT) &
> +			  STM32_RTC_ALRMXR_HOUR;
> +	}
> +
> +	if (tm->tm_min < 0) {
> +		/* Minutes don't care in Alarm comparison */
> +		alrmar |= STM32_RTC_ALRMXR_MIN_MASK;
> +	} else {
> +		alrmar |= (tm->tm_min << STM32_RTC_ALRMXR_MIN_SHIFT) &
> +			  STM32_RTC_ALRMXR_MIN;
> +	}
> +
> +	if (tm->tm_sec < 0) {
> +		/* Seconds don't care in Alarm comparison */
> +		alrmar |= STM32_RTC_ALRMXR_SEC_MASK;
> +	} else {
> +		alrmar |= (tm->tm_sec << STM32_RTC_ALRMXR_SEC_SHIFT) &
> +			  STM32_RTC_ALRMXR_SEC;
> +	}
> +
> +	/* Write to Alarm register */
> +	stm32_rtc_writel(rtc, STM32_RTC_ALRMAR, alrmar);
> +
> +	if (alrm->enabled)
> +		stm32_rtc_alarm_irq_enable(dev, 1);
> +	else
> +		stm32_rtc_alarm_irq_enable(dev, 0);
> +
> +end:
> +	stm32_rtc_wpr_lock(rtc);
> +
> +	spin_unlock_irqrestore(&rtc->lock, irqflags);
> +
> +	return ret;
> +}
> +
> +static const struct rtc_class_ops stm32_rtc_ops = {
> +	.read_time	= stm32_rtc_read_time,
> +	.set_time	= stm32_rtc_set_time,
> +	.read_alarm	= stm32_rtc_read_alarm,
> +	.set_alarm	= stm32_rtc_set_alarm,
> +	.alarm_irq_enable = stm32_rtc_alarm_irq_enable,
> +};
> +
> +#ifdef CONFIG_OF
> +static const struct of_device_id stm32_rtc_of_match[] = {
> +	{ .compatible = "st,stm32-rtc" },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(of, stm32_rtc_of_match);
> +#endif
> +
> +static int stm32_rtc_init(struct platform_device *pdev,
> +			  struct stm32_rtc *rtc)
> +{
> +	unsigned int prer, pred_a, pred_s, pred_a_max, pred_s_max, cr;
> +	unsigned int rate;
> +	unsigned long irqflags;
> +	int ret = 0;
> +
> +	rate = clk_get_rate(rtc->ck_rtc);
> +
> +	/* Find prediv_a and prediv_s to obtain the 1Hz calendar clock */
> +	pred_a_max = STM32_RTC_PRER_PRED_A >> STM32_RTC_PRER_PRED_A_SHIFT;
> +	pred_s_max = STM32_RTC_PRER_PRED_S >> STM32_RTC_PRER_PRED_S_SHIFT;
> +
> +	for (pred_a = pred_a_max; pred_a >= 0; pred_a--) {
> +		pred_s = (rate / (pred_a + 1)) - 1;
> +
> +		if (((pred_s + 1) * (pred_a + 1)) == rate)
> +			break;
> +	}
> +
> +	/*
> +	 * Can't find a 1Hz, so give priority to RTC power consumption
> +	 * by choosing the higher possible value for prediv_a
> +	 */
> +	if ((pred_s > pred_s_max) || (pred_a > pred_a_max)) {
> +		pred_a = pred_a_max;
> +		pred_s = (rate / (pred_a + 1)) - 1;
> +
> +		dev_warn(&pdev->dev, "ck_rtc is %s\n",
> +			 (rate - ((pred_a + 1) * (pred_s + 1)) < 0) ?
> +			 "fast" : "slow");
> +	}
> +
> +	spin_lock_irqsave(&rtc->lock, irqflags);
> +
> +	stm32_rtc_wpr_unlock(rtc);
> +
> +	ret = stm32_rtc_enter_init_mode(rtc);
> +	if (ret) {
> +		dev_err(&pdev->dev,
> +			"Can't enter in init mode. Prescaler config failed.\n");
> +		goto end;
> +	}
> +
> +	prer = (pred_s << STM32_RTC_PRER_PRED_S_SHIFT) & STM32_RTC_PRER_PRED_S;
> +	stm32_rtc_writel(rtc, STM32_RTC_PRER, prer);
> +	prer |= (pred_a << STM32_RTC_PRER_PRED_A_SHIFT) & STM32_RTC_PRER_PRED_A;
> +	stm32_rtc_writel(rtc, STM32_RTC_PRER, prer);
> +
> +	/* Force 24h time format */
> +	cr = stm32_rtc_readl(rtc, STM32_RTC_CR);
> +	cr &= ~STM32_RTC_CR_FMT;
> +	stm32_rtc_writel(rtc, STM32_RTC_CR, cr);
> +
> +	stm32_rtc_exit_init_mode(rtc);
> +
> +	ret = stm32_rtc_wait_sync(rtc);
> +
> +	if (stm32_rtc_readl(rtc, STM32_RTC_ISR) & STM32_RTC_ISR_INITS)
> +		dev_warn(&pdev->dev, "Date/Time must be initialized\n");
> +end:
> +	stm32_rtc_wpr_lock(rtc);
> +
> +	spin_unlock_irqrestore(&rtc->lock, irqflags);
> +
> +	return ret;
> +}
> +
> +static int stm32_rtc_probe(struct platform_device *pdev)
> +{
> +	struct stm32_rtc *rtc;
> +	struct resource *res;
> +	int ret;
> +
> +	rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL);
> +	if (!rtc)
> +		return -ENOMEM;
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);

The value of 'res' should be checked before using it.

> +	rtc->base = devm_ioremap_resource(&pdev->dev, res);
> +	if (IS_ERR(rtc->base))
> +		return PTR_ERR(rtc->base);
> +
> +	dbp = syscon_regmap_lookup_by_phandle(pdev->dev.of_node, "st,syscfg");
> +	if (IS_ERR(dbp)) {
> +		dev_err(&pdev->dev, "no st,syscfg\n");
> +		return PTR_ERR(dbp);
> +	}
> +
> +	spin_lock_init(&rtc->lock);
> +
> +	rtc->ck_rtc = devm_clk_get(&pdev->dev, "ck_rtc");
> +	if (IS_ERR(rtc->ck_rtc)) {
> +		dev_err(&pdev->dev, "no ck_rtc clock");
> +		return PTR_ERR(rtc->ck_rtc);
> +	}
> +
> +	ret = clk_prepare_enable(rtc->ck_rtc);
> +	if (ret)
> +		return ret;
> +
> +	if (dbp)
> +		regmap_update_bits(dbp, PWR_CR, PWR_CR_DBP, PWR_CR_DBP);

The code above exits if there is a problem with the dbp, there is no point in
checking again.

> +
> +	ret = stm32_rtc_init(pdev, rtc);
> +	if (ret)
> +		goto err;
> +
> +	rtc->irq_alarm = platform_get_irq_byname(pdev, "alarm");
> +	if (rtc->irq_alarm <= 0) {
> +		dev_err(&pdev->dev, "no alarm irq\n");
> +		ret = -ENOENT;
> +		goto err;
> +	}
> +
> +	platform_set_drvdata(pdev, rtc);
> +
> +	device_init_wakeup(&pdev->dev, true);

What happens if device_init_wakeup() returns an error?

> +
> +	rtc->rtc_dev = devm_rtc_device_register(&pdev->dev, pdev->name,
> +			&stm32_rtc_ops, THIS_MODULE);
> +	if (IS_ERR(rtc->rtc_dev)) {
> +		ret = PTR_ERR(rtc->rtc_dev);
> +		dev_err(&pdev->dev, "rtc device registration failed, err=%d\n",
> +			ret);
> +		goto err;
> +	}
> +
> +	/* Handle RTC alarm interrupts */
> +	ret = devm_request_irq(&pdev->dev, rtc->irq_alarm,
> +			       stm32_rtc_alarm_irq, IRQF_TRIGGER_RISING,
> +			       dev_name(&rtc->rtc_dev->dev), rtc);
> +	if (ret) {
> +		dev_err(&pdev->dev, "IRQ%d (alarm interrupt) already claimed\n",
> +			rtc->irq_alarm);
> +		goto err;
> +	}
> +
> +	return 0;
> +err:
> +	clk_disable_unprepare(rtc->ck_rtc);
> +
> +	if (dbp)
> +		regmap_update_bits(dbp, PWR_CR, PWR_CR_DBP, ~PWR_CR_DBP);

Same comment as above.

> +
> +	device_init_wakeup(&pdev->dev, false);
> +
> +	return ret;
> +}
> +
> +static int __exit stm32_rtc_remove(struct platform_device *pdev)
> +{
> +	struct stm32_rtc *rtc = platform_get_drvdata(pdev);
> +	unsigned int cr;
> +
> +	/* Disable interrupts */
> +	stm32_rtc_wpr_unlock(rtc);
> +	cr = stm32_rtc_readl(rtc, STM32_RTC_CR);
> +	cr &= ~STM32_RTC_CR_ALRAIE;
> +	stm32_rtc_writel(rtc, STM32_RTC_CR, cr);
> +	stm32_rtc_wpr_lock(rtc);
> +
> +	clk_disable_unprepare(rtc->ck_rtc);
> +
> +	/* Enable backup domain write protection */
> +	if (dbp)
> +		regmap_update_bits(dbp, PWR_CR, PWR_CR_DBP, ~PWR_CR_DBP);
> +
> +	device_init_wakeup(&pdev->dev, false);
> +
> +	return 0;
> +}
> +
> +#ifdef CONFIG_PM_SLEEP
> +static int stm32_rtc_suspend(struct device *dev)
> +{
> +	struct stm32_rtc *rtc = dev_get_drvdata(dev);
> +
> +	if (device_may_wakeup(dev))
> +		return enable_irq_wake(rtc->irq_alarm);
> +
> +	return 0;
> +}
> +
> +static int stm32_rtc_resume(struct device *dev)
> +{
> +	struct stm32_rtc *rtc = dev_get_drvdata(dev);
> +	int ret = 0;
> +
> +	ret = stm32_rtc_wait_sync(rtc);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (device_may_wakeup(dev))
> +		return disable_irq_wake(rtc->irq_alarm);
> +
> +	return ret;
> +}
> +#endif
> +
> +static SIMPLE_DEV_PM_OPS(stm32_rtc_pm_ops,
> +			 stm32_rtc_suspend, stm32_rtc_resume);
> +
> +static struct platform_driver stm32_rtc_driver = {
> +	.probe		= stm32_rtc_probe,
> +	.remove		= stm32_rtc_remove,
> +	.driver		= {
> +		.name	= DRIVER_NAME,
> +		.pm	= &stm32_rtc_pm_ops,
> +		.of_match_table = stm32_rtc_of_match,
> +	},
> +};
> +
> +module_platform_driver(stm32_rtc_driver);
> +
> +MODULE_ALIAS("platform:" DRIVER_NAME);
> +MODULE_AUTHOR("Amelie Delaunay <amelie.delaunay@...com>");
> +MODULE_DESCRIPTION("STMicroelectronics STM32 Real Time Clock driver");
> +MODULE_LICENSE("GPL v2");
> -- 
> 1.9.1
> 

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