rtc: at91sam9: make use of syscon/regmap to access GPBR registers

The GPBR registers are not part of the RTT block and thus should not be
defined in the reg property of the rtt node.

Use syscon to provide a proper DT representation and reference the GPBR
syscon device in a new "atmel,rtt-rtc-time-reg" property which store both
the syscon device phandle and the register offset within the GPBR block.

When using non DT boards, we won't be able to retrieve the syscon regmap,
hence we need to create our own regmap using the memory region defined
in the 2nd memory resource assigned to the RTT platform device.

Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Johan Hovold <johan@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

drivers/rtc/Kconfig

@@ -1111,6 +1111,7 @@ config RTC_DRV_AT91RM9200
 config RTC_DRV_AT91SAM9
 	tristate "AT91SAM9x/AT91CAP9 RTT as RTC"
 	depends on ARCH_AT91 && !(ARCH_AT91RM9200 || ARCH_AT91X40)
+	select MFD_SYSCON
 	help
 	  RTC driver for the Atmel AT91SAM9x and AT91CAP9 internal RTT
 	  (Real Time Timer). These timers are powered by the backup power

drivers/rtc/rtc-at91sam9.c

@@ -21,6 +21,8 @@
 #include <linux/slab.h>
 #include <linux/platform_data/atmel.h>
 #include <linux/io.h>
+#include <linux/mfd/syscon.h>
+#include <linux/regmap.h>
 
 /*
  * This driver uses two configurable hardware resources that live in the
@@ -72,7 +74,8 @@ struct sam9_rtc {
 	void __iomem		*rtt;
 	struct rtc_device	*rtcdev;
 	u32			imr;
-	void __iomem		*gpbr;
+	struct regmap		*gpbr;
+	unsigned int		gpbr_offset;
 	int 			irq;
 };
 
@@ -81,10 +84,19 @@ struct sam9_rtc {
 #define rtt_writel(rtc, field, val) \
 	writel((val), (rtc)->rtt + AT91_RTT_ ## field)
 
-#define gpbr_readl(rtc) \
-	readl((rtc)->gpbr)
-#define gpbr_writel(rtc, val) \
-	writel((val), (rtc)->gpbr)
+static inline unsigned int gpbr_readl(struct sam9_rtc *rtc)
+{
+	unsigned int val;
+
+	regmap_read(rtc->gpbr, rtc->gpbr_offset, &val);
+
+	return val;
+}
+
+static inline void gpbr_writel(struct sam9_rtc *rtc, unsigned int val)
+{
+	regmap_write(rtc->gpbr, rtc->gpbr_offset, val);
+}
 
 /*
  * Read current time and date in RTC
@@ -301,6 +313,12 @@ static const struct rtc_class_ops at91_rtc_ops = {
 	.alarm_irq_enable = at91_rtc_alarm_irq_enable,
 };
 
+static struct regmap_config gpbr_regmap_config = {
+	.reg_bits = 32,
+	.val_bits = 32,
+	.reg_stride = 4,
+};
+
 /*
  * Initialize and install RTC driver
  */
@@ -334,10 +352,38 @@ static int at91_rtc_probe(struct platform_device *pdev)
 	if (IS_ERR(rtc->rtt))
 		return PTR_ERR(rtc->rtt);
 
-	r = platform_get_resource(pdev, IORESOURCE_MEM, 1);
-	rtc->gpbr = devm_ioremap_resource(&pdev->dev, r);
-	if (IS_ERR(rtc->gpbr))
-		return PTR_ERR(rtc->rtt);
+	if (!pdev->dev.of_node) {
+		/*
+		 * TODO: Remove this code chunk when removing non DT board
+		 * support. Remember to remove the gpbr_regmap_config
+		 * variable too.
+		 */
+		void __iomem *gpbr;
+
+		r = platform_get_resource(pdev, IORESOURCE_MEM, 1);
+		gpbr = devm_ioremap_resource(&pdev->dev, r);
+		if (IS_ERR(gpbr))
+			return PTR_ERR(gpbr);
+
+		rtc->gpbr = regmap_init_mmio(NULL, gpbr,
+					     &gpbr_regmap_config);
+	} else {
+		struct of_phandle_args args;
+
+		ret = of_parse_phandle_with_fixed_args(pdev->dev.of_node,
+						"atmel,rtt-rtc-time-reg", 1, 0,
+						&args);
+		if (ret)
+			return ret;
+
+		rtc->gpbr = syscon_node_to_regmap(args.np);
+		rtc->gpbr_offset = args.args[0];
+	}
+
+	if (IS_ERR(rtc->gpbr)) {
+		dev_err(&pdev->dev, "failed to retrieve gpbr regmap, aborting.\n");
+		return -ENOMEM;
+	}
 
 	mr = rtt_readl(rtc, MR);