drivers/rtc/rtc-at91rm9200.c: use a variable for storing IMR

On some revisions of AT91 SoCs, the RTC IMR register is not working.
Instead of elaborating a workaround for that specific SoC or IP version,
we simply use a software variable to store the Interrupt Mask Register
and modify it for each enabling/disabling of an interrupt. The overhead
of this is negligible anyway.

The interrupt mask register (IMR) for the RTC is broken on the AT91SAM9x5
sub-family of SoCs (good overview of the members here:
http://www.eewiki.net/display/linuxonarm/AT91SAM9x5 ). The "user visible
effect" is the RTC doesn't work.

That sub-family is less than two years old and only has devicetree (DT)
support and came online circa lk 3.7 . The dust is yet to settle on the
DT stuff at least for AT91 SoCs (translation: lots of stuff is still
broken, so much that it is hard to know where to start).

The fix in the patch is pretty simple: just shadow the silicon IMR
register with a variable in the driver. Some older SoCs (pre-DT) use the
the rtc-at91rm9200 driver (e.g. obviously the AT91RM9200) and they should
not be impacted by the change. There shouldn't be a large volume of
interrupts associated with a RTC.

Signed-off-by: Nicolas Ferre <[e-mail]>
Reported-by: Douglas Gilbert <[e-mail]>
Cc: Jean-Christophe PLAGNIOL-VILLARD <[e-mail]>
Cc: Ludovic Desroches <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/rtc/rtc-at91rm9200.c

···
 static unsigned int at91_alarm_year = AT91_RTC_EPOCH;
 static void __iomem *at91_rtc_regs;
 static int irq;
+static u32 at91_rtc_imr;
 
 /*
  * Decode time/date into rtc_time structure
···
 	cr = at91_rtc_read(AT91_RTC_CR);
 	at91_rtc_write(AT91_RTC_CR, cr | AT91_RTC_UPDCAL | AT91_RTC_UPDTIM);
 
+	at91_rtc_imr |= AT91_RTC_ACKUPD;
 	at91_rtc_write(AT91_RTC_IER, AT91_RTC_ACKUPD);
 	wait_for_completion(&at91_rtc_updated);	/* wait for ACKUPD interrupt */
 	at91_rtc_write(AT91_RTC_IDR, AT91_RTC_ACKUPD);
+	at91_rtc_imr &= ~AT91_RTC_ACKUPD;
 
 	at91_rtc_write(AT91_RTC_TIMR,
 			  bin2bcd(tm->tm_sec) << 0
···
 	tm->tm_yday = rtc_year_days(tm->tm_mday, tm->tm_mon, tm->tm_year);
 	tm->tm_year = at91_alarm_year - 1900;
 
-	alrm->enabled = (at91_rtc_read(AT91_RTC_IMR) & AT91_RTC_ALARM)
+	alrm->enabled = (at91_rtc_imr & AT91_RTC_ALARM)
 			? 1 : 0;
 
 	dev_dbg(dev, "%s(): %4d-%02d-%02d %02d:%02d:%02d\n", __func__,
···
 	tm.tm_sec = alrm->time.tm_sec;
 
 	at91_rtc_write(AT91_RTC_IDR, AT91_RTC_ALARM);
+	at91_rtc_imr &= ~AT91_RTC_ALARM;
 	at91_rtc_write(AT91_RTC_TIMALR,
 		  bin2bcd(tm.tm_sec) << 0
 		| bin2bcd(tm.tm_min) << 8
···
 
 	if (alrm->enabled) {
 		at91_rtc_write(AT91_RTC_SCCR, AT91_RTC_ALARM);
+		at91_rtc_imr |= AT91_RTC_ALARM;
 		at91_rtc_write(AT91_RTC_IER, AT91_RTC_ALARM);
 	}
 
···
 
 	if (enabled) {
 		at91_rtc_write(AT91_RTC_SCCR, AT91_RTC_ALARM);
+		at91_rtc_imr |= AT91_RTC_ALARM;
 		at91_rtc_write(AT91_RTC_IER, AT91_RTC_ALARM);
-	} else
+	} else {
 		at91_rtc_write(AT91_RTC_IDR, AT91_RTC_ALARM);
+		at91_rtc_imr &= ~AT91_RTC_ALARM;
+	}
 
 	return 0;
 }
···
  */
 static int at91_rtc_proc(struct device *dev, struct seq_file *seq)
 {
-	unsigned long imr = at91_rtc_read(AT91_RTC_IMR);
-
 	seq_printf(seq, "update_IRQ\t: %s\n",
-			(imr & AT91_RTC_ACKUPD) ? "yes" : "no");
+			(at91_rtc_imr & AT91_RTC_ACKUPD) ? "yes" : "no");
 	seq_printf(seq, "periodic_IRQ\t: %s\n",
-			(imr & AT91_RTC_SECEV) ? "yes" : "no");
+			(at91_rtc_imr & AT91_RTC_SECEV) ? "yes" : "no");
 
 	return 0;
 }
···
 	unsigned int rtsr;
 	unsigned long events = 0;
 
-	rtsr = at91_rtc_read(AT91_RTC_SR) & at91_rtc_read(AT91_RTC_IMR);
+	rtsr = at91_rtc_read(AT91_RTC_SR) & at91_rtc_imr;
 	if (rtsr) {		/* this interrupt is shared!  Is it ours? */
 		if (rtsr & AT91_RTC_ALARM)
 			events |= (RTC_AF | RTC_IRQF);
···
 	at91_rtc_write(AT91_RTC_IDR, AT91_RTC_ACKUPD | AT91_RTC_ALARM |
 					AT91_RTC_SECEV | AT91_RTC_TIMEV |
 					AT91_RTC_CALEV);
+	at91_rtc_imr = 0;
 
 	ret = request_irq(irq, at91_rtc_interrupt,
 				IRQF_SHARED,
···
 	at91_rtc_write(AT91_RTC_IDR, AT91_RTC_ACKUPD | AT91_RTC_ALARM |
 					AT91_RTC_SECEV | AT91_RTC_TIMEV |
 					AT91_RTC_CALEV);
+	at91_rtc_imr = 0;
 	free_irq(irq, pdev);
 
 	rtc_device_unregister(rtc);
···
 
 /* AT91RM9200 RTC Power management control */
 
-static u32 at91_rtc_imr;
+static u32 at91_rtc_bkpimr;
+
 
 static int at91_rtc_suspend(struct device *dev)
 {
 	/* this IRQ is shared with DBGU and other hardware which isn't
 	 * necessarily doing PM like we are...
 	 */
-	at91_rtc_imr = at91_rtc_read(AT91_RTC_IMR)
-			& (AT91_RTC_ALARM|AT91_RTC_SECEV);
-	if (at91_rtc_imr) {
-		if (device_may_wakeup(dev))
+	at91_rtc_bkpimr = at91_rtc_imr & (AT91_RTC_ALARM|AT91_RTC_SECEV);
+	if (at91_rtc_bkpimr) {
+		if (device_may_wakeup(dev)) {
 			enable_irq_wake(irq);
-		else
-			at91_rtc_write(AT91_RTC_IDR, at91_rtc_imr);
-	}
+		} else {
+			at91_rtc_write(AT91_RTC_IDR, at91_rtc_bkpimr);
+			at91_rtc_imr &= ~at91_rtc_bkpimr;
+		}
+}
 	return 0;
 }
 
 static int at91_rtc_resume(struct device *dev)
 {
-	if (at91_rtc_imr) {
-		if (device_may_wakeup(dev))
+	if (at91_rtc_bkpimr) {
+		if (device_may_wakeup(dev)) {
 			disable_irq_wake(irq);
-		else
-			at91_rtc_write(AT91_RTC_IER, at91_rtc_imr);
+		} else {
+			at91_rtc_imr |= at91_rtc_bkpimr;
+			at91_rtc_write(AT91_RTC_IER, at91_rtc_bkpimr);
+		}
 	}
 	return 0;
 }

drivers/rtc/rtc-at91rm9200.h

···
 #define	AT91_RTC_SCCR		0x1c			/* Status Clear Command Register */
 #define	AT91_RTC_IER		0x20			/* Interrupt Enable Register */
 #define	AT91_RTC_IDR		0x24			/* Interrupt Disable Register */
-#define	AT91_RTC_IMR		0x28			/* Interrupt Mask Register */
 
 #define	AT91_RTC_VER		0x2c			/* Valid Entry Register */
 #define		AT91_RTC_NVTIM		(1 <<  0)		/* Non valid Time */