[PATCH] use rtc_lock to protect RTC operations

[PATCH] use rtc_lock to protect RTC operations

[Atsushi Nemoto]

Many RTC routines are not protected each other.  There are potential
race, for example, ntp-update and /dev/rtc.  This patch fixes them
using rtc_lock.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>

diff --git a/arch/mips/ddb5xxx/common/rtc_ds1386.c b/arch/mips/ddb5xxx/common/rtc_ds1386.c
--- a/arch/mips/ddb5xxx/common/rtc_ds1386.c
+++ b/arch/mips/ddb5xxx/common/rtc_ds1386.c
@@ -41,7 +41,9 @@ rtc_ds1386_get_time(void)
 	u8 byte;
 	u8 temp;
 	unsigned int year, month, day, hour, minute, second;
+	unsigned long flags;
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	/* let us freeze external registers */
 	byte = READ_RTC(0xB);
 	byte &= 0x3f;
@@ -60,6 +62,7 @@ rtc_ds1386_get_time(void)
 	/* enable time transfer */
 	byte |= 0x80;
 	WRITE_RTC(0xB, byte);
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	/* calc hour */
 	if (temp & 0x40) {
@@ -81,7 +84,9 @@ rtc_ds1386_set_time(unsigned long t)
 	u8 byte;
 	u8 temp;
 	u8 year, month, day, hour, minute, second;
+	unsigned long flags;
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	/* let us freeze external registers */
 	byte = READ_RTC(0xB);
 	byte &= 0x3f;
@@ -133,6 +138,7 @@ rtc_ds1386_set_time(unsigned long t)
 	if (second != READ_RTC(0x1)) {
 		WRITE_RTC(0x1, second);
 	}
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	return 0;
 }
diff --git a/arch/mips/dec/time.c b/arch/mips/dec/time.c
--- a/arch/mips/dec/time.c
+++ b/arch/mips/dec/time.c
@@ -37,10 +37,25 @@
 #include <asm/dec/machtype.h>
 
 
+/*
+ * Returns true if a clock update is in progress
+ */
+static inline unsigned char dec_rtc_is_updating(void)
+{
+	unsigned char uip;
+	unsigned long flags;
+
+	spin_lock_irqsave(&rtc_lock, flags);
+	uip = (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP);
+	spin_unlock_irqrestore(&rtc_lock, flags);
+	return uip;
+}
+
 static unsigned long dec_rtc_get_time(void)
 {
 	unsigned int year, mon, day, hour, min, sec, real_year;
 	int i;
+	unsigned long flags;
 
 	/* The Linux interpretation of the DS1287 clock register contents:
 	 * When the Update-In-Progress (UIP) flag goes from 1 to 0, the
@@ -49,11 +64,12 @@ static unsigned long dec_rtc_get_time(vo
 	 */
 	/* read RTC exactly on falling edge of update flag */
 	for (i = 0; i < 1000000; i++)	/* may take up to 1 second... */
-		if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP)
+		if (dec_rtc_is_updating())
 			break;
 	for (i = 0; i < 1000000; i++)	/* must try at least 2.228 ms */
-		if (!(CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP))
+		if (!dec_rtc_is_updating())
 			break;
+	spin_lock_irqsave(&rtc_lock, flags);
 	/* Isn't this overkill?  UIP above should guarantee consistency */
 	do {
 		sec = CMOS_READ(RTC_SECONDS);
@@ -77,6 +93,7 @@ static unsigned long dec_rtc_get_time(vo
 	 * of unused BBU RAM locations.
 	 */
 	real_year = CMOS_READ(RTC_DEC_YEAR);
+	spin_unlock_irqrestore(&rtc_lock, flags);
 	year += real_year - 72 + 2000;
 
 	return mktime(year, mon, day, hour, min, sec);
@@ -95,6 +112,8 @@ static int dec_rtc_set_mmss(unsigned lon
 	int real_seconds, real_minutes, cmos_minutes;
 	unsigned char save_control, save_freq_select;
 
+	/* irq are locally disabled here */
+	spin_lock(&rtc_lock);
 	/* tell the clock it's being set */
 	save_control = CMOS_READ(RTC_CONTROL);
 	CMOS_WRITE((save_control | RTC_SET), RTC_CONTROL);
@@ -141,6 +160,7 @@ static int dec_rtc_set_mmss(unsigned lon
 	 */
 	CMOS_WRITE(save_control, RTC_CONTROL);
 	CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
+	spin_unlock(&rtc_lock);
 
 	return retval;
 }
diff --git a/arch/mips/jmr3927/common/rtc_ds1742.c b/arch/mips/jmr3927/common/rtc_ds1742.c
--- a/arch/mips/jmr3927/common/rtc_ds1742.c
+++ b/arch/mips/jmr3927/common/rtc_ds1742.c
@@ -57,7 +57,9 @@ rtc_ds1742_get_time(void)
 {
 	unsigned int year, month, day, hour, minute, second;
 	unsigned int century;
+	unsigned long flags;
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	CMOS_WRITE(RTC_READ, RTC_CONTROL);
 	second = BCD2BIN(CMOS_READ(RTC_SECONDS) & RTC_SECONDS_MASK);
 	minute = BCD2BIN(CMOS_READ(RTC_MINUTES));
@@ -67,6 +69,7 @@ rtc_ds1742_get_time(void)
 	year = BCD2BIN(CMOS_READ(RTC_YEAR));
 	century = BCD2BIN(CMOS_READ(RTC_CENTURY) & RTC_CENTURY_MASK);
 	CMOS_WRITE(0, RTC_CONTROL);
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	year += century * 100;
 
@@ -81,7 +84,9 @@ rtc_ds1742_set_time(unsigned long t)
 	u8 year, month, day, hour, minute, second;
 	u8 cmos_year, cmos_month, cmos_day, cmos_hour, cmos_minute, cmos_second;
 	int cmos_century;
+	unsigned long flags;
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	CMOS_WRITE(RTC_READ, RTC_CONTROL);
 	cmos_second = (u8)(CMOS_READ(RTC_SECONDS) & RTC_SECONDS_MASK);
 	cmos_minute = (u8)CMOS_READ(RTC_MINUTES);
@@ -139,6 +144,7 @@ rtc_ds1742_set_time(unsigned long t)
 
 	/* RTC_CENTURY and RTC_CONTROL share same address... */
 	CMOS_WRITE(cmos_century, RTC_CONTROL);
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	return 0;
 }
diff --git a/arch/mips/lasat/ds1603.c b/arch/mips/lasat/ds1603.c
--- a/arch/mips/lasat/ds1603.c
+++ b/arch/mips/lasat/ds1603.c
@@ -8,6 +8,7 @@
 #include <asm/lasat/lasat.h>
 #include <linux/delay.h>
 #include <asm/lasat/ds1603.h>
+#include <asm/time.h>
 
 #include "ds1603.h"
 
@@ -138,19 +139,27 @@ static void rtc_end_op(void)
 unsigned long ds1603_read(void)
 {
 	unsigned long word;
+	unsigned long flags;
+
+	spin_lock_irqsave(&rtc_lock, flags);
 	rtc_init_op();
 	rtc_write_byte(READ_TIME_CMD);
 	word = rtc_read_word();
 	rtc_end_op();
+	spin_unlock_irqrestore(&rtc_lock, flags);
 	return word;
 }
 
 int ds1603_set(unsigned long time)
 {
+	unsigned long flags;
+
+	spin_lock_irqsave(&rtc_lock, flags);
 	rtc_init_op();
 	rtc_write_byte(SET_TIME_CMD);
 	rtc_write_word(time);
 	rtc_end_op();
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	return 0;
 }
diff --git a/arch/mips/momentum/jaguar_atx/setup.c b/arch/mips/momentum/jaguar_atx/setup.c
--- a/arch/mips/momentum/jaguar_atx/setup.c
+++ b/arch/mips/momentum/jaguar_atx/setup.c
@@ -149,7 +149,9 @@ arch_initcall(per_cpu_mappings);
 unsigned long m48t37y_get_time(void)
 {
 	unsigned int year, month, day, hour, min, sec;
+	unsigned long flags;
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	/* stop the update */
 	rtc_base[0x7ff8] = 0x40;
 
@@ -166,6 +168,7 @@ unsigned long m48t37y_get_time(void)
 
 	/* start the update */
 	rtc_base[0x7ff8] = 0x00;
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	return mktime(year, month, day, hour, min, sec);
 }
@@ -173,11 +176,13 @@ unsigned long m48t37y_get_time(void)
 int m48t37y_set_time(unsigned long sec)
 {
 	struct rtc_time tm;
+	unsigned long flags;
 
 	/* convert to a more useful format -- note months count from 0 */
 	to_tm(sec, &tm);
 	tm.tm_mon += 1;
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	/* enable writing */
 	rtc_base[0x7ff8] = 0x80;
 
@@ -201,6 +206,7 @@ int m48t37y_set_time(unsigned long sec)
 
 	/* disable writing */
 	rtc_base[0x7ff8] = 0x00;
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	return 0;
 }
diff --git a/arch/mips/momentum/ocelot_3/setup.c b/arch/mips/momentum/ocelot_3/setup.c
--- a/arch/mips/momentum/ocelot_3/setup.c
+++ b/arch/mips/momentum/ocelot_3/setup.c
@@ -135,7 +135,9 @@ void setup_wired_tlb_entries(void)
 unsigned long m48t37y_get_time(void)
 {
 	unsigned int year, month, day, hour, min, sec;
+	unsigned long flags;
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	/* stop the update */
 	rtc_base[0x7ff8] = 0x40;
 
@@ -152,6 +154,7 @@ unsigned long m48t37y_get_time(void)
 
 	/* start the update */
 	rtc_base[0x7ff8] = 0x00;
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	return mktime(year, month, day, hour, min, sec);
 }
@@ -159,11 +162,13 @@ unsigned long m48t37y_get_time(void)
 int m48t37y_set_time(unsigned long sec)
 {
 	struct rtc_time tm;
+	unsigned long flags;
 
 	/* convert to a more useful format -- note months count from 0 */
 	to_tm(sec, &tm);
 	tm.tm_mon += 1;
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	/* enable writing */
 	rtc_base[0x7ff8] = 0x80;
 
@@ -187,6 +192,7 @@ int m48t37y_set_time(unsigned long sec)
 
 	/* disable writing */
 	rtc_base[0x7ff8] = 0x00;
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	return 0;
 }
diff --git a/arch/mips/momentum/ocelot_c/setup.c b/arch/mips/momentum/ocelot_c/setup.c
--- a/arch/mips/momentum/ocelot_c/setup.c
+++ b/arch/mips/momentum/ocelot_c/setup.c
@@ -140,7 +140,9 @@ unsigned long m48t37y_get_time(void)
 	unsigned char* rtc_base = (unsigned char*)0xfc800000;
 #endif
 	unsigned int year, month, day, hour, min, sec;
+	unsigned long flags;
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	/* stop the update */
 	rtc_base[0x7ff8] = 0x40;
 
@@ -157,6 +159,7 @@ unsigned long m48t37y_get_time(void)
 
 	/* start the update */
 	rtc_base[0x7ff8] = 0x00;
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	return mktime(year, month, day, hour, min, sec);
 }
@@ -169,11 +172,13 @@ int m48t37y_set_time(unsigned long sec)
 	unsigned char* rtc_base = (unsigned char*)0xfc800000;
 #endif
 	struct rtc_time tm;
+	unsigned long flags;
 
 	/* convert to a more useful format -- note months count from 0 */
 	to_tm(sec, &tm);
 	tm.tm_mon += 1;
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	/* enable writing */
 	rtc_base[0x7ff8] = 0x80;
 
@@ -197,6 +202,7 @@ int m48t37y_set_time(unsigned long sec)
 
 	/* disable writing */
 	rtc_base[0x7ff8] = 0x00;
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	return 0;
 }
diff --git a/arch/mips/pmc-sierra/yosemite/setup.c b/arch/mips/pmc-sierra/yosemite/setup.c
--- a/arch/mips/pmc-sierra/yosemite/setup.c
+++ b/arch/mips/pmc-sierra/yosemite/setup.c
@@ -73,7 +73,9 @@ void __init bus_error_init(void)
 unsigned long m48t37y_get_time(void)
 {
 	unsigned int year, month, day, hour, min, sec;
+	unsigned long flags;
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	/* Stop the update to the time */
 	m48t37_base->control = 0x40;
 
@@ -88,6 +90,7 @@ unsigned long m48t37y_get_time(void)
 
 	/* Start the update to the time again */
 	m48t37_base->control = 0x00;
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	return mktime(year, month, day, hour, min, sec);
 }
@@ -95,11 +98,13 @@ unsigned long m48t37y_get_time(void)
 int m48t37y_set_time(unsigned long sec)
 {
 	struct rtc_time tm;
+	unsigned long flags;
 
 	/* convert to a more useful format -- note months count from 0 */
 	to_tm(sec, &tm);
 	tm.tm_mon += 1;
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	/* enable writing */
 	m48t37_base->control = 0x80;
 
@@ -123,6 +128,7 @@ int m48t37y_set_time(unsigned long sec)
 
 	/* disable writing */
 	m48t37_base->control = 0x00;
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	return 0;
 }
diff --git a/arch/mips/sgi-ip22/ip22-time.c b/arch/mips/sgi-ip22/ip22-time.c
--- a/arch/mips/sgi-ip22/ip22-time.c
+++ b/arch/mips/sgi-ip22/ip22-time.c
@@ -35,7 +35,9 @@ static unsigned long indy_rtc_get_time(v
 {
 	unsigned int yrs, mon, day, hrs, min, sec;
 	unsigned int save_control;
+	unsigned long flags;
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	save_control = hpc3c0->rtcregs[RTC_CMD] & 0xff;
 	hpc3c0->rtcregs[RTC_CMD] = save_control | RTC_TE;
 
@@ -47,6 +49,7 @@ static unsigned long indy_rtc_get_time(v
 	yrs = BCD2BIN(hpc3c0->rtcregs[RTC_YEAR] & 0xff);
 
 	hpc3c0->rtcregs[RTC_CMD] = save_control;
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	if (yrs < 45)
 		yrs += 30;
@@ -60,6 +63,7 @@ static int indy_rtc_set_time(unsigned lo
 {
 	struct rtc_time tm;
 	unsigned int save_control;
+	unsigned long flags;
 
 	to_tm(tim, &tm);
 
@@ -68,6 +72,7 @@ static int indy_rtc_set_time(unsigned lo
 	if (tm.tm_year >= 100)
 		tm.tm_year -= 100;
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	save_control = hpc3c0->rtcregs[RTC_CMD] & 0xff;
 	hpc3c0->rtcregs[RTC_CMD] = save_control | RTC_TE;
 
@@ -80,6 +85,7 @@ static int indy_rtc_set_time(unsigned lo
 	hpc3c0->rtcregs[RTC_HUNDREDTH_SECOND] = 0;
 
 	hpc3c0->rtcregs[RTC_CMD] = save_control;
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	return 0;
 }
diff --git a/arch/mips/sibyte/swarm/rtc_m41t81.c b/arch/mips/sibyte/swarm/rtc_m41t81.c
--- a/arch/mips/sibyte/swarm/rtc_m41t81.c
+++ b/arch/mips/sibyte/swarm/rtc_m41t81.c
@@ -144,6 +144,7 @@ static int m41t81_write(uint8_t addr, in
 int m41t81_set_time(unsigned long t)
 {
 	struct rtc_time tm;
+	unsigned long flags;
 
 	to_tm(t, &tm);
 
@@ -153,6 +154,7 @@ int m41t81_set_time(unsigned long t)
 	 * believe we should finish writing min within a second.
 	 */
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	tm.tm_sec = BIN2BCD(tm.tm_sec);
 	m41t81_write(M41T81REG_SC, tm.tm_sec);
 
@@ -180,6 +182,7 @@ int m41t81_set_time(unsigned long t)
 	tm.tm_year %= 100;
 	tm.tm_year = BIN2BCD(tm.tm_year);
 	m41t81_write(M41T81REG_YR, tm.tm_year);
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	return 0;
 }
@@ -187,19 +190,23 @@ int m41t81_set_time(unsigned long t)
 unsigned long m41t81_get_time(void)
 {
 	unsigned int year, mon, day, hour, min, sec;
+	unsigned long flags;
 
 	/*
 	 * min is valid if two reads of sec are the same.
 	 */
 	for (;;) {
+		spin_lock_irqsave(&rtc_lock, flags);
 		sec = m41t81_read(M41T81REG_SC);
 		min = m41t81_read(M41T81REG_MN);
 		if (sec == m41t81_read(M41T81REG_SC)) break;
+		spin_unlock_irqrestore(&rtc_lock, flags);
 	}
 	hour = m41t81_read(M41T81REG_HR) & 0x3f;
 	day = m41t81_read(M41T81REG_DT);
 	mon = m41t81_read(M41T81REG_MO);
 	year = m41t81_read(M41T81REG_YR);
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	sec = BCD2BIN(sec);
 	min = BCD2BIN(min);
diff --git a/arch/mips/sibyte/swarm/rtc_xicor1241.c b/arch/mips/sibyte/swarm/rtc_xicor1241.c
--- a/arch/mips/sibyte/swarm/rtc_xicor1241.c
+++ b/arch/mips/sibyte/swarm/rtc_xicor1241.c
@@ -113,9 +113,11 @@ int xicor_set_time(unsigned long t)
 {
 	struct rtc_time tm;
 	int tmp;
+	unsigned long flags;
 
 	to_tm(t, &tm);
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	/* unlock writes to the CCR */
 	xicor_write(X1241REG_SR, X1241REG_SR_WEL);
 	xicor_write(X1241REG_SR, X1241REG_SR_WEL | X1241REG_SR_RWEL);
@@ -160,6 +162,7 @@ int xicor_set_time(unsigned long t)
 	xicor_write(X1241REG_HR, tmp);
 
 	xicor_write(X1241REG_SR, 0);
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	return 0;
 }
@@ -167,7 +170,9 @@ int xicor_set_time(unsigned long t)
 unsigned long xicor_get_time(void)
 {
 	unsigned int year, mon, day, hour, min, sec, y2k;
+	unsigned long flags;
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	sec = xicor_read(X1241REG_SC);
 	min = xicor_read(X1241REG_MN);
 	hour = xicor_read(X1241REG_HR);
@@ -183,6 +188,7 @@ unsigned long xicor_get_time(void)
 	mon = xicor_read(X1241REG_MO);
 	year = xicor_read(X1241REG_YR);
 	y2k = xicor_read(X1241REG_Y2K);
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	sec = BCD2BIN(sec);
 	min = BCD2BIN(min);
diff --git a/include/asm-mips/mc146818-time.h b/include/asm-mips/mc146818-time.h
--- a/include/asm-mips/mc146818-time.h
+++ b/include/asm-mips/mc146818-time.h
@@ -33,7 +33,9 @@ static inline int mc146818_set_rtc_mmss(
 	int real_seconds, real_minutes, cmos_minutes;
 	unsigned char save_control, save_freq_select;
 	int retval = 0;
+	unsigned long flags;
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	save_control = CMOS_READ(RTC_CONTROL); /* tell the clock it's being set */
 	CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
 
@@ -79,14 +81,30 @@ static inline int mc146818_set_rtc_mmss(
 	 */
 	CMOS_WRITE(save_control, RTC_CONTROL);
 	CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	return retval;
 }
 
+/*
+ * Returns true if a clock update is in progress
+ */
+static inline unsigned char rtc_is_updating(void)
+{
+	unsigned char uip;
+	unsigned long flags;
+
+	spin_lock_irqsave(&rtc_lock, flags);
+	uip = (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP);
+	spin_unlock_irqrestore(&rtc_lock, flags);
+	return uip;
+}
+
 static inline unsigned long mc146818_get_cmos_time(void)
 {
 	unsigned int year, mon, day, hour, min, sec;
 	int i;
+	unsigned long flags;
 
 	/*
 	 * The Linux interpretation of the CMOS clock register contents:
@@ -97,12 +115,13 @@ static inline unsigned long mc146818_get
 
 	/* read RTC exactly on falling edge of update flag */
 	for (i = 0 ; i < 1000000 ; i++)	/* may take up to 1 second... */
-		if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP)
+		if (rtc_is_updating())
 			break;
 	for (i = 0 ; i < 1000000 ; i++)	/* must try at least 2.228 ms */
-		if (!(CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP))
+		if (!rtc_is_updating())
 			break;
 
+	spin_lock_irqsave(&rtc_lock, flags);
 	do { /* Isn't this overkill ? UIP above should guarantee consistency */
 		sec = CMOS_READ(RTC_SECONDS);
 		min = CMOS_READ(RTC_MINUTES);
@@ -120,6 +139,7 @@ static inline unsigned long mc146818_get
 		BCD_TO_BIN(mon);
 		BCD_TO_BIN(year);
 	}
+	spin_unlock_irqrestore(&rtc_lock, flags);
 	year = mc146818_decode_year(year);
 
 	return mktime(year, mon, day, hour, min, sec);
diff --git a/include/asm-mips/time.h b/include/asm-mips/time.h
--- a/include/asm-mips/time.h
+++ b/include/asm-mips/time.h
@@ -20,6 +20,9 @@
 #include <linux/linkage.h>
 #include <linux/ptrace.h>
 #include <linux/rtc.h>
+#include <linux/spinlock.h>
+
+extern spinlock_t rtc_lock;
 
 /*
  * RTC ops.  By default, they point to no-RTC functions.

Re: [PATCH] use rtc_lock to protect RTC operations

[Ralf Baechle]

On Thu, Nov 03, 2005 at 01:01:15AM +0900, Atsushi Nemoto wrote:

> Many RTC routines are not protected each other.  There are potential
> race, for example, ntp-update and /dev/rtc.  This patch fixes them
> using rtc_lock.
> 
> Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>

> --- a/arch/mips/dec/time.c
> +++ b/arch/mips/dec/time.c
> @@ -37,10 +37,25 @@
>  #include <asm/dec/machtype.h>
>  
>  
> +/*
> + * Returns true if a clock update is in progress
> + */
> +static inline unsigned char dec_rtc_is_updating(void)
> +{
> +	unsigned char uip;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&rtc_lock, flags);
> +	uip = (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP);
> +	spin_unlock_irqrestore(&rtc_lock, flags);

Unlike on PC CMOS_READ on a DEC is a single read operation, so atomic
and so doesn't need to be protected.  I'd have to check the datasheet
for any other reason why it might need locking though, so I apply your
patch for now and leave this to Maciej for later optimization.

  Ralf

Re: [PATCH] use rtc_lock to protect RTC operations

[Maciej W. Rozycki]

On Thu, 3 Nov 2005, Ralf Baechle wrote:

> Unlike on PC CMOS_READ on a DEC is a single read operation, so atomic
> and so doesn't need to be protected.  I'd have to check the datasheet
> for any other reason why it might need locking though, so I apply your
> patch for now and leave this to Maciej for later optimization.

 You are correct -- unless you need to perform multiple RTC access cycles
uninterrupted in a row, a lock is not needed.  Single accesses are
executed as single cycles on the system bus, with some glue logic attached
to the RTC chip converting them into pairs of chip accesses consisting of
an index register write and the actual data cycle.  Even the exact latency
of the whole operation is specified for some system models. ;-)

 Welcome to a clean design!

  Maciej

Re: [PATCH] use rtc_lock to protect RTC operations

[Atsushi Nemoto]

>>>>> On Thu, 3 Nov 2005 13:15:32 +0000 (GMT), "Maciej W. Rozycki" <macro@linux-mips.org> said:

>> Unlike on PC CMOS_READ on a DEC is a single read operation, so
>> atomic and so doesn't need to be protected.  I'd have to check the
>> datasheet for any other reason why it might need locking though, so
>> I apply your patch for now and leave this to Maciej for later
>> optimization.

macro>  You are correct -- unless you need to perform multiple RTC
macro> access cycles uninterrupted in a row, a lock is not needed.

Then the dec_rtc_is_updating would be one liner:

	return (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP);

What good hardware!

---
Atsushi Nemoto