Linus,
please pull the latest timers/urgent branch from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
timers-urgent-2021-01-31
up to: 211e5db19d15: rtc: mc146818: Detect and handle broken RTCs
A fix for handling advertised, but non-existent 146818 RTCs correctly. With
the recent UIP handling changes the time readout of non-existent RTCs hangs
forever as the read returns always 0xFF which means the UIP bit is
set. Sanity check the RTC before registering by checking the RTC_VALID
register for correctness.
Thanks,
tglx
------------------>
Thomas Gleixner (1):
rtc: mc146818: Detect and handle broken RTCs
drivers/rtc/rtc-cmos.c | 8 ++++++++
drivers/rtc/rtc-mc146818-lib.c | 7 +++++++
2 files changed, 15 insertions(+)
diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index 51e80bc70d42..68a9ac6f2fe1 100644
--- a/drivers/rtc/rtc-cmos.c
+++ b/drivers/rtc/rtc-cmos.c
@@ -805,6 +805,14 @@ cmos_do_probe(struct device *dev, struct resource *ports,
int rtc_irq)
spin_lock_irq(&rtc_lock);
+ /* Ensure that the RTC is accessible. Bit 0-6 must be 0! */
+ if ((CMOS_READ(RTC_VALID) & 0x7f) != 0) {
+ spin_unlock_irq(&rtc_lock);
+ dev_warn(dev, "not accessible\n");
+ retval = -ENXIO;
+ goto cleanup1;
+ }
+
if (!(flags & CMOS_RTC_FLAGS_NOFREQ)) {
/* force periodic irq to CMOS reset default of 1024Hz;
*
diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c
index 972a5b9a629d..f83c13818af3 100644
--- a/drivers/rtc/rtc-mc146818-lib.c
+++ b/drivers/rtc/rtc-mc146818-lib.c
@@ -21,6 +21,13 @@ unsigned int mc146818_get_time(struct rtc_time *time)
again:
spin_lock_irqsave(&rtc_lock, flags);
+ /* Ensure that the RTC is accessible. Bit 0-6 must be 0! */
+ if (WARN_ON_ONCE((CMOS_READ(RTC_VALID) & 0x7f) != 0)) {
+ spin_unlock_irqrestore(&rtc_lock, flags);
+ memset(time, 0xff, sizeof(*time));
+ return 0;
+ }
+
/*
* Check whether there is an update in progress during which the
* readout is unspecified. The maximum update time is ~2ms. Poll
