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authorThomas Gleixner <tglx@linutronix.de>2021-01-26 20:02:11 +0300
committerThomas Gleixner <tglx@linutronix.de>2021-01-27 11:36:22 +0300
commit211e5db19d15a721b2953ea54b8f26c2963720eb (patch)
treeb8347d98437f5ac8527f9c36e1620635c50a5501 /drivers/rtc/rtc-mc146818-lib.c
parent13391c60da3308ed9980de0168f74cce6c62ac1d (diff)
downloadlinux-211e5db19d15a721b2953ea54b8f26c2963720eb.tar.xz
rtc: mc146818: Detect and handle broken RTCs
The recent fix for handling the UIP bit unearthed another issue in the RTC code. If the RTC is advertised but the readout is straight 0xFF because it's not available, the old code just proceeded with crappy values, but the new code hangs because it waits for the UIP bit to become low. Add a sanity check in the RTC CMOS probe function which reads the RTC_VALID register (Register D) which should have bit 0-6 cleared. If that's not the case then fail to register the CMOS. Add the same check to mc146818_get_time(), warn once when the condition is true and invalidate the rtc_time data. Reported-by: Mickaël Salaün <mic@digikod.net> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Mickaël Salaün <mic@linux.microsoft.com> Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com> Link: https://lore.kernel.org/r/87tur3fx7w.fsf@nanos.tec.linutronix.de
Diffstat (limited to 'drivers/rtc/rtc-mc146818-lib.c')
-rw-r--r--drivers/rtc/rtc-mc146818-lib.c7
1 files changed, 7 insertions, 0 deletions
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