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A fix for handling advertised, but non-existent 146818 RTCs correctly. With

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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.
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Merge tag 'timers-urgent-2021-01-31' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull timer fix from Thomas Gleixner:
 "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"

* tag 'timers-urgent-2021-01-31' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  rtc: mc146818: Detect and handle broken RTCs
This commit is contained in:
Linus Torvalds 2021-01-31 11:40:57 -08:00
commit 17b756d037
2 changed files with 15 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
drivers/rtc/rtc-cmos.c
View File

@ -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;
*

7
drivers/rtc/rtc-mc146818-lib.c
View File

@ -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