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.
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
2 files changed
