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Since the meaning of the SR_LBAT85 and SR_LBAT75 bits are different in battery backup mode, they may very well be set after power on, and stay set for up to a minute (i.e. until the battery detection in VDD mode happens when the seconds counter hits 59). This would mean that userspace doing a ioctl(RTC_VL_READ) early on could get a false positive. The battery level detection can also be triggered by explicitly writing a 1 to the TSE bit in the BETA register. Do that once during boot. Empirically, this does not immediately update the bits in the status register (i.e., an immediate read of SR after this write can still show stale values), but the update is done after a few milliseconds, so certainly before the RTC device gets registered and userspace has a chance of doing the ioctl() on this device. Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> Link: https://lore.kernel.org/r/20230615105826.411953-7-linux@rasmusvillemoes.dk Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.