Linux kernel for uConsole
cd7f3a249d
In order to read correctly from asynchronously updated RTC registers, it's necessary to read repeatedly until their values do not change from read to read. It's also necessary to wait for three RTC clock ticks for certain operations. There are no timeouts in this code and these operations could possibly loop forever. To avoid kernel hangs, put in timeouts. The iMX7d can be configured to stop the SRTC on a tamper event, which will lockup the kernel inside this driver as described above. These hangs can happen when running under qemu, which doesn't emulate the SNVS RTC, though currently the driver will refuse to load on qemu due to a timeout in the driver probe method. It could also happen if the SRTC block where somehow placed into reset or the slow speed clock that drives the SRTC counter (but not the CPU) were to stop. The symptoms on a two core iMX7d are a work queue hang on rtc_timer_do_work(), which eventually blocks a systemd fsnotify operation that triggers a work queue flush, causing systemd to hang and thus causing all services that should be started by systemd, like a console getty, to fail to start or stop. Also optimize the wait code to wait less. It only needs to wait for the clock to advance three ticks, not to see it change three times. Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com> Cc: Alessandro Zummo <a.zummo@towertech.it> Cc: Fabio Estevam <fabio.estevam@nxp.com> Cc: Shawn Guo <shawn.guo@linaro.org> Cc: Bryan O'Donoghue <pure.logic@nexus-software.ie> Signed-off-by: Trent Piepho <tpiepho@impinj.com> Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com> |
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.