bedb404e91
Doing any kind of power management for kernel console is really bad idea. First of all, it runs in poll and atomic mode. This fact attaches a limitation on the functions that might be called. For example, pm_runtime_get_sync() might sleep and thus can't be used. This call needs, for example, to bring the device to powered on state on the system, where the power on sequence may require on-atomic operations, such as Intel Cherrytrail with ACPI enumerated UARTs. That said, on ACPI enabled platforms it might even call firmware for a job. On the other hand pm_runtime_get() doesn't guarantee that device will become powered on fast enough. Besides that, imagine the case when console is about to print a kernel Oops and it's powered off. In such an emergency case calling the complex functions is not the best what we can do, taking into consideration that user wants to see at least something of the last kernel word before it passes away. Here we modify the 8250 console code to prevent runtime power management. Note, there is a behaviour change for OMAP boards. It will require to detach kernel console to become idle. Link: https://lists.openwall.net/linux-kernel/2018/09/29/65 Suggested-by: Russell King <rmk+kernel@armlinux.org.uk> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Link: https://lore.kernel.org/r/20200217114016.49856-6-andriy.shevchenko@linux.intel.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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.