Phil Elwell
9fae7f0a49
[ Upstream commit 30ec514d44 ]
The SC16IS752 has an Enhanced Feature Register which is aliased at the
same address as the Interrupt Identification Register; accessing it
requires that a magic value is written to the Line Configuration
Register. If an interrupt is raised while the EFR is mapped in then
the ISR won't be able to access the IIR, leading to the "Unexpected
interrupt" error messages.
Avoid the problem by claiming a mutex around accesses to the EFR
register, also claiming the mutex in the interrupt handler work
item (this is equivalent to disabling interrupts to interlock against
a non-threaded interrupt handler).
See: https://github.com/raspberrypi/linux/issues/2529
Signed-off-by: Phil Elwell <phil@raspberrypi.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. 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.