e704b44b55
Drivers for devices with multiple frontends which cannot be used concurrently due to hardware limitations which enforce that restriction by setting the mfe_shared field to 1 exhibit rather unfriendly behavior towards applications: The unavailable frontend devices cannot be opened at all, not even for read-only access to query information. Even worse, any open call is blocked for 5 seconds by default. Allow drivers for such devices to behave like regular busy frontend devices instead, i.e. still allowing concurrent read access to the unavailable frontend and denying concurrent write access with -EBUSY without delay. This patch does not alter the behavior of any existing driver to avoid regressions. Driver developers who wish to take advantage of this must ensure their driver can handle all read-only accesses to the unavailable frontend, and indicate the capability by setting the mfe_shared field to 2 instead of 1. Add a check to dvb-usb-init.c when automatically setting the mfe_shared field that when a driver has already set the field to 2, it is not overwritten. Document the additional capability in the code comment about mfe_shared. Link: https://lore.kernel.org/linux-media/trinity-22c77578-26b0-4867-9ff7-2668e5d22c64-1642799929896@3c-app-gmx-bap04 Signed-off-by: Robert Schlabbach <robert_s@gmx.net> Tested-by: Robert Schlabbach <robert_s@gmx.net> Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.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.