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[ Upstream commit 8876fc1884f5b39550c8387ff3176396c988541d ] Envelope struct is always initialized, but the envelope itself is optional as described in USB PID Device class definition 1.0. 5.1.1.1 Type Specific Block Offsets ... 4) Effects that do not use Condition Blocks use 1 Parameter Block and an *optional* Envelope Block. Sending out "empty" envelope breaks force feedback on some devices with games that use SINE effect + offset to emulate constant force effect, as well as generally breaking Constant/Periodic effects. One of the affected brands is Moza Racing. This change prevents the envelope from being sent if it contains all 0 values while keeping the old behavior of only sending it, if it differs from the old one. Changes in v6: - Simplify the checks to make them clearer - Fix possible null pointer dereference while calling pidff_needs_set_envelope Signed-off-by: Tomasz Pakuła <tomasz.pakula.oficjalny@gmail.com> Reviewed-by: Michał Kopeć <michal@nozomi.space> Reviewed-by: Paul Dino Jones <paul@spacefreak18.xyz> Tested-by: Paul Dino Jones <paul@spacefreak18.xyz> Tested-by: Cristóferson Bueno <cbueno81@gmail.com> Tested-by: Pablo Cisneros <patchkez@protonmail.com> Signed-off-by: Jiri Kosina <jkosina@suse.com> Signed-off-by: Sasha Levin <sashal@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.