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Most H2G messages are FAST_REQ which means no synchronous response is expected. The messages are sent as fire-and-forget with no tracking. However, errors can still be returned when something goes unexpectedly wrong. That leads to confusion due to not being able to match up the error response to the originating H2G. So add support for tracking the FAST_REQ H2Gs and matching up an error response to its originator. This is only enabled in XE_DEBUG builds given that such errors should never happen in a working system and there is an overhead for the tracking. Further, if XE_DEBUG_GUC is enabled then even more memory and time is used to record the call stack of each H2G and report that with the error. That makes it much easier to work out where a specific H2G came from if there are multiple code paths that can send it. v2: Some re-wording of comments and prints, more consistent use of #if vs stub functions - review feedback from Daniele & Michal). v3: Split config change to separate patch, improve a debug print (review feedback from Michal). v4: Bunch of minor tweaks (review feedback from Michal). Original-i915-code: Michal Wajdeczko <michal.wajdeczko@intel.com> Signed-off-by: John Harrison <John.C.Harrison@Intel.com> Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com> Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com> Link: https://lore.kernel.org/r/20250512215324.1457009-5-John.C.Harrison@Intel.com
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 reStructuredText 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.