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The GT MCR code currently relies on uncore->lock to avoid race conditions on the steering control register during MCR operations. The *_fw() versions of MCR operations expect the caller to already hold uncore->lock, while the non-fw variants manage the lock internally. However the sole callsite of intel_gt_mcr_wait_for_reg_fw() does not currently obtain the forcewake lock, allowing a potential race condition (and triggering an assertion on lockdep builds). Furthermore, since 'wait for register value' requests may not return immediately, it is undesirable to hold a fundamental lock like uncore->lock for the entire wait and block all other MMIO for the duration; rather the lock is only needed around the MCR read operations and can be released during the delays. Convert intel_gt_mcr_wait_for_reg_fw() to a non-fw variant that will manage uncore->lock internally. This does have the side effect of causing an unnecessary lookup in the forcewake table on each read operation, but since the caller is still holding the relevant forcewake domain, this will ultimately just incremenent the reference count and won't actually cause any additional MMIO traffic. In the future we plan to switch to a dedicated MCR lock to protect the steering critical section rather than using the overloaded and high-traffic uncore->lock; on MTL and beyond the new lock can be implemented on top of the hardware-provided synchonization mechanism for steering. Fixes: |
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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.