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[ Upstream commit 67ea0b7ce41844eae7c10bb04dfe66a23318c224 ] When an overflow occurs in the PRI queue, the SMMU toggles the overflow flag in the PROD register. To exit the overflow condition, the PRI thread is supposed to acknowledge it by toggling this flag in the CONS register. Unacknowledged overflow causes the queue to stop adding anything new. Currently, the priq thread always writes the CONS register back to the SMMU after clearing the queue. The writeback is not necessary if the OVFLG in the PROD register has not been changed, no overflow has occured. This commit checks the difference of the overflow flag between CONS and PROD register. If it's different, toggles the OVACKFLG flag in the CONS register and write it to the SMMU. The situation is similar for the event queue. The acknowledge register is also toggled after clearing the event queue but never propagated to the hardware. This would only be done the next time when executing evtq thread. Unacknowledged event queue overflow doesn't affect the event queue, because the SMMU still adds elements to that queue when the overflow condition is active. But it feel nicer to keep SMMU in sync when possible, so use the same way here as well. Signed-off-by: Tomas Krcka <krckatom@amazon.de> Link: https://lore.kernel.org/r/20230329123420.34641-1-tomas.krcka@gmail.com Signed-off-by: Will Deacon <will@kernel.org> 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.