[Bug 211713] NVME controller failure: resetting (Samsung SM961 SSD Drives)

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=211713

--- Comment #78 from Ka Ho Ng <khng300 at gmail.com> ---
(In reply to Warner Losh from comment #77)

The commit message of the patch is actually inside this commit:
https://github.com/khng300/freebsd/commit/c75f08495fde5dee08e4b24f399f2d70a77254a6

To put simply, some controllers give zeroes for MMIO read on certain regions,
and subsequently leading to MSI-X not being enabled at all (the interrupts will
first be masked and it will be in effect, however the subsequent unmask will
not work at all). As a result the corresponding bit in PBA will be set by the
controller since the interrupt is actually not enabled after being masked
(recall that the read of vector control word will always give zero). Such
modification is actually made by taking a reference at the interrupt unmask
implementation of Illumos kernel, by not considering the existing content of
vector control bit but simply overwriting the word.

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