iommu: Indicate queued flushes via gather data

mainline inclusion
from mainline-v5.15-rc1
commit 7a7c5bad
category: bugfix
bugzilla: https://gitee.com/openeuler/intel-kernel/issues/I8C8B4
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7a7c5badf85806eab75e31ab8d45021f1545b0e3



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Intel-SIG: commit 7a7c5bad iommu: Indicate queued flushes via gather data
Backport SPR and EMR IOMMU PCIe related upstream bugfixes to kernel 5.10.

Since iommu_iotlb_gather exists to help drivers optimise flushing for a
given unmap request, it is also the logical place to indicate whether
the unmap is strict or not, and thus help them further optimise for
whether to expect a sync or a flush_all subsequently. As part of that,
it also seems fair to make the flush queue code take responsibility for
enforcing the really subtle ordering requirement it brings, so that we
don't need to worry about forgetting that if new drivers want to add
flush queue support, and can consolidate the existing versions.

While we're adding to the kerneldoc, also fill in some info for
@freelist which was overlooked previously.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/bf5f8e2ad84e48c712ccbf80fa8c610594c7595f.1628682049.git.robin.murphy@arm.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>
(cherry picked from commit 7a7c5bad)
Signed-off-by: Ethan Zhao <haifeng.zhao@linux.intel.com>