[PATCH v5 0/2] iommu/arm-smmu-v3: Make the queue depths tunable, and shrink them in a kdump kernel

["Kiryl Shutsemau (Meta)" <kas@kernel.org>]

The queues are sized from the IDR1 maxima and allocated at probe, costing
megabytes per queue per SMMU instance. A kdump capture kernel pays that out
of a small crashkernel reservation, for queues it barely uses and two of
which it switches off anyway.

Patch 1 adds a cmdq_max_entries module parameter, decided in a per-queue
helper and floored at one page. Patch 2 has a kdump kernel default all
three depths to one page through the same helper. An explicit
cmdq_max_entries still wins.

Measured per instance under QEMU on -M virt,iommu=smmuv3, through a real
panic and kexec into a capture kernel:

                        4K page          64K page
      cmdq         1 MB -> 4 KB      8 MB -> 64 KB
      evtq         1 MB -> 4 KB     16 MB -> 64 KB

Every clamped queue lands on exactly one page. cmdq_max_entries moves the
command queue alone and beats the kdump default; the capture kernel
attached four devices with no CMD_SYNC timeout, GERROR or context fault.
QEMU exposes no PRI queue, which takes the same path. Build-tested across
4K/16K/64K, TEGRA241_CMDQV=n, CRASH_DUMP=n and =m, every commit
warning-free.

v5:
 - Rename cmdq_entries to cmdq_max_entries (Nicolin).
 - Take Nicolin's refactor: ceiling/floor naming, the alignment cap inside
   the per-queue helpers, evtq/priq helpers, FIELD_GET() at the call sites.
 - Keep the override in entries rather than a shift: ilog2(1) is 0 and
   collides with the "use the default" sentinel, so cmdq_max_entries=1
   would have given the hardware maximum instead of the floor.
 - min() for min_t() now that the types allow it. Changelogs tightened.

v4: https://lore.kernel.org/all/20260902121724.3494954-1-kas@kernel.org/
v3: https://lore.kernel.org/all/20260706084708.8072-1-kas@kernel.org/

Kiryl Shutsemau (Meta) (2):
  iommu/arm-smmu-v3: Add a cmdq_max_entries module parameter
  iommu/arm-smmu-v3: Default queue depths to one page in a kdump kernel

 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c   | 78 +++++++++++++++++--
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h   |  1 +
 .../iommu/arm/arm-smmu-v3/tegra241-cmdqv.c    |  2 +-
 3 files changed, 73 insertions(+), 8 deletions(-)


base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
-- 
2.54.0