iommu/arm-smmu-v3: Default queue depths to one page in a kdump kernel

All three queues are sized from the maxima the hardware advertises in IDR1
and allocated at probe, up to 4 MB each on a 4K-page kernel. The capture
kernel already disables two of them: arm_smmu_device_reset() drops
CR0_EVTQEN and CR0_PRIQEN. It still allocates both at full size.

A kdump capture kernel runs from a small crashkernel reservation, and every
SMMUv3 instance pays that cost again, up to 12 MB apiece. It goes to queues
that either serve the handful of devices used to save the dump or are
switched off outright, and it is memory the dump itself needs.

Size all three queues at one page worth of entries when is_kdump_kernel().
The queues carry commands and fault records rather than DMA data, so dump
throughput is unaffected. A shallower command queue only bounds how many
commands may be in flight before a sync, which does not matter for the few
devices that save the dump. The cmdq_max_n_shift parameter therefore does
not apply in a capture kernel.

Suggested-by: Kyle McMartin <jkkm@meta.com>
Assisted-by: LLM
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Tested-by: Yuanhe Shu <xiangzao@linux.alibaba.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Will Deacon <will@kernel.org>

0 files changed, 0 insertions, 0 deletions