dma/swiotlb: introduce Kconfig option for compile-time default pool size

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The SWIOTLB bounce buffer pool size is hardcoded at 64 MB via
IO_TLB_DEFAULT_SIZE with no compile-time knob to adjust it. On
memory-constrained embedded or mobile platforms equipped with a
hardware IOMMU (e.g., ARM SMMU) covering most DMA-capable devices,
reserving 64 MB at boot is unnecessarily wasteful — the SWIOTLB is
only exercised for devices that bypass the IOMMU or have restricted
DMA address ranges.

Introduce CONFIG_SWIOTLB_DEFAULT_SIZE_MB, an integer Kconfig option
(range 1–64 MB, default 64) that allows platforms to set a smaller
compile-time default. IO_TLB_DEFAULT_SIZE is updated to derive from
this value when CONFIG_SWIOTLB is enabled, preserving the existing
64 MB default when the option is not configured.

The runtime "swiotlb=<nslabs>" kernel parameter override remains
fully supported and takes precedence over the compile-time default.

Signed-off-by: Jagadeesh Pagadala <jpagadal@qti.qualcomm.com>
Signed-off-by: Bibek Kumar Patro <bibek.patro@oss.qualcomm.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Link: https://lore.kernel.org/r/20260702-swiotlb-v2-1-9205f3ba5408@oss.qualcomm.com
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

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Jagadeesh Pagadala 2026-07-02 19:39:02 +05:30 • committed by Marek Szyprowski

parent 0188616c05

commit 3cf67bbc5e

3 changed files with 33 additions and 4 deletions

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7

Documentation/core-api/swiotlb.rst

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8

include/linux/swiotlb.h

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22

kernel/dma/Kconfig

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