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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>