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| author | Jagadeesh Pagadala <jpagadal@qti.qualcomm.com> | 2026-07-02 19:39:02 +0530 |
|---|---|---|
| committer | Marek Szyprowski <m.szyprowski@samsung.com> | 2026-07-17 09:15:38 +0200 |
| commit | 3cf67bbc5e5323b3af968bb289cdff33f6180535 (patch) | |
| tree | 1fd9515161939a36e61236ad29b8e14f5401c992 /Documentation/core-api | |
| parent | 0188616c057d3eba8d8a4af62a59b5e7f2362571 (diff) | |
| download | linux-next-3cf67bbc5e5323b3af968bb289cdff33f6180535.tar.gz linux-next-3cf67bbc5e5323b3af968bb289cdff33f6180535.zip | |
dma/swiotlb: introduce Kconfig option for compile-time default pool size
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>
Diffstat (limited to 'Documentation/core-api')
| -rw-r--r-- | Documentation/core-api/swiotlb.rst | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/Documentation/core-api/swiotlb.rst b/Documentation/core-api/swiotlb.rst index 9e0fe027dd3b..71b4e4c27eb5 100644 --- a/Documentation/core-api/swiotlb.rst +++ b/Documentation/core-api/swiotlb.rst @@ -140,8 +140,11 @@ Data structures concepts ------------------------ Memory used for swiotlb bounce buffers is allocated from overall system memory as one or more "pools". The default pool is allocated during system boot with a -default size of 64 MiB. The default pool size may be modified with the -"swiotlb=" kernel boot line parameter. The default size may also be adjusted +default size of 64 MiB, which can be changed at compile time via +CONFIG_SWIOTLB_DEFAULT_SIZE_MB. The default pool size may also be +modified at runtime with the "swiotlb=" kernel boot line parameter, +which takes precedence over the compile-time default. The default size +may also be adjusted due to other conditions, such as running in a CoCo VM, as described above. If CONFIG_SWIOTLB_DYNAMIC is enabled, additional pools may be allocated later in the life of the system. Each pool must be a contiguous range of physical |