diff options
| 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 /kernel | |
| parent | 0188616c057d3eba8d8a4af62a59b5e7f2362571 (diff) | |
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 'kernel')
| -rw-r--r-- | kernel/dma/Kconfig | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig index 0a4ba21a57a7..3830a63ae032 100644 --- a/kernel/dma/Kconfig +++ b/kernel/dma/Kconfig @@ -86,6 +86,28 @@ config SWIOTLB bool select NEED_DMA_MAP_STATE +config SWIOTLB_DEFAULT_SIZE_MB + int "Default SWIOTLB bounce buffer size in MB" + depends on SWIOTLB + range 1 64 + default 64 + help + Sets the default size of the software IO TLB (SWIOTLB) bounce buffer + pool allocated at boot time. The default is 64 MB. + + On memory-constrained embedded or mobile platforms (e.g., those with + a hardware IOMMU such as ARM SMMU covering most DMA-capable devices), + a smaller value such as 4 or 8 MB may be sufficient. The SWIOTLB is + then only needed for devices that bypass the IOMMU or have restricted + DMA address ranges. + + The minimum allowed value is 1 MB. This compile-time default can be + overridden at runtime using the "swiotlb=<nslabs>" kernel command line + parameter. Refer to Documentation/admin-guide/kernel-parameters.txt + for details. + + If unsure, leave at the default value of 64. + config SWIOTLB_DYNAMIC bool "Dynamic allocation of DMA bounce buffers" default n |