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dma: swiotlb: introduce CONFIG_SWIOTLB_DEFAULT_SIZE_MB Kconfig #707

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dma: swiotlb: introduce CONFIG_SWIOTLB_DEFAULT_SIZE_MB Kconfig #707

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1 change: 1 addition & 0 deletions arch/arm64/configs/qcom.config
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Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,7 @@ CONFIG_STM_PROTO_SYS_T=m
CONFIG_STM_SOURCE_CONSOLE=m
CONFIG_STM_SOURCE_FTRACE=m
CONFIG_STM_SOURCE_HEARTBEAT=m
CONFIG_SWIOTLB_DEFAULT_SIZE_MB=2
CONFIG_SENSORS_AMC6821=y
CONFIG_SENSORS_EMC2305=y
CONFIG_SENSORS_QCOM_BCL=y
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12 changes: 10 additions & 2 deletions include/linux/swiotlb.h
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Expand Up @@ -32,8 +32,16 @@ struct scatterlist;
#define IO_TLB_SHIFT 11
#define IO_TLB_SIZE (1 << IO_TLB_SHIFT)

/* default to 64MB */
#define IO_TLB_DEFAULT_SIZE (64UL<<20)
/*
* Default SWIOTLB bounce buffer pool size.
* Configurable at compile time via CONFIG_SWIOTLB_DEFAULT_SIZE_MB.
* Falls back to 64 MB if not set via Kconfig.
*/
#if defined(CONFIG_SWIOTLB) && defined(CONFIG_SWIOTLB_DEFAULT_SIZE_MB)
#define IO_TLB_DEFAULT_SIZE ((unsigned long)CONFIG_SWIOTLB_DEFAULT_SIZE_MB << 20)
#else
#define IO_TLB_DEFAULT_SIZE (64UL << 20)
#endif

unsigned long swiotlb_size_or_default(void);
void __init swiotlb_init_remap(bool addressing_limit, unsigned int flags,
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21 changes: 21 additions & 0 deletions kernel/dma/Kconfig
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Expand Up @@ -89,6 +89,27 @@ 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, where nslabs = (desired_size_in_bytes / 2048).

If unsure, leave at the default value of 64.

config SWIOTLB_DYNAMIC
bool "Dynamic allocation of DMA bounce buffers"
default n
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