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swiotlb: Add swiotlb=noforce debug option 

On architectures like arm64, swiotlb is tied intimately to the core
architecture DMA support. In addition, ZONE_DMA cannot be disabled.

To aid debugging and catch devices not supporting DMA to memory outside
the 32-bit address space, add a kernel command line option
"swiotlb=noforce", which disables the use of bounce buffers.
If specified, trying to map memory that cannot be used with DMA will
fail, and a rate-limited warning will be printed.

Note that io_tlb_nslabs is set to 1, which is the minimal supported
value.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
This commit is contained in:
Geert Uytterhoeven 2016-12-16 14:28:42 +01:00 committed by Konrad Rzeszutek Wilk
parent ae7871be18
commit fff5d99225
4 changed files with 21 additions and 4 deletions
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3
Documentation/admin-guide/kernel-parameters.txt
View File

@ -3807,10 +3807,11 @@
it if 0 is given (See Documentation/cgroup-v1/memory.txt)
swiotlb= [ARM,IA-64,PPC,MIPS,X86]
Format: { <int> | force }
Format: { <int> | force | noforce }
<int> -- Number of I/O TLB slabs
force -- force using of bounce buffers even if they
wouldn't be automatically used by the kernel
noforce -- Never use bounce buffers (for debugging)
switches= [HW,M68k]

1
include/linux/swiotlb.h
View File

@ -12,6 +12,7 @@ struct scatterlist;
enum swiotlb_force {
SWIOTLB_NORMAL, /* Default - depending on HW DMA mask etc. */
SWIOTLB_FORCE, /* swiotlb=force */
SWIOTLB_NO_FORCE, /* swiotlb=noforce */
};
extern enum swiotlb_force swiotlb_force;

3
include/trace/events/swiotlb.h
View File

@ -39,7 +39,8 @@ TRACE_EVENT(swiotlb_bounced,
__entry->size,
__print_symbolic(__entry->swiotlb_force,
{ SWIOTLB_NORMAL, "NORMAL" },
{ SWIOTLB_FORCE, "FORCE" }))
{ SWIOTLB_FORCE, "FORCE" },
{ SWIOTLB_NO_FORCE, "NO_FORCE" }))
);
#endif /* _TRACE_SWIOTLB_H */

18
lib/swiotlb.c
View File

@ -106,8 +106,12 @@ setup_io_tlb_npages(char *str)
}
if (*str == ',')
++str;
if (!strcmp(str, "force"))
if (!strcmp(str, "force")) {
swiotlb_force = SWIOTLB_FORCE;
} else if (!strcmp(str, "noforce")) {
swiotlb_force = SWIOTLB_NO_FORCE;
io_tlb_nslabs = 1;
}
return 0;
}
@ -543,8 +547,15 @@ static phys_addr_t
map_single(struct device *hwdev, phys_addr_t phys, size_t size,
enum dma_data_direction dir, unsigned long attrs)
{
dma_addr_t start_dma_addr = phys_to_dma(hwdev, io_tlb_start);
dma_addr_t start_dma_addr;
if (swiotlb_force == SWIOTLB_NO_FORCE) {
dev_warn_ratelimited(hwdev, "Cannot do DMA to address %pa\n",
&phys);
return SWIOTLB_MAP_ERROR;
}
start_dma_addr = phys_to_dma(hwdev, io_tlb_start);
return swiotlb_tbl_map_single(hwdev, start_dma_addr, phys, size,
dir, attrs);
}
@ -721,6 +732,9 @@ static void
swiotlb_full(struct device *dev, size_t size, enum dma_data_direction dir,
int do_panic)
{
if (swiotlb_force == SWIOTLB_NO_FORCE)
return;
/*
* Ran out of IOMMU space for this operation. This is very bad.
* Unfortunately the drivers cannot handle this operation properly.