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=nobounce", which disables the use of bounce buffers.
If specified, trying to map memory that cannot be used with DMA will
fail, and a warning will be printed (rate-limited).
Note that io_tlb_nslabs is set to 1, which is the minimal supported
value.
Signed-off-by: Geert Uytterhoeven <geert+rene...@glider.be>
---
Documentation/kernel-parameters.txt | 3 ++-
lib/swiotlb.c | 19 +++++++++++++++++--
2 files changed, 19 insertions(+), 3 deletions(-)
diff --git a/Documentation/kernel-parameters.txt
b/Documentation/kernel-parameters.txt
index 37babf91f2cb6de2..38556cdceabaf087 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3998,10 +3998,11 @@ bytes respectively. Such letter suffixes can also be
entirely omitted.
it if 0 is given (See
Documentation/cgroup-v1/memory.txt)
swiotlb= [ARM,IA-64,PPC,MIPS,X86]
- Format: { <int> | force }
+ Format: { <int> | force | nobounce }
<int> -- Number of I/O TLB slabs
force -- force using of bounce buffers even if they
wouldn't be automatically used by the kernel
+ nobounce -- Never use bounce buffers (for debugging)
switches= [HW,M68k]
diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index 6ce764410ae475cc..4550e6b516c2a4c0 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -54,6 +54,7 @@
#define IO_TLB_MIN_SLABS ((1<<20) >> IO_TLB_SHIFT)
int swiotlb_force;
+static int swiotlb_nobounce;
/*
* Used to do a quick range check in swiotlb_tbl_unmap_single and
@@ -106,8 +107,12 @@
}
if (*str == ',')
++str;
- if (!strcmp(str, "force"))
+ if (!strcmp(str, "force")) {
swiotlb_force = 1;
+ } else if (!strcmp(str, "nobounce")) {
+ swiotlb_nobounce = 1;
+ io_tlb_nslabs = 1;
+ }
return 0;
}
@@ -541,8 +546,15 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
map_single(struct device *hwdev, phys_addr_t phys, size_t size,
enum dma_data_direction dir)
{
- dma_addr_t start_dma_addr = phys_to_dma(hwdev, io_tlb_start);
+ dma_addr_t start_dma_addr;
+
+ if (swiotlb_nobounce) {
+ 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);
}
@@ -707,6 +719,9 @@ void swiotlb_tbl_sync_single(struct device *hwdev,
phys_addr_t tlb_addr,
swiotlb_full(struct device *dev, size_t size, enum dma_data_direction dir,
int do_panic)
{
+ if (swiotlb_nobounce)
+ return;
+
/*
* Ran out of IOMMU space for this operation. This is very bad.
* Unfortunately the drivers cannot handle this operation properly.
--
1.9.1
