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Commit fff5d992 authored by Geert Uytterhoeven's avatar Geert Uytterhoeven Committed by Konrad Rzeszutek Wilk
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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: default avatarGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent ae7871be

Documentation/admin-guide/kernel-parameters.txt

+2 −1
Original line number Diff line number Diff line
@@ -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]

include/linux/swiotlb.h

+1 −0
Original line number Diff line number Diff line
@@ -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;

include/trace/events/swiotlb.h

+2 −1
Original line number Diff line number Diff line
@@ -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 */

lib/swiotlb.c

+16 −2
Original line number Diff line number Diff line
@@ -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.