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Commit 10314e09 authored by Christoph Hellwig's avatar Christoph Hellwig
Browse files

riscv: add swiotlb support 



All RISC-V platforms today lack an IOMMU. However, legacy PCI devices
sometimes require DMA-memory to be in the low 32 bits.  To make this work,
we enable the software-based bounce buffers from swiotlb.  They only impose
overhead when the device in question cannot address the full 64-bit address
space, so a perfect fit.

This patch assumes that DMA is coherent with the processor and the PCI
bus.  It also assumes that the processor and devices share a common
address space. This is true for all RISC-V platforms so far.

[changelog stolen from an earlier patch by Palmer Dabbelt that did the
 more complicated swiotlb wireup before the recent consolidation]

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarPalmer Dabbelt <palmer@sifive.com>
parent f1306f04

arch/riscv/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -114,6 +114,7 @@ config ARCH_RV64I 
	select HAVE_FTRACE_MCOUNT_RECORD

	select HAVE_DYNAMIC_FTRACE

	select HAVE_DYNAMIC_FTRACE_WITH_REGS

	select SWIOTLB



endchoice

arch/riscv/include/asm/dma-mapping.h

0 → 100644
+15 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

#ifndef _RISCV_ASM_DMA_MAPPING_H

#define _RISCV_ASM_DMA_MAPPING_H 1



#ifdef CONFIG_SWIOTLB

#include <linux/swiotlb.h>

static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type *bus)

{

	return &swiotlb_dma_ops;

}

#else

#include <asm-generic/dma-mapping.h>

#endif /* CONFIG_SWIOTLB */



#endif /* _RISCV_ASM_DMA_MAPPING_H */

arch/riscv/kernel/setup.c

+2 −0
Original line number Diff line number Diff line
@@ -29,6 +29,7 @@ 
#include <linux/of_fdt.h>

#include <linux/of_platform.h>

#include <linux/sched/task.h>

#include <linux/swiotlb.h>



#include <asm/setup.h>

#include <asm/sections.h>
@@ -206,6 +207,7 @@ void __init setup_arch(char **cmdline_p) 
	setup_bootmem();

	paging_init();

	unflatten_device_tree();

	swiotlb_init(1);



#ifdef CONFIG_SMP

	setup_smp();