From 10314e09d044296bc50dec831aa85b3ae1acedf0 Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@lst.de>
Date: Fri, 27 Apr 2018 08:43:14 +0200
Subject: [PATCH] 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: Christoph Hellwig <hch@lst.de>
Reviewed-by: Palmer Dabbelt <palmer@sifive.com>
---
arch/riscv/Kconfig | 1 +
arch/riscv/include/asm/dma-mapping.h | 15 +++++++++++++++
arch/riscv/kernel/setup.c | 2 ++
3 files changed, 18 insertions(+)
create mode 100644 arch/riscv/include/asm/dma-mapping.h
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index c4488ce8c2fa4..274bc064c41f8 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -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
diff --git a/arch/riscv/include/asm/dma-mapping.h b/arch/riscv/include/asm/dma-mapping.h
new file mode 100644
index 0000000000000..8facc1c8fa054
--- /dev/null
+++ b/arch/riscv/include/asm/dma-mapping.h
@@ -0,0 +1,15 @@
+// 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 */
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index c11f40c1b2a88..ee44a48faf79d 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -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();
--
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