RISC-V: Support non-coherent DMA operations

** Do not upstream **

This is hacky fix just for testing. The actual patch would read the
RISCV_UNCACHED_OFFSET from the DT for only the non-coherent devices.
All other devices on beagleV and all other platform should just set
dma_default_coherent to true.

[Emil: remove spurious whitespace and fix format string warning]

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>

arch/riscv/Kconfig

@@ -208,6 +208,20 @@ config PGTABLE_LEVELS
 config LOCKDEP_SUPPORT
 	def_bool y
 
+config RISCV_UNCACHED_OFFSET
+	hex "Base address of uncached alias"
+	default 0xF80000000 if ARCH_HAS_DMA_SET_UNCACHED && SOC_STARFIVE
+	default 0 if !ARCH_HAS_DMA_SET_UNCACHED
+
+config RISCV_DMA_NONCOHERENT
+	bool
+	select ARCH_HAS_DMA_PREP_COHERENT
+	select ARCH_HAS_SYNC_DMA_FOR_DEVICE
+	select ARCH_HAS_SYNC_DMA_FOR_CPU
+	select ARCH_HAS_DMA_SET_UNCACHED
+	select ARCH_HAS_DMA_CLEAR_UNCACHED
+	select ARCH_HAS_SETUP_DMA_OPS
+
 source "arch/riscv/Kconfig.socs"
 source "arch/riscv/Kconfig.erratas"
 

arch/riscv/Kconfig.socs

@@ -23,6 +23,7 @@ config SOC_STARFIVE
 	bool "StarFive SoCs"
 	select PINCTRL
 	select RESET_CONTROLLER
+	select RISCV_DMA_NONCOHERENT
 	select SIFIVE_L2
 	select SIFIVE_L2_FLUSH
 	select SIFIVE_PLIC

arch/riscv/mm/Makefile

@@ -30,3 +30,4 @@ endif
 endif
 
 obj-$(CONFIG_DEBUG_VIRTUAL) += physaddr.o
+obj-$(CONFIG_RISCV_DMA_NONCOHERENT) += dma-noncoherent.o

arch/riscv/mm/dma-noncoherent.c

@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * DMA mapping implementation inspired from arm/mm/dma-mapping.c
+ *
+ * Copyright (c) 2021 Western Digital Corporation or its affiliates.
+ */
+
+#include <linux/dma-direct.h>
+#include <linux/dma-map-ops.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/mm.h>
+#include <asm/cpu_ops.h>
+#include <asm/sbi.h>
+#include <asm/smp.h>
+
+//TODO Do it through SBI
+#include <soc/sifive/sifive_l2_cache.h>
+
+void arch_sync_dma_for_device(phys_addr_t paddr, size_t size, enum dma_data_direction dir)
+{
+	sifive_l2_flush64_range(paddr, size);
+}
+
+void arch_sync_dma_for_cpu(phys_addr_t paddr, size_t size, enum dma_data_direction dir)
+{
+	sifive_l2_flush64_range(paddr, size);
+}
+
+void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
+		const struct iommu_ops *iommu, bool coherent)
+{
+	dev_info(dev, "coherent device %d dev->dma_coherent %d\n", coherent, dev->dma_coherent);
+	dev->dma_coherent = coherent;
+}
+
+//TODO: We are supposed to invalidate the cache here
+void arch_dma_prep_coherent(struct page *page, size_t size)
+{
+	void *flush_addr = page_address(page);
+
+	memset(flush_addr, 0, size);
+	sifive_l2_flush64_range(__pa(flush_addr), size);
+}
+
+void arch_dma_clear_uncached(void *addr, size_t size)
+{
+	memunmap(addr);
+}
+
+void *arch_dma_set_uncached(void *addr, size_t size)
+{
+	phys_addr_t phys_addr = __pa(addr) + CONFIG_RISCV_UNCACHED_OFFSET;
+	void *mem_base = NULL;
+
+	mem_base = memremap(phys_addr, size, MEMREMAP_WT);
+	if (!mem_base) {
+		pr_err("%s memremap failed for addr %px\n", __func__, addr);
+		return ERR_PTR(-EINVAL);
+	}
+
+	return mem_base;
+}