[PATCH RFC 3/3] riscv: Add SYNC_DMA_FOR_CPU/DEVICE for DMA_COHERENT

[guoren@kernel.org]

From: Guo Ren <guoren@linux.alibaba.com>

To support DMA device in a non-coherent interconnect SOC system,
we need the below facilities:
 - Change a memory region attributes from cacheable to strong.
   It would be used in DMA descriptors.
 - Sync the cache with memory before DMA start and after DMA end.
   It would be used for DMA data transfer buffers.

This patch enables kernel dma/direct.c coherent infrastructure and
a new sbi_ecall API for dma_sync.

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Cc: Anup Patel <anup.patel@wdc.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Drew Fustini <drew@beagleboard.org>
Cc: Palmer Dabbelt <palmerdabbelt@google.com>
Cc: Wei Fu <wefu@redhat.com>
Cc: Wei Wu <lazyparser@gmail.com>
---
 arch/riscv/Kconfig               |  4 ++++
 arch/riscv/include/asm/pgtable.h | 13 +++++++++++++
 arch/riscv/include/asm/sbi.h     | 16 ++++++++++++++++
 arch/riscv/kernel/sbi.c          | 19 +++++++++++++++++++
 arch/riscv/mm/Makefile           |  4 ++++
 arch/riscv/mm/dma-mapping.c      | 41 ++++++++++++++++++++++++++++++++++++++++
 6 files changed, 97 insertions(+)
 create mode 100644 arch/riscv/mm/dma-mapping.c

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 632fac5..94a736a 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -20,6 +20,9 @@ config RISCV
 	select ARCH_HAS_DEBUG_VM_PGTABLE
 	select ARCH_HAS_DEBUG_VIRTUAL if MMU
 	select ARCH_HAS_DEBUG_WX
+	select ARCH_HAS_DMA_PREP_COHERENT if RISCV_DMA_COHERENT
+	select ARCH_HAS_SYNC_DMA_FOR_CPU if RISCV_DMA_COHERENT
+	select ARCH_HAS_SYNC_DMA_FOR_DEVICE if RISCV_DMA_COHERENT
 	select ARCH_HAS_FORTIFY_SOURCE
 	select ARCH_HAS_GCOV_PROFILE_ALL
 	select ARCH_HAS_GIGANTIC_PAGE
@@ -41,6 +44,7 @@ config RISCV
 	select CLONE_BACKWARDS
 	select CLINT_TIMER if !MMU
 	select COMMON_CLK
+	select DMA_DIRECT_REMAP if RISCV_DMA_COHERENT
 	select EDAC_SUPPORT
 	select GENERIC_ARCH_TOPOLOGY if SMP
 	select GENERIC_ATOMIC64 if !64BIT
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index f822f22..8994d58 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -465,6 +465,19 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
 	return ptep_test_and_clear_young(vma, address, ptep);
 }
 
+#ifdef CONFIG_RISCV_DMA_COHERENT
+#define pgprot_noncached pgprot_noncached
+static inline pgprot_t pgprot_noncached(pgprot_t _prot)
+{
+	unsigned long prot = pgprot_val(_prot);
+
+	prot &= ~_PAGE_DMA_MASK;
+	prot |= _PAGE_DMA_NONCACHE;
+
+	return __pgprot(prot);
+}
+#endif
+
 /*
  * Encode and decode a swap entry
  *
diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
index 0d42693..08b4244 100644
--- a/arch/riscv/include/asm/sbi.h
+++ b/arch/riscv/include/asm/sbi.h
@@ -27,6 +27,7 @@ enum sbi_ext_id {
 	SBI_EXT_IPI = 0x735049,
 	SBI_EXT_RFENCE = 0x52464E43,
 	SBI_EXT_HSM = 0x48534D,
+	SBI_EXT_DMA = 0xAB150401,
 };
 
 enum sbi_ext_base_fid {
@@ -37,6 +38,7 @@ enum sbi_ext_base_fid {
 	SBI_EXT_BASE_GET_MVENDORID,
 	SBI_EXT_BASE_GET_MARCHID,
 	SBI_EXT_BASE_GET_MIMPID,
+	SBI_EXT_RFENCE_REMOTE_DMA_SYNC,
 };
 
 enum sbi_ext_time_fid {
@@ -63,6 +65,17 @@ enum sbi_ext_hsm_fid {
 	SBI_EXT_HSM_HART_STATUS,
 };
 
+enum sbi_ext_dma_fid {
+	SBI_DMA_SYNC = 0,
+};
+
+enum sbi_dma_sync_data_direction {
+	SBI_DMA_BIDIRECTIONAL = 0,
+	SBI_DMA_TO_DEVICE = 1,
+	SBI_DMA_FROM_DEVICE = 2,
+	SBI_DMA_NONE = 3,
+};
+
 enum sbi_hsm_hart_status {
 	SBI_HSM_HART_STATUS_STARTED = 0,
 	SBI_HSM_HART_STATUS_STOPPED,
@@ -128,6 +141,9 @@ int sbi_remote_hfence_vvma_asid(const unsigned long *hart_mask,
 				unsigned long size,
 				unsigned long asid);
 int sbi_probe_extension(int ext);
+void sbi_dma_sync(unsigned long start,
+		  unsigned long size,
+		  enum sbi_dma_sync_data_direction dir);
 
 /* Check if current SBI specification version is 0.1 or not */
 static inline int sbi_spec_is_0_1(void)
diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
index 7402a41..ff8e18b 100644
--- a/arch/riscv/kernel/sbi.c
+++ b/arch/riscv/kernel/sbi.c
@@ -521,6 +521,25 @@ int sbi_probe_extension(int extid)
 }
 EXPORT_SYMBOL(sbi_probe_extension);
 
+void sbi_dma_sync(unsigned long start,
+		  unsigned long size,
+		  enum sbi_dma_sync_data_direction dir)
+{
+#if 0
+	sbi_ecall(SBI_EXT_DMA, SBI_DMA_SYNC, start, size, dir,
+		  0, 0, 0);
+#else
+	/* Just for try, it should be in sbi ecall and will be removed before merged */
+	register unsigned long i asm("a0") = start & ~(L1_CACHE_BYTES - 1);
+
+	for (; i < (start + size); i += L1_CACHE_BYTES)
+		__asm__ __volatile__(".long 0x02b5000b");
+
+	__asm__ __volatile__(".long 0x01b0000b");
+#endif
+}
+EXPORT_SYMBOL(sbi_dma_sync);
+
 static long __sbi_base_ecall(int fid)
 {
 	struct sbiret ret;
diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
index 7ebaef1..b67d956 100644
--- a/arch/riscv/mm/Makefile
+++ b/arch/riscv/mm/Makefile
@@ -14,6 +14,10 @@ obj-$(CONFIG_MMU) += fault.o pageattr.o
 obj-y += cacheflush.o
 obj-y += context.o
 
+ifeq ($(CONFIG_RISCV_DMA_COHERENT), y)
+obj-y += dma-mapping.o
+endif
+
 ifeq ($(CONFIG_MMU),y)
 obj-$(CONFIG_SMP) += tlbflush.o
 endif
diff --git a/arch/riscv/mm/dma-mapping.c b/arch/riscv/mm/dma-mapping.c
new file mode 100644
index 00000000..f5db60b
--- /dev/null
+++ b/arch/riscv/mm/dma-mapping.c
@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/dma-map-ops.h>
+#include <asm/sbi.h>
+
+void arch_dma_prep_coherent(struct page *page, size_t size)
+{
+	void *ptr = page_address(page);
+
+	memset(ptr, 0, size);
+	sbi_dma_sync(page_to_phys(page), size, SBI_DMA_BIDIRECTIONAL);
+}
+
+void arch_sync_dma_for_device(phys_addr_t paddr, size_t size,
+		enum dma_data_direction dir)
+{
+	switch (dir) {
+	case DMA_TO_DEVICE:
+	case DMA_FROM_DEVICE:
+	case DMA_BIDIRECTIONAL:
+		sbi_dma_sync(paddr, size, dir);
+		break;
+	default:
+		BUG();
+	}
+}
+
+void arch_sync_dma_for_cpu(phys_addr_t paddr, size_t size,
+		enum dma_data_direction dir)
+{
+	switch (dir) {
+	case DMA_TO_DEVICE:
+		return;
+	case DMA_FROM_DEVICE:
+	case DMA_BIDIRECTIONAL:
+		sbi_dma_sync(paddr, size, dir);
+		break;
+	default:
+		BUG();
+	}
+}
-- 
2.7.4