riscv: mm: dma-noncoherent: nonstandard cache operations support

Introduce support for nonstandard noncoherent systems in the RISC-V
architecture. It enables function pointer support to handle cache
management in such systems.

This patch adds a new configuration option called
"RISCV_NONSTANDARD_CACHE_OPS." This option is a boolean flag that
depends on "RISCV_DMA_NONCOHERENT" and enables the function pointer
support for cache management in nonstandard noncoherent systems.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Tested-by: Conor Dooley <conor.dooley@microchip.com> # tyre-kicking on a d1
Reviewed-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Tested-by: Emil Renner Berthing <emil.renner.berthing@canonical.com> #
Link: https://lore.kernel.org/r/20230818135723.80612-4-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/Kconfig

@@ -269,6 +269,13 @@ config RISCV_DMA_NONCOHERENT
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE
 	select DMA_DIRECT_REMAP
 
+config RISCV_NONSTANDARD_CACHE_OPS
+	bool
+	depends on RISCV_DMA_NONCOHERENT
+	help
+	  This enables function pointer support for non-standard noncoherent
+	  systems to handle cache management.
+
 config AS_HAS_INSN
 	def_bool $(as-instr,.insn r 51$(comma) 0$(comma) 0$(comma) t0$(comma) t0$(comma) zero)
 

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

@@ -0,0 +1,28 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2023 Renesas Electronics Corp.
+ */
+
+#ifndef __ASM_DMA_NONCOHERENT_H
+#define __ASM_DMA_NONCOHERENT_H
+
+#include <linux/dma-direct.h>
+
+/*
+ * struct riscv_nonstd_cache_ops - Structure for non-standard CMO function pointers
+ *
+ * @wback: Function pointer for cache writeback
+ * @inv: Function pointer for invalidating cache
+ * @wback_inv: Function pointer for flushing the cache (writeback + invalidating)
+ */
+struct riscv_nonstd_cache_ops {
+	void (*wback)(phys_addr_t paddr, size_t size);
+	void (*inv)(phys_addr_t paddr, size_t size);
+	void (*wback_inv)(phys_addr_t paddr, size_t size);
+};
+
+extern struct riscv_nonstd_cache_ops noncoherent_cache_ops;
+
+void riscv_noncoherent_register_cache_ops(const struct riscv_nonstd_cache_ops *ops);
+
+#endif	/* __ASM_DMA_NONCOHERENT_H */

arch/riscv/mm/dma-noncoherent.c

@@ -9,13 +9,26 @@
 #include <linux/dma-map-ops.h>
 #include <linux/mm.h>
 #include <asm/cacheflush.h>
+#include <asm/dma-noncoherent.h>
 
 static bool noncoherent_supported __ro_after_init;
 
+struct riscv_nonstd_cache_ops noncoherent_cache_ops __ro_after_init = {
+	.wback = NULL,
+	.inv = NULL,
+	.wback_inv = NULL,
+};
+
 static inline void arch_dma_cache_wback(phys_addr_t paddr, size_t size)
 {
 	void *vaddr = phys_to_virt(paddr);
 
+#ifdef CONFIG_RISCV_NONSTANDARD_CACHE_OPS
+	if (unlikely(noncoherent_cache_ops.wback)) {
+		noncoherent_cache_ops.wback(paddr, size);
+		return;
+	}
+#endif
 	ALT_CMO_OP(clean, vaddr, size, riscv_cbom_block_size);
 }
 
@@ -23,6 +36,13 @@ static inline void arch_dma_cache_inv(phys_addr_t paddr, size_t size)
 {
 	void *vaddr = phys_to_virt(paddr);
 
+#ifdef CONFIG_RISCV_NONSTANDARD_CACHE_OPS
+	if (unlikely(noncoherent_cache_ops.inv)) {
+		noncoherent_cache_ops.inv(paddr, size);
+		return;
+	}
+#endif
+
 	ALT_CMO_OP(inval, vaddr, size, riscv_cbom_block_size);
 }
 
@@ -30,6 +50,13 @@ static inline void arch_dma_cache_wback_inv(phys_addr_t paddr, size_t size)
 {
 	void *vaddr = phys_to_virt(paddr);
 
+#ifdef CONFIG_RISCV_NONSTANDARD_CACHE_OPS
+	if (unlikely(noncoherent_cache_ops.wback_inv)) {
+		noncoherent_cache_ops.wback_inv(paddr, size);
+		return;
+	}
+#endif
+
 	ALT_CMO_OP(flush, vaddr, size, riscv_cbom_block_size);
 }
 
@@ -95,6 +122,13 @@ void arch_dma_prep_coherent(struct page *page, size_t size)
 {
 	void *flush_addr = page_address(page);
 
+#ifdef CONFIG_RISCV_NONSTANDARD_CACHE_OPS
+	if (unlikely(noncoherent_cache_ops.wback_inv)) {
+		noncoherent_cache_ops.wback_inv(page_to_phys(page), size);
+		return;
+	}
+#endif
+
 	ALT_CMO_OP(flush, flush_addr, size, riscv_cbom_block_size);
 }
 
@@ -120,3 +154,12 @@ void riscv_noncoherent_supported(void)
 	     "Non-coherent DMA support enabled without a block size\n");
 	noncoherent_supported = true;
 }
+
+void riscv_noncoherent_register_cache_ops(const struct riscv_nonstd_cache_ops *ops)
+{
+	if (!ops)
+		return;
+
+	noncoherent_cache_ops = *ops;
+}
+EXPORT_SYMBOL_GPL(riscv_noncoherent_register_cache_ops);

arch/riscv/mm/pmem.c

@@ -7,15 +7,28 @@
 #include <linux/libnvdimm.h>
 
 #include <asm/cacheflush.h>
+#include <asm/dma-noncoherent.h>
 
 void arch_wb_cache_pmem(void *addr, size_t size)
 {
+#ifdef CONFIG_RISCV_NONSTANDARD_CACHE_OPS
+	if (unlikely(noncoherent_cache_ops.wback)) {
+		noncoherent_cache_ops.wback(virt_to_phys(addr), size);
+		return;
+	}
+#endif
 	ALT_CMO_OP(clean, addr, size, riscv_cbom_block_size);
 }
 EXPORT_SYMBOL_GPL(arch_wb_cache_pmem);
 
 void arch_invalidate_pmem(void *addr, size_t size)
 {
+#ifdef CONFIG_RISCV_NONSTANDARD_CACHE_OPS
+	if (unlikely(noncoherent_cache_ops.inv)) {
+		noncoherent_cache_ops.inv(virt_to_phys(addr), size);
+		return;
+	}
+#endif
 	ALT_CMO_OP(inval, addr, size, riscv_cbom_block_size);
 }
 EXPORT_SYMBOL_GPL(arch_invalidate_pmem);