Merge patch series "riscv: dma-mapping: unify support for cache flushes"

Prabhakar <prabhakar.csengg@gmail.com> says:

From: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>

This patch series is a subset from Arnd's original series [0]. Ive just
picked up the bits required for RISC-V unification of cache flushing.
Remaining patches from the series [0] will be taken care by Arnd soon.

* b4-shazam-merge:
  riscv: dma-mapping: switch over to generic implementation
  riscv: dma-mapping: skip invalidation before bidirectional DMA
  riscv: dma-mapping: only invalidate after DMA, not flush

Link: https://lore.kernel.org/r/20230816232336.164413-1-prabhakar.mahadev-lad.rj@bp.renesas.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/mm/dma-noncoherent.c

@@ -14,21 +14,61 @@ static bool noncoherent_supported __ro_after_init;
 int dma_cache_alignment __ro_after_init = ARCH_DMA_MINALIGN;
 EXPORT_SYMBOL_GPL(dma_cache_alignment);
 
-void arch_sync_dma_for_device(phys_addr_t paddr, size_t size,
-			      enum dma_data_direction dir)
+static inline void arch_dma_cache_wback(phys_addr_t paddr, size_t size)
+{
+	void *vaddr = phys_to_virt(paddr);
+
+	ALT_CMO_OP(clean, vaddr, size, riscv_cbom_block_size);
+}
+
+static inline void arch_dma_cache_inv(phys_addr_t paddr, size_t size)
 {
 	void *vaddr = phys_to_virt(paddr);
 
+	ALT_CMO_OP(inval, vaddr, size, riscv_cbom_block_size);
+}
+
+static inline void arch_dma_cache_wback_inv(phys_addr_t paddr, size_t size)
+{
+	void *vaddr = phys_to_virt(paddr);
+
+	ALT_CMO_OP(flush, vaddr, size, riscv_cbom_block_size);
+}
+
+static inline bool arch_sync_dma_clean_before_fromdevice(void)
+{
+	return true;
+}
+
+static inline bool arch_sync_dma_cpu_needs_post_dma_flush(void)
+{
+	return true;
+}
+
+void arch_sync_dma_for_device(phys_addr_t paddr, size_t size,
+			      enum dma_data_direction dir)
+{
 	switch (dir) {
 	case DMA_TO_DEVICE:
-		ALT_CMO_OP(clean, vaddr, size, riscv_cbom_block_size);
+		arch_dma_cache_wback(paddr, size);
 		break;
+
 	case DMA_FROM_DEVICE:
-		ALT_CMO_OP(clean, vaddr, size, riscv_cbom_block_size);
+		if (!arch_sync_dma_clean_before_fromdevice()) {
+			arch_dma_cache_inv(paddr, size);
 			break;
+		}
+		fallthrough;
+
 	case DMA_BIDIRECTIONAL:
-		ALT_CMO_OP(flush, vaddr, size, riscv_cbom_block_size);
+		/* Skip the invalidate here if it's done later */
+		if (IS_ENABLED(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU) &&
+		    arch_sync_dma_cpu_needs_post_dma_flush())
+			arch_dma_cache_wback(paddr, size);
+		else
+			arch_dma_cache_wback_inv(paddr, size);
 		break;
+
 	default:
 		break;
 	}
@@ -37,15 +77,17 @@ void arch_sync_dma_for_device(phys_addr_t paddr, size_t size,
 void arch_sync_dma_for_cpu(phys_addr_t paddr, size_t size,
 			   enum dma_data_direction dir)
 {
-	void *vaddr = phys_to_virt(paddr);
-
 	switch (dir) {
 	case DMA_TO_DEVICE:
 		break;
+
 	case DMA_FROM_DEVICE:
 	case DMA_BIDIRECTIONAL:
-		ALT_CMO_OP(flush, vaddr, size, riscv_cbom_block_size);
+		/* FROM_DEVICE invalidate needed if speculative CPU prefetch only */
+		if (arch_sync_dma_cpu_needs_post_dma_flush())
+			arch_dma_cache_inv(paddr, size);
 		break;
+
 	default:
 		break;
 	}