Subject: [PATCH 04/21] microblaze: dma-mapping: skip extra DMA flushes

From: Arnd Bergmann <[email-masked]>
Date: Mon, 27 Mar 2023 14:13:00 +0200

From: Arnd Bergmann <[email-masked]>

The microblaze dma_sync_* implementation uses the same function
for both _for_cpu() and _for_device(), which is inconsistent
with other architectures and slightly more expensive.

Split it up into separate functions and skip the parts that
are not needed:

 - on dma_sync_*_for_cpu(..., DMA_TO_DEVICE), skip the second
   writeback, which does nothing.

 - on dma_sync_*_for_cpu(..., DMA_BIDIRECTIONAL), only invalidate
   the cache to clear out cache lines that got loaded speculatively,
   but skip the extraneous writeback.

Signed-off-by: Arnd Bergmann <[email-masked]>
---
 arch/microblaze/kernel/dma.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/arch/microblaze/kernel/dma.c b/arch/microblaze/kernel/dma.c
index 04d091ade417..b4c4e45fd45e 100644
--- a/arch/microblaze/kernel/dma.c
+++ b/arch/microblaze/kernel/dma.c
@@ -14,8 +14,8 @@
 #include <linux/bug.h>
 #include <asm/cacheflush.h>
 
-static void __dma_sync(phys_addr_t paddr, size_t size,
-		enum dma_data_direction direction)
+void arch_sync_dma_for_device(phys_addr_t paddr, size_t size,
+		enum dma_data_direction dir)
 {
 	switch (direction) {
 	case DMA_TO_DEVICE:
@@ -30,14 +30,16 @@ static void __dma_sync(phys_addr_t paddr, size_t size,
 	}
 }
 
-void arch_sync_dma_for_device(phys_addr_t paddr, size_t size,
-		enum dma_data_direction dir)
-{
-	__dma_sync(paddr, size, dir);
-}
-
 void arch_sync_dma_for_cpu(phys_addr_t paddr, size_t size,
 		enum dma_data_direction dir)
 {
-	__dma_sync(paddr, size, dir);
-}
+	switch (direction) {
+	case DMA_TO_DEVICE:
+		break;
+	case DMA_BIDIRECTIONAL:
+	case DMA_FROM_DEVICE:
+		invalidate_dcache_range(paddr, paddr + size);
+		break;
+	default:
+		BUG();
+	}}
-- 
2.39.2