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

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Date:   Mon, 27 Mar 2023 14:13:00 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     Arnd Bergmann <arnd@...db.de>, Vineet Gupta <vgupta@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Guo Ren <guoren@...nel.org>,
        Brian Cain <bcain@...cinc.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Michal Simek <monstr@...str.eu>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Stafford Horne <shorne@...il.com>,
        Helge Deller <deller@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Rich Felker <dalias@...c.org>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        "David S. Miller" <davem@...emloft.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        Christoph Hellwig <hch@....de>,
        Robin Murphy <robin.murphy@....com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        linux-snps-arc@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-oxnas@...ups.io,
        linux-csky@...r.kernel.org, linux-hexagon@...r.kernel.org,
        linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
        linux-openrisc@...r.kernel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-xtensa@...ux-xtensa.org
Subject: [PATCH 04/21] microblaze: dma-mapping: skip extra DMA flushes

From: Arnd Bergmann <arnd@...db.de>

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 <arnd@...db.de>
---
 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