linux-kernel - [PATCH 13/21] arc: dma-mapping: skip invalidating before bidirectional DMA

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Message-Id: <20230327121317.4081816-14-arnd@kernel.org>
Date:   Mon, 27 Mar 2023 14:13:09 +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 13/21] arc: dma-mapping: skip invalidating before bidirectional DMA

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

Some architectures that need to invalidate buffers after bidirectional
DMA because of speculative prefetching only do a simpler writeback
before that DMA, while architectures that don't need to do the second
invalidate tend to have a combined writeback+invalidate before the
DMA.

arc is one of the architectures that does both, which seems unnecessary.

Change it to behave like arm/arm64/xtensa instead, and use just a
writeback before the DMA when we do the invalidate afterwards.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 arch/arc/mm/dma.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arc/mm/dma.c b/arch/arc/mm/dma.c
index 2a7fbbb83b70..ddb96786f765 100644
--- a/arch/arc/mm/dma.c
+++ b/arch/arc/mm/dma.c
@@ -40,7 +40,7 @@ void arch_dma_prep_coherent(struct page *page, size_t size)
  *          |----------------------------------------------------------------
  * TO_DEV   |   writeback        writeback      |   none          none
  * FROM_DEV |   invalidate       invalidate     |   invalidate*   invalidate*
- * BIDIR    |   writeback+inv    writeback+inv  |   invalidate    invalidate
+ * BIDIR    |   writeback        writeback      |   invalidate    invalidate
  *
  *     [*] needed for CPU speculative prefetches
  *
@@ -61,7 +61,7 @@ void arch_sync_dma_for_device(phys_addr_t paddr, size_t size,
 		break;
 
 	case DMA_BIDIRECTIONAL:
-		dma_cache_wback_inv(paddr, size);
+		dma_cache_wback(paddr, size);
 		break;
 
 	default:
-- 
2.39.2