From c44094eee32f32f175aadc0efcac449d99b1bbf7 Mon Sep 17 00:00:00 2001
From: Will Deacon <will@kernel.org>
Date: Tue, 23 Aug 2022 13:21:11 +0100
Subject: [PATCH] arm64: dma: Drop cache invalidation from
arch_dma_prep_coherent()
arch_dma_prep_coherent() is called when preparing a non-cacheable region
for a consistent DMA buffer allocation. Since the buffer pages may
previously have been written via a cacheable mapping and consequently
allocated as dirty cachelines, the purpose of this function is to remove
these dirty lines from the cache, writing them back so that the
non-coherent device is able to see them.
On arm64, this operation can be achieved with a clean to the point of
coherency; a subsequent invalidation is not required and serves little
purpose in the presence of a cacheable alias (e.g. the linear map),
since clean lines can be speculatively fetched back into the cache after
the invalidation operation has completed.
Relax the cache maintenance in arch_dma_prep_coherent() so that only a
clean, and not a clean-and-invalidate operation is performed.
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20220823122111.17439-1-will@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
---
arch/arm64/mm/dma-mapping.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index 599cf81f56851..83a512a6ff0dd 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c
@@ -36,7 +36,7 @@ void arch_dma_prep_coherent(struct page *page, size_t size)
{
unsigned long start = (unsigned long)page_address(page);
- dcache_clean_inval_poc(start, start + size);
+ dcache_clean_poc(start, start + size);
}
#ifdef CONFIG_IOMMU_DMA
--
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