linux-kernel - [PATCH 1/2] arm64/mm: check cpu cache line size with non-coherent device

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Date:   Tue, 11 Jun 2019 11:17:30 -0400
From:   Masayoshi Mizuma <msys.mizuma@...il.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     Masayoshi Mizuma <msys.mizuma@...il.com>,
        Masayoshi Mizuma <m.mizuma@...fujitsu.com>,
        linux-kernel@...r.kernel.org,
        Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
        Zhang Lei <zhang.lei@...fujitsu.com>
Subject: [PATCH 1/2] arm64/mm: check cpu cache line size with non-coherent device

From: Masayoshi Mizuma <m.mizuma@...fujitsu.com>

As discussed in the thread [1], the cpu cache line size will be problem
only on non-coherent devices. And, the coherent flag is already introduced
to struct device.

Show the warning only if the device is non-coherent device and
ARCH_DMA_MINALIGN is smaller than the cpu cache size.

[1] https://lore.kernel.org/linux-arm-kernel/20180514145703.celnlobzn3uh5tc2@localhost/

Signed-off-by: Masayoshi Mizuma <m.mizuma@...fujitsu.com>
Reviewed-by: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
Tested-by: Zhang Lei <zhang.lei@...fujitsu.com>
---
 arch/arm64/mm/dma-mapping.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index 674860e3e478..c0c09890c845 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c
@@ -91,10 +91,6 @@ static int __swiotlb_mmap_pfn(struct vm_area_struct *vma,
 
 static int __init arm64_dma_init(void)
 {
-	WARN_TAINT(ARCH_DMA_MINALIGN < cache_line_size(),
-		   TAINT_CPU_OUT_OF_SPEC,
-		   "ARCH_DMA_MINALIGN smaller than CTR_EL0.CWG (%d < %d)",
-		   ARCH_DMA_MINALIGN, cache_line_size());
 	return dma_atomic_pool_init(GFP_DMA32, __pgprot(PROT_NORMAL_NC));
 }
 arch_initcall(arm64_dma_init);
@@ -473,6 +469,11 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
 			const struct iommu_ops *iommu, bool coherent)
 {
 	dev->dma_coherent = coherent;
+
+	if (!coherent && (cache_line_size() > ARCH_DMA_MINALIGN))
+		dev_WARN(dev, "ARCH_DMA_MINALIGN smaller than CTR_EL0.CWG (%d < %d)",
+				ARCH_DMA_MINALIGN, cache_line_size());
+
 	__iommu_setup_dma_ops(dev, dma_base, size, iommu);
 
 #ifdef CONFIG_XEN
-- 
2.20.1