linux-kernel - [PATCH v2] arm64/mm: Correct the cache line size warning with non coherent device

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Date:   Fri, 14 Jun 2019 09:11:41 -0400
From:   Masayoshi Mizuma <msys.mizuma@...il.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Robin Murphy <robin.murphy@....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 v2] arm64/mm: Correct the cache line size warning with non coherent device

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

If the cache line size is greater than ARCH_DMA_MINALIGN (128),
the warning shows and it's tainted as TAINT_CPU_OUT_OF_SPEC.

However, it's not good because as discussed in the thread [1], the cpu
cache line size will be problem only on non-coherent devices.

Since 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/include/asm/cache.h |  7 +++++++
 arch/arm64/kernel/cacheinfo.c  |  4 +---
 arch/arm64/mm/dma-mapping.c    | 14 ++++++++++----
 3 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/include/asm/cache.h b/arch/arm64/include/asm/cache.h
index 758af6340314..d24b7c1ecd9b 100644
--- a/arch/arm64/include/asm/cache.h
+++ b/arch/arm64/include/asm/cache.h
@@ -91,6 +91,13 @@ static inline u32 cache_type_cwg(void)
 
 #define __read_mostly __attribute__((__section__(".data..read_mostly")))
 
+static inline int cache_line_size_of_cpu(void)
+{
+	u32 cwg = cache_type_cwg();
+
+	return cwg ? 4 << cwg : ARCH_DMA_MINALIGN;
+}
+
 int cache_line_size(void);
 
 /*
diff --git a/arch/arm64/kernel/cacheinfo.c b/arch/arm64/kernel/cacheinfo.c
index 6eaf1c07aa4e..7fa6828bb488 100644
--- a/arch/arm64/kernel/cacheinfo.c
+++ b/arch/arm64/kernel/cacheinfo.c
@@ -19,12 +19,10 @@
 
 int cache_line_size(void)
 {
-	u32 cwg = cache_type_cwg();
-
 	if (coherency_max_size != 0)
 		return coherency_max_size;
 
-	return cwg ? 4 << cwg : ARCH_DMA_MINALIGN;
+	return cache_line_size_of_cpu();
 }
 EXPORT_SYMBOL_GPL(cache_line_size);
 
diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index 1669618db08a..379589dc7113 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c
@@ -38,10 +38,6 @@ void arch_dma_prep_coherent(struct page *page, size_t size)
 
 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);
@@ -56,7 +52,17 @@ void arch_teardown_dma_ops(struct device *dev)
 void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
 			const struct iommu_ops *iommu, bool coherent)
 {
+	int cls = cache_line_size_of_cpu();
+
 	dev->dma_coherent = coherent;
+
+	if (!coherent)
+		WARN_TAINT(cls > ARCH_DMA_MINALIGN,
+			TAINT_CPU_OUT_OF_SPEC,
+			"%s %s: ARCH_DMA_MINALIGN smaller than CTR_EL0.CWG (%d < %d)",
+			dev_driver_string(dev), dev_name(dev),
+			ARCH_DMA_MINALIGN, cls);
+
 	if (iommu)
 		iommu_setup_dma_ops(dev, dma_base, size);
 
-- 
2.20.1