linux-kernel - [PATCH 2/2] ARM: dma-mapping: allow larger DMA mask than supported

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Date:   Tue, 21 May 2019 14:47:29 +0200
From:   Christoph Hellwig <hch@....de>
To:     iommu@...ts.linux-foundation.org,
        Russell King <linux@...linux.org.uk>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] ARM: dma-mapping: allow larger DMA mask than supported

Since Linux 5.1 we allow drivers to just set the largest DMA mask they
support instead of falling back to smaller ones.

When fixing up all the dma ops instances to allow for this behavior
the arm direct mapping code was missed.  Fix it up by removing the
sanity check, as all the actual mapping code handles this case just
fine.

Fixes: 9eb9e96e97b3 ("Documentation/DMA-API-HOWTO: update dma_mask sections")
Signed-off-by: Christoph Hellwig <hch@....de>
---
 arch/arm/mm/dma-mapping.c | 20 +-------------------
 1 file changed, 1 insertion(+), 19 deletions(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 0a75058c11f3..bdf0d236aaee 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -219,25 +219,7 @@ EXPORT_SYMBOL(arm_coherent_dma_ops);
 
 static int __dma_supported(struct device *dev, u64 mask, bool warn)
 {
-	unsigned long max_dma_pfn;
-
-	/*
-	 * If the mask allows for more memory than we can address,
-	 * and we actually have that much memory, then we must
-	 * indicate that DMA to this device is not supported.
-	 */
-	if (sizeof(mask) != sizeof(dma_addr_t) &&
-	    mask > (dma_addr_t)~0 &&
-	    dma_to_pfn(dev, ~0) < max_pfn - 1) {
-		if (warn) {
-			dev_warn(dev, "Coherent DMA mask %#llx is larger than dma_addr_t allows\n",
-				 mask);
-			dev_warn(dev, "Driver did not use or check the return value from dma_set_coherent_mask()?\n");
-		}
-		return 0;
-	}
-
-	max_dma_pfn = min(max_pfn, arm_dma_pfn_limit);
+	unsigned long max_dma_pfn = min(max_pfn, arm_dma_pfn_limit);
 
 	/*
 	 * Translate the device's DMA mask to a PFN limit.  This
-- 
2.20.1