linux-kernel - [PATCH 2/2] dma-direct: only limit the mapping size if swiotlb could be used

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Date:   Wed, 17 Jul 2019 08:26:15 +0200
From:   Christoph Hellwig <hch@....de>
To:     iommu@...ts.linux-foundation.org
Cc:     Joerg Roedel <joro@...tes.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] dma-direct: only limit the mapping size if swiotlb could be used

Don't just check for a swiotlb buffer, but also if buffering might
be required for this particular device.

Fixes: 133d624b1cee ("dma: Introduce dma_max_mapping_size()")
Reported-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Signed-off-by: Christoph Hellwig <hch@....de>
Tested-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
---
 kernel/dma/direct.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index d7cec866d16b..e269b6f9b444 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -399,11 +399,9 @@ int dma_direct_supported(struct device *dev, u64 mask)
 
 size_t dma_direct_max_mapping_size(struct device *dev)
 {
-	size_t size = SIZE_MAX;
-
 	/* If SWIOTLB is active, use its maximum mapping size */
-	if (is_swiotlb_active())
-		size = swiotlb_max_mapping_size(dev);
-
-	return size;
+	if (is_swiotlb_active() &&
+	    (dma_addressing_limited(dev) || swiotlb_force == SWIOTLB_FORCE))
+		return swiotlb_max_mapping_size(dev);
+	return SIZE_MAX;
 }
-- 
2.20.1