linux-kernel - [PATCH 2/3] dma-mapping: simplify dma_direct get_required

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Date:   Mon, 10 Sep 2018 08:13:31 +0200
From:   Christoph Hellwig <hch@....de>
To:     iommu@...ts.linux-foundation.org
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/3] dma-mapping: simplify dma_direct get_required_mask

If we use fls64 we don't need to divide the max address into lower
and upper halves.

Signed-off-by: Christoph Hellwig <hch@....de>
---
 drivers/base/platform.c | 18 +++---------------
 1 file changed, 3 insertions(+), 15 deletions(-)

diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index a255fc8aa483..7812b861b6da 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -1185,21 +1185,9 @@ int __init platform_bus_init(void)
  */
 u64 dma_direct_get_required_mask(struct device *dev)
 {
-	u32 low_totalram = ((max_pfn - 1) << PAGE_SHIFT);
-	u32 high_totalram = ((max_pfn - 1) >> (32 - PAGE_SHIFT));
-	u64 mask;
-
-	if (!high_totalram) {
-		/* convert to mask just covering totalram */
-		low_totalram = (1 << (fls(low_totalram) - 1));
-		low_totalram += low_totalram - 1;
-		mask = low_totalram;
-	} else {
-		high_totalram = (1 << (fls(high_totalram) - 1));
-		high_totalram += high_totalram - 1;
-		mask = (((u64)high_totalram) << 32) + 0xffffffff;
-	}
-	return mask;
+	u64 end = ((max_pfn - 1) << PAGE_SHIFT);
+
+	return (1 << (fls64(end) - 1)) * 2 - 1;
 }
 
 #ifndef ARCH_HAS_DMA_GET_REQUIRED_MASK
-- 
2.18.0