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Subject[PATCH] dma-direct: Optimize get_required_mask
Date
Optimize dma_direct_get_required_mask(), in that we don't need to multiply by
two if we don't subtract 1 from the exponent. That is,

(1 << (n - 1)) * 2 - 1 <==>
2^(n-1) * 2^1 - 1 = (by rule of exponents)
2^n - 1 <==>
(1 << n) - 1.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Alex Deucher <Alexander.Deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: iommu@lists.linux.dev
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
---
kernel/dma/direct.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 63859a101ed831..bb416a3949dac0 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -41,7 +41,7 @@ u64 dma_direct_get_required_mask(struct device *dev)
phys_addr_t phys = (phys_addr_t)(max_pfn - 1) << PAGE_SHIFT;
u64 max_dma = phys_to_dma_direct(dev, phys);

- return (1ULL << (fls64(max_dma) - 1)) * 2 - 1;
+ return (1ULL << fls64(max_dma)) - 1;
}

static gfp_t dma_direct_optimal_gfp_mask(struct device *dev, u64 dma_mask,
base-commit: e2ca6ba6ba0152361aa4fcbf6067db71b2c7a770
--
2.39.0

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