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cma: use macro PFN_DOWN when converting size to pages

PATCH In review Xishi Qiu 2 participants 2 messages Aug 5, 2013

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Xishi Qiu

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#0 lore raw

PATCH v2 1/1 cma: use macro PFN_DOWN when converting size to pages

Use "PFN_DOWN(r->size)" instead of "r->size >> PAGE_SHIFT".

Signed-off-by Xishi Qiu <[email protected]>
---
 drivers/base/dma-contiguous.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)
drivers/base/dma-contiguous.c +1 -2
index 0ca5442..b3d711d 100644
@@ -206,8 +206,7 @@ static int __init cma_init_reserved_areas(void)
 
 	for (; i; --i, ++r) {
 		struct cma *cma;
-		cma = cma_create_area(PFN_DOWN(r->start),
-				      r->size >> PAGE_SHIFT);
+		cma = cma_create_area(PFN_DOWN(r->start), PFN_DOWN(r->size));
 		if (!IS_ERR(cma))
 			dev_set_cma_area(r->dev, cma);
 	}
Signature · 1 line
1.7.1
#1 lore raw
Quoted 12 lines · Xishi Qiu

Use "PFN_DOWN(r->size)" instead of "r->size >> PAGE_SHIFT".

Signed-off-by Xishi Qiu <[email protected]>
---
 drivers/base/dma-contiguous.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)
drivers/base/dma-contiguous.c +0 -0
index 0ca5442..b3d711d 100644

drivers/base/dma-contiguous.c static int __init cma_init_reserved_areas(void) · line 209

Quoted 6 lines
drivers/base/dma-contiguous.c +1 -2
@@ -206,8 +206,7 @@ static int __init cma_init_reserved_areas(void)
 
 	for (; i; --i, ++r) {
 		struct cma *cma;
-		cma = cma_create_area(PFN_DOWN(r->start),
-				      r->size >> PAGE_SHIFT);
+		cma = cma_create_area(PFN_DOWN(r->start), PFN_DOWN(r->size));

PFN_DOWN(r->start) makes sense because you are dividing and rounding a byte-granular address to a PFN.

r->size >> PAGE_SHIFT translates number of bytes into number of pages.

It ends up being the same arithmetic operation to do both things, but the units are different; the result of the second expression is not a PFN. I think this change actually worsens readability of the code.

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