include/asm-generic/pgtable.h: Check once and return for pgprot_modify

PATCH In review Chen Gang 1 participant 2 messages Dec 13, 2015 Generic include/asm header files

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Chen Gang

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2015-12-13 09:09 UTC #0 lore raw

PATCH 1/1 include/asm-generic/pgtable.h: Check once and return for pgprot_modify

pgprot_val() likes an empty operation, and all three checking statements are related with oldprot, so only check once is enough, the reason is:

- if both "oldprot == pgprot_noncached(oldprot)" and "oldprot == pgprot_writecombine(oldprot)" are satisfied.

- So "pgprot_noncached(oldprot) == pgprot_writecombine(oldprot)", too.

- So as the result, it is still equal to check once (for pgprot_device can get the same result).

Then can return directly.

Signed-off-by Chen Gang <[email protected]>

---
 include/asm-generic/pgtable.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

include/asm-generic/pgtable.h +3 -3

index 069536a..cd9e7c4 100644
@@ -306,11 +306,11 @@ static inline int pmd_same(pmd_t pmd_a, pmd_t pmd_b)
 static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
 {
 	if (pgprot_val(oldprot) == pgprot_val(pgprot_noncached(oldprot)))
-		newprot = pgprot_noncached(newprot);
+		return pgprot_noncached(newprot);
 	if (pgprot_val(oldprot) == pgprot_val(pgprot_writecombine(oldprot)))
-		newprot = pgprot_writecombine(newprot);
+		return pgprot_writecombine(newprot);
 	if (pgprot_val(oldprot) == pgprot_val(pgprot_device(oldprot)))
-		newprot = pgprot_device(newprot);
+		return pgprot_device(newprot);
 	return newprot;
 }
 #endif

Signature · 1 line

1.9.3

Chen Gang

author

2015-12-13 15:43 UTC #1 lore raw

Oh, after check again, it looks my original comments are not precise:
they check oldprot, but set newprot.

After check pgprot_noncached, pgprot_writecombine, and pgprot_device again, for me, if still in order: 1st noncached, 2nd writecombine, 3rd device, we can still treate them exclusive with each other:

- For pgprot_device, Only amd64 redefine it, which is exclusive with the others (or the precisely same as one of the others).

- For pgprot_writecombine, except metag and x86, all the other archs are exclusive with (or same as) pgprot_noncached.

for metag arch, pgprot_writecombine is the part of pgprot_noncached.

for x86 arch, it has its own pgprot_modify.

Thanks.

Quoted 39 lines · Chen Gang

pgprot_val() likes an empty operation, and all three checking statements are related with oldprot, so only check once is enough, the reason is:
- if both "oldprot == pgprot_noncached(oldprot)" and "oldprot == pgprot_writecombine(oldprot)" are satisfied.
- So "pgprot_noncached(oldprot) == pgprot_writecombine(oldprot)", too.
- So as the result, it is still equal to check once (for pgprot_device can get the same result).
Then can return directly.
Signed-off-by Chen Gang <[email protected]>
---
 include/asm-generic/pgtable.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
include/asm-generic/pgtable.h +3 -3
index 069536a..cd9e7c4 100644
@@ -306,11 +306,11 @@ static inline int pmd_same(pmd_t pmd_a, pmd_t pmd_b)
 static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
 {
 	if (pgprot_val(oldprot) == pgprot_val(pgprot_noncached(oldprot)))
-		newprot = pgprot_noncached(newprot);
+		return pgprot_noncached(newprot);
 	if (pgprot_val(oldprot) == pgprot_val(pgprot_writecombine(oldprot)))
-		newprot = pgprot_writecombine(newprot);
+		return pgprot_writecombine(newprot);
 	if (pgprot_val(oldprot) == pgprot_val(pgprot_device(oldprot)))
-		newprot = pgprot_device(newprot);
+		return pgprot_device(newprot);
 	return newprot;
 }
 #endif

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Chen Gang (陈刚)

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