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Subject[PATCH 5/5 v2] x86: PAT: make pat_x_mtrr_type() more readable
I've found it inconvenient to review pat_x_mtrr_type().
Thus I slightly changed it and added some comment to make
it more readable.

I've also added BUG statements for (some) unused/unhandled PAT/MTRR
types.

Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
---
New patch version. (against current tip/x86/pat - v2.6.26-rc6-105-gfaeca31)
Previous version had some conflict with another commit in tip/master.

Regards,
Andreas

arch/x86/mm/pat.c | 50 +++++++++++++++++++++++++++-----------------------
1 files changed, 27 insertions(+), 23 deletions(-)

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 4beccea..cdf2c15 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -169,35 +169,39 @@ static int pat_x_mtrr_type(u64 start, u64 end, unsigned long prot,
prot &= (~_PAGE_CACHE_MASK);

/*
- * We return the PAT request directly for types where PAT takes
- * precedence with respect to MTRR and for UC_MINUS.
+ * We return the PAT request directly for types where PAT
+ * takes precedence with respect to MTRR and for UC_MINUS. In
+ * case of pat_type==WB we have to know mtrr_type to get the
+ * effective type.
+ *
+ * effective type ret_prot
+ * pat \ mtrr WB WC UC pat \ mtrr WB WC UC
+ * WC WC WC WC WC WC WC WC
+ * UC- UC WC UC UC- UC- UC- UC-
+ * UC UC UC UC UC UC UC UC
+ * WB WB WC UC WB WB WC UC
+ *
* Consistency checks with other PAT requests is done later
* while going through memtype list.
*/
- if (pat_type == _PAGE_CACHE_WC) {
+ if (pat_type == _PAGE_CACHE_WC)
*ret_prot = prot | _PAGE_CACHE_WC;
- return 0;
- } else if (pat_type == _PAGE_CACHE_UC_MINUS) {
+ else if (pat_type == _PAGE_CACHE_UC_MINUS)
*ret_prot = prot | _PAGE_CACHE_UC_MINUS;
- return 0;
- } else if (pat_type == _PAGE_CACHE_UC) {
- *ret_prot = prot | _PAGE_CACHE_UC;
- return 0;
- }
-
- /*
- * Look for MTRR hint to get the effective type in case where PAT
- * request is for WB.
- */
- mtrr_type = mtrr_type_lookup(start, end);
-
- if (mtrr_type == MTRR_TYPE_UNCACHABLE) {
+ else if (pat_type == _PAGE_CACHE_UC)
*ret_prot = prot | _PAGE_CACHE_UC;
- } else if (mtrr_type == MTRR_TYPE_WRCOMB) {
- *ret_prot = prot | _PAGE_CACHE_WC;
- } else {
- *ret_prot = prot | _PAGE_CACHE_WB;
- }
+ else if (pat_type == _PAGE_CACHE_WB) {
+ mtrr_type = mtrr_type_lookup(start, end);
+ if (mtrr_type == MTRR_TYPE_WRBACK)
+ *ret_prot = prot | _PAGE_CACHE_WB;
+ else if (mtrr_type == MTRR_TYPE_WRCOMB)
+ *ret_prot = prot | _PAGE_CACHE_WC;
+ else if (mtrr_type == MTRR_TYPE_UNCACHABLE)
+ *ret_prot = prot | _PAGE_CACHE_UC;
+ else
+ BUG();
+ } else
+ BUG();

return 0;
}
--
1.5.5.4





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