[RFC PATCH 2/2] arm64: Use PoU cache instr for I/D coherency

[Ashok Kumar]

In systems with three levels of cache(PoU at L1 and PoC at L3),
PoC cache flush instructions flushes L2 and L3 caches which could affect
performance.
For cache flushes for I and D coherency, PoU should suffice.
So changing all I and D coherency related cache flushes to PoU.

Introduced a new __flush_dcache_area_pou API for dcache flush till PoU

Signed-off-by: Ashok Kumar <ashoks at broadcom.com>
---
 arch/arm64/include/asm/cacheflush.h |  1 +
 arch/arm64/mm/cache.S               | 22 ++++++++++++++++++++++
 arch/arm64/mm/flush.c               | 13 +++++++++----
 3 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/cacheflush.h b/arch/arm64/include/asm/cacheflush.h
index c75b8d0..e4b13f7 100644
--- a/arch/arm64/include/asm/cacheflush.h
+++ b/arch/arm64/include/asm/cacheflush.h
@@ -68,6 +68,7 @@
 extern void flush_cache_range(struct vm_area_struct *vma, unsigned long start, unsigned long end);
 extern void flush_icache_range(unsigned long start, unsigned long end);
 extern void __flush_dcache_area(void *addr, size_t len);
+extern void __flush_dcache_area_pou(void *addr, size_t len);
 extern long __flush_cache_user_range(unsigned long start, unsigned long end);
 
 static inline void flush_cache_mm(struct mm_struct *mm)
diff --git a/arch/arm64/mm/cache.S b/arch/arm64/mm/cache.S
index eb48d5d..037293c 100644
--- a/arch/arm64/mm/cache.S
+++ b/arch/arm64/mm/cache.S
@@ -101,6 +101,28 @@ ENTRY(__flush_dcache_area)
 ENDPROC(__flush_dcache_area)
 
 /*
+ *	__flush_dcache_area_pou(kaddr, size)
+ *
+ *	Ensure that the data held in the page kaddr is written back to the
+ *	page in question till Point of Unification.
+ *
+ *	- kaddr   - kernel address
+ *	- size    - size in question
+ */
+ENTRY(__flush_dcache_area_pou)
+	dcache_line_size x2, x3
+	add	x1, x0, x1
+	sub	x3, x2, #1
+	bic	x0, x0, x3
+1:	dc	cvau, x0			// clean D line till PoU
+	add	x0, x0, x2
+	cmp	x0, x1
+	b.lo	1b
+	dsb	sy
+	ret
+ENDPROC(__flush_dcache_area_pou)
+
+/*
  *	__inval_cache_range(start, end)
  *	- start   - start address of region
  *	- end     - end address of region
diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
index c26b804..6235af6 100644
--- a/arch/arm64/mm/flush.c
+++ b/arch/arm64/mm/flush.c
@@ -41,7 +41,7 @@ static void flush_ptrace_access(struct vm_area_struct *vma, struct page *page,
 	if (vma->vm_flags & VM_EXEC) {
 		unsigned long addr = (unsigned long)kaddr;
 		if (icache_is_aliasing()) {
-			__flush_dcache_area(kaddr, len);
+			__flush_dcache_area_pou(kaddr, len);
 			__flush_icache_all();
 		} else {
 			flush_icache_range(addr, addr + len);
@@ -75,9 +75,14 @@ void __sync_icache_dcache(pte_t pte, unsigned long addr)
 		return;
 
 	if (!test_and_set_bit(PG_dcache_clean, &page->flags)) {
-		__flush_dcache_area(page_address(page),
-				PAGE_SIZE << compound_order(page));
-		__flush_icache_all();
+		if (icache_is_aliasing()) {
+			__flush_dcache_area_pou(page_address(page),
+					    PAGE_SIZE << compound_order(page));
+			__flush_icache_all();
+		} else
+			flush_icache_range(page_address(page),
+					   page_address(page) +
+					   (PAGE_SIZE << compound_order(page)));
 	} else if (icache_is_aivivt()) {
 		__flush_icache_all();
 	}
-- 
2.1.0