powerpc/mem: Inline flush_dcache_page()

flush_dcache_page() is only a few lines, it is worth
inlining.

ia64, csky, mips, openrisc and riscv have a similar
flush_dcache_page() and inline it.

On pmac32_defconfig, we get a small size reduction.
On ppc64_defconfig, we get a very small size increase.

In both case that's in the noise (less than 0.1%).

text		data	bss	dec		hex	filename
18991155	5934744	1497624f	26423523	19330e3	vmlinux64.before
18994829	5936732	1497624f	26429185	1934701	vmlinux64.after
9150963		2467502	 184548	11803013	 b41985	vmlinux32.before
9149689		2467302	 184548	11801539	 b413c3	vmlinux32.after
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/21c417488b70b7629dae316539fb7bb8bdef4fdd.1617895813.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/cacheflush.h

@@ -30,7 +30,19 @@ static inline void flush_cache_vmap(unsigned long start, unsigned long end)
 #endif /* CONFIG_PPC_BOOK3S_64 */
 
 #define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE 1
-extern void flush_dcache_page(struct page *page);
+/*
+ * This is called when a page has been modified by the kernel.
+ * It just marks the page as not i-cache clean.  We do the i-cache
+ * flush later when the page is given to a user process, if necessary.
+ */
+static inline void flush_dcache_page(struct page *page)
+{
+	if (cpu_has_feature(CPU_FTR_COHERENT_ICACHE))
+		return;
+	/* avoid an atomic op if possible */
+	if (test_bit(PG_dcache_clean, &page->flags))
+		clear_bit(PG_dcache_clean, &page->flags);
+}
 
 void flush_icache_range(unsigned long start, unsigned long stop);
 #define flush_icache_range flush_icache_range

arch/powerpc/mm/cacheflush.c

@@ -121,21 +121,6 @@ static void flush_dcache_icache_phys(unsigned long physaddr)
 }
 #endif
 
-/*
- * This is called when a page has been modified by the kernel.
- * It just marks the page as not i-cache clean.  We do the i-cache
- * flush later when the page is given to a user process, if necessary.
- */
-void flush_dcache_page(struct page *page)
-{
-	if (cpu_has_feature(CPU_FTR_COHERENT_ICACHE))
-		return;
-	/* avoid an atomic op if possible */
-	if (test_bit(PG_dcache_clean, &page->flags))
-		clear_bit(PG_dcache_clean, &page->flags);
-}
-EXPORT_SYMBOL(flush_dcache_page);
-
 /**
  * __flush_dcache_icache(): Flush a particular page from the data cache to RAM.
  * Note: this is necessary because the instruction cache does *not*