[PATCH v4 4/6] mm: ioremap: Add ioremap/iounmap_allowed()

[Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>]

Add special hook for architecture to verify addr, size or prot
when ioremap() or iounmap(), which will make the generic ioremap
more useful.

  ioremap_allowed() return an int,
    - NULL means continue to remap
    - error code means skip remap and return directly
  iounmap_allowed() return an int,
    - 0 means continue to vunmap
    - error code means skip vunmap and return directly

Acked-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
---
 include/asm-generic/io.h | 25 +++++++++++++++++++++++++
 mm/ioremap.c             | 13 ++++++++++---
 2 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
index e6ffa2519f08..9429387a3e65 100644
--- a/include/asm-generic/io.h
+++ b/include/asm-generic/io.h
@@ -964,6 +964,31 @@ static inline void iounmap(volatile void __iomem *addr)
 #elif defined(CONFIG_GENERIC_IOREMAP)
 #include <linux/pgtable.h>
 
+/*
+ * Arch code can implement the following two special hooks when using GENERIC_IOREMAP
+ * ioremap_allowed() return an int,
+ *   - 0 means continue to remap
+ *   - error code means skip remap and return directly
+ * iounmap_allowed() return an int,
+ *   - 0 means continue to vunmap
+ *   - error code means skip vunmap and return directly
+ */
+#ifndef ioremap_allowed
+#define ioremap_allowed ioremap_allowed
+static inline int ioremap_allowed(phys_addr_t phys_addr, size_t size, unsigned long prot)
+{
+	return 0;
+}
+#endif
+
+#ifndef iounmap_allowed
+#define iounmap_allowed iounmap_allowed
+static inline int iounmap_allowed(void __iomem *addr)
+{
+	return 0;
+}
+#endif
+
 void __iomem *ioremap_prot(phys_addr_t phys_addr, size_t size, unsigned long prot);
 void iounmap(volatile void __iomem *addr);
 
diff --git a/mm/ioremap.c b/mm/ioremap.c
index 7cb9996b0c12..196c93c0beb8 100644
--- a/mm/ioremap.c
+++ b/mm/ioremap.c
@@ -27,8 +27,10 @@ void __iomem *ioremap_prot(phys_addr_t phys_addr, size_t size, unsigned long pro
 	phys_addr -= offset;
 	size = PAGE_ALIGN(size + offset);
 
-	area = get_vm_area_caller(size, VM_IOREMAP,
-			__builtin_return_address(0));
+	if (ioremap_allowed(phys_addr, size, prot))
+		return NULL;
+
+	area = get_vm_area_caller(size, VM_IOREMAP, __builtin_return_address(0));
 	if (!area)
 		return NULL;
 	vaddr = (unsigned long)area->addr;
@@ -45,6 +47,11 @@ EXPORT_SYMBOL(ioremap_prot);
 
 void iounmap(volatile void __iomem *addr)
 {
-	vunmap((void *)((unsigned long)addr & PAGE_MASK));
+	void __iomem *vaddr = (void __iomem *)((unsigned long)addr & PAGE_MASK);
+
+	if (iounmap_allowed(vaddr))
+		return;
+
+	vunmap((void __force *)vaddr);
 }
 EXPORT_SYMBOL(iounmap);
-- 
2.35.3