This function, being a variant of walk_system_ram_res() introduced in
commit 8c86e70acead ("resource: provide new functions to walk through
resources"), walks through a list of all the resources of System RAM
in reversed order, i.e., from higher to lower.

It will be used in kexec_file implementation on arm64.

Signed-off-by: AKASHI Takahiro <takahiro.aka...@linaro.org>
Cc: Vivek Goyal <vgo...@redhat.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Linus Torvalds <torva...@linux-foundation.org>
---
 include/linux/ioport.h |  3 +++
 kernel/resource.c      | 57 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+)

diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index da0ebaec25f0..f12d95fe038b 100644
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -277,6 +277,9 @@ extern int
 walk_system_ram_res(u64 start, u64 end, void *arg,
                    int (*func)(struct resource *, void *));
 extern int
+walk_system_ram_res_rev(u64 start, u64 end, void *arg,
+                       int (*func)(struct resource *, void *));
+extern int
 walk_iomem_res_desc(unsigned long desc, unsigned long flags, u64 start, u64 
end,
                    void *arg, int (*func)(struct resource *, void *));
 
diff --git a/kernel/resource.c b/kernel/resource.c
index e270b5048988..bdaa93407f4c 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -23,6 +23,8 @@
 #include <linux/pfn.h>
 #include <linux/mm.h>
 #include <linux/resource_ext.h>
+#include <linux/string.h>
+#include <linux/vmalloc.h>
 #include <asm/io.h>
 
 
@@ -486,6 +488,61 @@ int walk_mem_res(u64 start, u64 end, void *arg,
                                     arg, func);
 }
 
+int walk_system_ram_res_rev(u64 start, u64 end, void *arg,
+                               int (*func)(struct resource *, void *))
+{
+       struct resource res, *rams;
+       int rams_size = 16, i;
+       int ret = -1;
+
+       /* create a list */
+       rams = vmalloc(sizeof(struct resource) * rams_size);
+       if (!rams)
+               return ret;
+
+       res.start = start;
+       res.end = end;
+       res.flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
+       i = 0;
+       while ((res.start < res.end) &&
+               (!find_next_iomem_res(&res, IORES_DESC_NONE, true))) {
+               if (i >= rams_size) {
+                       /* re-alloc */
+                       struct resource *rams_new;
+                       int rams_new_size;
+
+                       rams_new_size = rams_size + 16;
+                       rams_new = vmalloc(sizeof(struct resource)
+                                                       * rams_new_size);
+                       if (!rams_new)
+                               goto out;
+
+                       memcpy(rams_new, rams,
+                                       sizeof(struct resource) * rams_size);
+                       vfree(rams);
+                       rams = rams_new;
+                       rams_size = rams_new_size;
+               }
+
+               rams[i].start = res.start;
+               rams[i++].end = res.end;
+
+               res.start = res.end + 1;
+               res.end = end;
+       }
+
+       /* go reverse */
+       for (i--; i >= 0; i--) {
+               ret = (*func)(&rams[i], arg);
+               if (ret)
+                       break;
+       }
+
+out:
+       vfree(rams);
+       return ret;
+}
+
 #if !defined(CONFIG_ARCH_HAS_WALK_MEMORY)
 
 /*
-- 
2.16.2

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