Ok, here is patch which set Revision field (global variable system_rev) in /proc/cpuinfo from DT 
revision property:

diff --git a/arch/arm/kernel/devtree.c b/arch/arm/kernel/devtree.c
index 11c54de..9946c1b 100644
--- a/arch/arm/kernel/devtree.c
+++ b/arch/arm/kernel/devtree.c
@@ -19,6 +19,7 @@
 #include <linux/of_irq.h>
 #include <linux/of_platform.h>
 #include <linux/smp.h>
+#include <linux/libfdt_env.h>
 
 #include <asm/cputype.h>
 #include <asm/setup.h>
@@ -26,6 +27,7 @@
 #include <asm/smp_plat.h>
 #include <asm/mach/arch.h>
 #include <asm/mach-types.h>
+#include <asm/system_info.h>
 
 
 #ifdef CONFIG_SMP
@@ -204,6 +206,8 @@ static const void * __init arch_get_next_mach(const char *const **match)
 const struct machine_desc * __init setup_machine_fdt(unsigned int dt_phys)
 {
 	const struct machine_desc *mdesc, *mdesc_best = NULL;
+	unsigned long dt_root;
+	const u32 *prop;
 
 #ifdef CONFIG_ARCH_MULTIPLATFORM
 	DT_MACHINE_START(GENERIC_DT, "Generic DT based system")
@@ -215,17 +219,16 @@ const struct machine_desc * __init setup_machine_fdt(unsigned int dt_phys)
 	if (!dt_phys || !early_init_dt_verify(phys_to_virt(dt_phys)))
 		return NULL;
 
+	dt_root = of_get_flat_dt_root();
 	mdesc = of_flat_dt_match_machine(mdesc_best, arch_get_next_mach);
 
 	if (!mdesc) {
 		const char *prop;
 		int size;
-		unsigned long dt_root;
 
 		early_print("\nError: unrecognized/unsupported "
 			    "device tree compatible list:\n[ ");
 
-		dt_root = of_get_flat_dt_root();
 		prop = of_get_flat_dt_prop(dt_root, "compatible", &size);
 		while (size > 0) {
 			early_print("'%s' ", prop);
@@ -246,5 +249,10 @@ const struct machine_desc * __init setup_machine_fdt(unsigned int dt_phys)
 	/* Change machine number to match the mdesc we're using */
 	__machine_arch_type = mdesc->nr;
 
+	/* Set system revision from DT */
+	prop = of_get_flat_dt_prop(dt_root, "revision", NULL);
+	if (prop)
+		system_rev = fdt32_to_cpu(*prop);
+
 	return mdesc;
 }


And here is patch which convert ATAG revision into DT revision property and append it into DT in 
decompress code:

diff --git a/arch/arm/boot/compressed/atags_to_fdt.c b/arch/arm/boot/compressed/atags_to_fdt.c
index 9448aa0..e7e1cc9 100644
--- a/arch/arm/boot/compressed/atags_to_fdt.c
+++ b/arch/arm/boot/compressed/atags_to_fdt.c
@@ -171,6 +171,8 @@ int atags_to_fdt(void *atag_list, void *fdt, int total_space)
 					cpu_to_fdt32(atag->u.mem.size);
 			}
 
+		} else if (atag->hdr.tag == ATAG_REVISION) {
+			setprop_cell(fdt, "/", "revision", atag->u.revision.rev);
 		} else if (atag->hdr.tag == ATAG_INITRD2) {
 			uint32_t initrd_start, initrd_size;
 			initrd_start = atag->u.initrd.start;


I tested it on DT booted Nokia N900 and it is working, in /proc/cpuinfo is revision from ATAG.

I do not know which DT property to use for storing HW Revision, so if "/revision" is not correct one, 
let me know what to use instead. Also you can add my Signed-off-by for both patches.

-- 
Pali Rohár
pali.rohar@gmail.com