openrisc: enable passing of flattened device tree pointer

This patch enables passing a fdt pointer to the kernel.

This makes for the kernel parameter API:

void kernel(unsigned int fdt);

which, in accordance with the OpenRISC ABI results in:
r3 = pointer to fdt

Signed-off-by: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Signed-off-by: Jonas Bonn <jonas@southpole.se>

2 files changed, 25 insertions, 10 deletions

diff --git a/arch/openrisc/kernel/head.S b/arch/openrisc/kernel/head.S
index c75018d22644..1088b5fca3bd 100644
--- a/arch/openrisc/kernel/head.S
+++ b/arch/openrisc/kernel/head.S
@@ -26,6 +26,7 @@
 #include <asm/cache.h>
 #include <asm/spr_defs.h>
 #include <asm/asm-offsets.h>
+#include <linux/of_fdt.h>
 
 #define tophys(rd,rs)                           \
         l.movhi rd,hi(-KERNELBASE)              ;\
@@ -440,6 +441,9 @@ _dispatch_do_ipage_fault:
         __HEAD
         .global _start
 _start:
+        /* save kernel parameters */
+        l.or    r25,r0,r3       /* pointer to fdt */
+
         /*
          * ensure a deterministic start
          */
@@ -471,7 +475,6 @@ _start:
         CLEAR_GPR(r22)
         CLEAR_GPR(r23)
         CLEAR_GPR(r24)
-        CLEAR_GPR(r25)
         CLEAR_GPR(r26)
         CLEAR_GPR(r27)
         CLEAR_GPR(r28)
@@ -565,6 +568,18 @@ enable_mmu:
         // reset the simulation counters
         l.nop 5
 
+        /* check fdt header magic word */
+        l.lwz   r3,0(r25)       /* load magic from fdt into r3 */
+        l.movhi r4,hi(OF_DT_HEADER)
+        l.ori   r4,r4,lo(OF_DT_HEADER)
+        l.sfeq  r3,r4
+        l.bf    _fdt_found
+         l.nop
+        /* magic number mismatch, set fdt pointer to null */
+        l.or    r25,r0,r0
+_fdt_found:
+        /* pass fdt pointer to or32_early_setup in r3 */
+        l.or    r3,r0,r25
         LOAD_SYMBOL_2_GPR(r24, or32_early_setup)
         l.jalr r24
          l.nop
diff --git a/arch/openrisc/kernel/setup.c b/arch/openrisc/kernel/setup.c
index 1422f747f52b..bf5eba22ce9e 100644
--- a/arch/openrisc/kernel/setup.c
+++ b/arch/openrisc/kernel/setup.c
@@ -207,18 +207,18 @@ void __init setup_cpuinfo(void)
  * Handles the pointer to the device tree that this kernel is to use
  * for establishing the available platform devices.
  *
- * For now, this is limited to using the built-in device tree.  In the future,
- * it is intended that this function will take a pointer to the device tree
- * that is potentially built-in, but potentially also passed in by the
- * bootloader, or discovered by some equally clever means...
+ * Falls back on built-in device tree in case null pointer is passed.
  */
 
-void __init or32_early_setup(void)
+void __init or32_early_setup(unsigned int fdt)
 {
-
-        early_init_devtree(__dtb_start);
-
-        printk(KERN_INFO "Compiled-in FDT at 0x%p\n", __dtb_start);
+        if (fdt) {
+                early_init_devtree((void*) fdt);
+                printk(KERN_INFO "FDT at 0x%08x\n", fdt);
+        } else {
+                early_init_devtree(__dtb_start);
+                printk(KERN_INFO "Compiled-in FDT at %p\n", __dtb_start);
+        }
 }
 
 static int __init openrisc_device_probe(void)