MIPS: kexec: Use prepare method from Generic for UHI platforms

Out-of-tree platforms may not be based on Generic as shown in customer
communication. Share the prepare method with all using UHI boot protocol,
and put into machine_kexec.c.

The benefit is that, when having kexec_args related problems, developers
will naturally look into machine_kexec.c, where "CONFIG_UHI_BOOT" will be
found, prompting them to add "select UHI_BOOT" to the platform Kconfig. It
would otherwise require a lot debugging or online searching to be aware
that the solution is in Generic code.

Tested-by: Rachel Mozes <rachel.mozes@intel.com>
Reported-by: Rachel Mozes <rachel.mozes@intel.com>
Signed-off-by: Dengcheng Zhu <dzhu@wavecomp.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/20569/
Cc: pburton@wavecomp.com
Cc: ralf@linux-mips.org
Cc: linux-mips@linux-mips.org

arch/mips/Kconfig

@@ -133,6 +133,7 @@ config MIPS_GENERIC
 	select USB_UHCI_BIG_ENDIAN_DESC if CPU_BIG_ENDIAN
 	select USB_UHCI_BIG_ENDIAN_MMIO if CPU_BIG_ENDIAN
 	select USE_OF
+	select UHI_BOOT
 	help
 	  Select this to build a kernel which aims to support multiple boards,
 	  generally using a flattened device tree passed from the bootloader
@@ -2899,6 +2900,9 @@ config USE_OF
 	select OF_EARLY_FLATTREE
 	select IRQ_DOMAIN
 
+config UHI_BOOT
+	bool
+
 config BUILTIN_DTB
 	bool
 

arch/mips/generic/Makefile

@@ -15,5 +15,4 @@ obj-y += proc.o
 obj-$(CONFIG_YAMON_DT_SHIM)		+= yamon-dt.o
 obj-$(CONFIG_LEGACY_BOARD_SEAD3)	+= board-sead3.o
 obj-$(CONFIG_LEGACY_BOARD_OCELOT)	+= board-ocelot.o
-obj-$(CONFIG_KEXEC)			+= kexec.o
 obj-$(CONFIG_VIRT_BOARD_RANCHU)		+= board-ranchu.o

arch/mips/generic/kexec.c

@@ -1,44 +0,0 @@
-/*
- * Copyright (C) 2016 Imagination Technologies
- * Author: Marcin Nowakowski <marcin.nowakowski@mips.com>
- *
- * This program is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License as published by the
- * Free Software Foundation; either version 2 of the License, or (at your
- * option) any later version.
- */
-
-#include <linux/kexec.h>
-#include <linux/libfdt.h>
-#include <linux/uaccess.h>
-
-static int generic_kexec_prepare(struct kimage *image)
-{
-	int i;
-
-	for (i = 0; i < image->nr_segments; i++) {
-		struct fdt_header fdt;
-
-		if (image->segment[i].memsz <= sizeof(fdt))
-			continue;
-
-		if (copy_from_user(&fdt, image->segment[i].buf, sizeof(fdt)))
-			continue;
-
-		if (fdt_check_header(&fdt))
-			continue;
-
-		kexec_args[0] = -2;
-		kexec_args[1] = (unsigned long)
-			phys_to_virt((unsigned long)image->segment[i].mem);
-		break;
-	}
-	return 0;
-}
-
-static int __init register_generic_kexec(void)
-{
-	_machine_kexec_prepare = generic_kexec_prepare;
-	return 0;
-}
-arch_initcall(register_generic_kexec);

arch/mips/kernel/machine_kexec.c

@@ -9,6 +9,7 @@
 #include <linux/kexec.h>
 #include <linux/mm.h>
 #include <linux/delay.h>
+#include <linux/libfdt.h>
 
 #include <asm/cacheflush.h>
 #include <asm/page.h>
@@ -28,7 +29,6 @@ atomic_t kexec_ready_to_reboot = ATOMIC_INIT(0);
 void (*_crash_smp_send_stop)(void) = NULL;
 #endif
 
-int (*_machine_kexec_prepare)(struct kimage *) = NULL;
 void (*_machine_kexec_shutdown)(void) = NULL;
 void (*_machine_crash_shutdown)(struct pt_regs *regs) = NULL;
 
@@ -52,6 +52,46 @@ static void kexec_image_info(const struct kimage *kimage)
 	}
 }
 
+#ifdef CONFIG_UHI_BOOT
+
+static int uhi_machine_kexec_prepare(struct kimage *kimage)
+{
+	int i;
+
+	/*
+	 * In case DTB file is not passed to the new kernel, a flat device
+	 * tree will be created by kexec tool. It holds modified command
+	 * line for the new kernel.
+	 */
+	for (i = 0; i < kimage->nr_segments; i++) {
+		struct fdt_header fdt;
+
+		if (kimage->segment[i].memsz <= sizeof(fdt))
+			continue;
+
+		if (copy_from_user(&fdt, kimage->segment[i].buf, sizeof(fdt)))
+			continue;
+
+		if (fdt_check_header(&fdt))
+			continue;
+
+		kexec_args[0] = -2;
+		kexec_args[1] = (unsigned long)
+			phys_to_virt((unsigned long)kimage->segment[i].mem);
+		break;
+	}
+
+	return 0;
+}
+
+int (*_machine_kexec_prepare)(struct kimage *) = uhi_machine_kexec_prepare;
+
+#else
+
+int (*_machine_kexec_prepare)(struct kimage *) = NULL;
+
+#endif /* CONFIG_UHI_BOOT */
+
 int
 machine_kexec_prepare(struct kimage *kimage)
 {