um: Add devicetree support

Add a dtb=<filename> option to boot UML with a devicetree blob.  This
can be used for testing driver code using UML.

Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
[rw: Add dependency on CONFIG_OF]
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/Kconfig

@@ -18,6 +18,7 @@ config UML
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DEBUG_BUGVERBOSE
 	select NO_DMA if !UML_DMA_EMULATION
+	select OF_EARLY_FLATTREE if OF
 	select GENERIC_IRQ_SHOW
 	select GENERIC_CPU_DEVICES
 	select HAVE_GCC_PLUGINS

arch/um/kernel/Makefile

@@ -22,6 +22,7 @@ obj-y += load_file.o
 
 obj-$(CONFIG_BLK_DEV_INITRD) += initrd.o
 obj-$(CONFIG_GPROF)	+= gprof_syms.o
+obj-$(CONFIG_OF) += dtb.o
 obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
 obj-$(CONFIG_STACKTRACE) += stacktrace.o
 obj-$(CONFIG_GENERIC_PCI_IOMAP) += ioport.o

arch/um/kernel/dtb.c

@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/init.h>
+#include <linux/of_fdt.h>
+#include <linux/printk.h>
+#include <linux/memblock.h>
+#include <init.h>
+
+#include "um_arch.h"
+
+static char *dtb __initdata;
+
+void uml_dtb_init(void)
+{
+	long long size;
+	void *area;
+
+	area = uml_load_file(dtb, &size);
+	if (!area)
+		return;
+
+	if (!early_init_dt_scan(area)) {
+		pr_err("invalid DTB %s\n", dtb);
+		memblock_free(area, size);
+		return;
+	}
+
+	unflatten_device_tree();
+	early_init_fdt_scan_reserved_mem();
+}
+
+static int __init uml_dtb_setup(char *line, int *add)
+{
+	dtb = line;
+	return 0;
+}
+
+__uml_setup("dtb=", uml_dtb_setup,
+"dtb=<file>\n"
+"    Boot the kernel with the devicetree blob from the specified file.\n"
+);

arch/um/kernel/um_arch.c

@@ -29,6 +29,8 @@
 #include <mem_user.h>
 #include <os.h>
 
+#include "um_arch.h"
+
 #define DEFAULT_COMMAND_LINE_ROOT "root=98:0"
 #define DEFAULT_COMMAND_LINE_CONSOLE "console=tty"
 
@@ -407,6 +409,7 @@ void __init setup_arch(char **cmdline_p)
 	stack_protections((unsigned long) &init_thread_info);
 	setup_physmem(uml_physmem, uml_reserved, physmem_size, highmem);
 	mem_total_pages(physmem_size, iomem_size, highmem);
+	uml_dtb_init();
 	read_initrd();
 
 	paging_init();

arch/um/kernel/um_arch.h

@@ -5,4 +5,10 @@
 
 extern void * __init uml_load_file(const char *filename, unsigned long long *size);
 
+#ifdef CONFIG_OF
+extern void __init uml_dtb_init(void);
+#else
+static inline void uml_dtb_init(void) { }
+#endif
+
 #endif