[PATCH 01/15] Make bootm optionally use pre-existing atags for Linux kernel boot.

[Alistair Buxton]

This patch adapts the bootm command so that it can use an existing atags command
set up by a previous bootloader. If the environment variable "atags" is unset,
bootm behaves as normal. If "atags" is set, bootm will skip all boot args setup
entirely, and pass the address found in "atags". For example, if a previous boot
loader already set up the atags struct at 0x80000100:

setenv atags 0x80000100; bootm 0x80008000

Signed-off-by: Alistair Buxton <a.j.buxton at gmail.com>
---
 arch/arm/lib/bootm.c |   37 ++++++++++++++++++++++++++++---------
 1 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/arch/arm/lib/bootm.c b/arch/arm/lib/bootm.c
index 802e833..262efda 100644
--- a/arch/arm/lib/bootm.c
+++ b/arch/arm/lib/bootm.c
@@ -100,6 +100,13 @@ int do_bootm_linux(int flag, int argc, char *argv[], bootm_headers_t *images)
 	int	machid = bd->bi_arch_number;
 	void	(*kernel_entry)(int zero, int arch, uint params);
 
+#ifdef CONFIG_CHAINLOADER
+	uint	params;
+	#define PARAMS params
+#else
+	#define PARAMS (bd->bi_boot_params)
+#endif
+
 #ifdef CONFIG_CMDLINE_TAG
 	char *commandline = getenv ("bootargs");
 #endif
@@ -125,34 +132,46 @@ int do_bootm_linux(int flag, int argc, char *argv[], bootm_headers_t *images)
 	debug ("## Transferring control to Linux (at address %08lx) ...\n",
 	       (ulong) kernel_entry);
 
+#ifdef CONFIG_CHAINLOADER
+	s = getenv ("atags");
+	if (s) {
+		params = simple_strtoul (s, NULL, 16);
+		printf ("Using existing atags at 0x%x\n", params);
+	} else {
+#endif
+
 #if defined (CONFIG_SETUP_MEMORY_TAGS) || \
     defined (CONFIG_CMDLINE_TAG) || \
     defined (CONFIG_INITRD_TAG) || \
     defined (CONFIG_SERIAL_TAG) || \
     defined (CONFIG_REVISION_TAG)
-	setup_start_tag (bd);
+		setup_start_tag (bd);
 #ifdef CONFIG_SERIAL_TAG
-	setup_serial_tag (&params);
+		setup_serial_tag (&params);
 #endif
 #ifdef CONFIG_REVISION_TAG
-	setup_revision_tag (&params);
+		setup_revision_tag (&params);
 #endif
 #ifdef CONFIG_SETUP_MEMORY_TAGS
-	setup_memory_tags (bd);
+		setup_memory_tags (bd);
 #endif
 #ifdef CONFIG_CMDLINE_TAG
-	setup_commandline_tag (bd, commandline);
+		setup_commandline_tag (bd, commandline);
 #endif
 #ifdef CONFIG_INITRD_TAG
-	if (images->rd_start && images->rd_end)
-		setup_initrd_tag (bd, images->rd_start, images->rd_end);
+		if (images->rd_start && images->rd_end)
+			setup_initrd_tag (bd, images->rd_start, images->rd_end);
+#endif
+		setup_end_tag(bd);
 #endif
-	setup_end_tag(bd);
+
+#ifdef CONFIG_CHAINLOADER
+	}
 #endif
 
 	announce_and_cleanup();
 
-	kernel_entry(0, machid, bd->bi_boot_params);
+	kernel_entry(0, machid, PARAMS);
 	/* does not return */
 
 	return 1;
-- 
1.7.4.1


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