[PATCH 1/2] powerpc/prom: fix /chosen properties read from wrong node

[Sang-Heon Jeon <ekffu200098@gmail.com>]

Commit 60f20d84dc81 ("of/fdt: Rework early_init_dt_scan_chosen() to
call directly") changed early_init_dt_scan_chosen() to be called
directly instead of via of_scan_flat_dt(). After this change,
early_init_dt_scan_chosen_ppc() does not behave as intended in either
case below:

- /chosen(or /chosen@0) exists: early_init_dt_scan_chosen() always 
  succeeds, so early_init_dt_scan_chosen_ppc() then reads properties
  from the root node (first iteration) instead of chosen node.

- /chosen does not exist:
  - Until commit 064e32dc5b03 ("of: fdt: Honor CONFIG_CMDLINE* even without
    /chosen node, take 2"), early_init_dt_scan_chosen() returns -ENOENT
    and early_init_dt_scan_chosen_ppc() returns 0. So of_scan_flat_dt()
    iterates over all remaining nodes. Not a bug but unnecessary.
  - After above commit, early_init_dt_scan_chosen() returns 0 and
    early_init_dt_scan_chosen_ppc() returns 1. So it reads properties
    from the root node (first iteration) instead of chosen node, same as
    the chosen node exist case above.

Instead of using of_scan_flat_dt() for chosen node handling, first call
early_init_dt_scan_chosen() directly to handle common chosen node
properties. Then call early_init_dt_scan_chosen_ppc(), which is updated
to handle powerpc-specific chosen node properties.

Both now look up chosen node directly to avoid reading from the wrong node.

Fixes: 60f20d84dc81 ("of/fdt: Rework early_init_dt_scan_chosen() to call directly")
Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
---
QEMU-based test results

$ fdtput -t bx chosen.dtb /chosen linux,crashkernel-base 00 00 00 10 00 00 00 00
$ fdtput -t bx chosen.dtb /chosen linux,crashkernel-size 00 00 00 02 00 00 00 00
$ qemu-system-ppc64 -M powernv9,dtb=chosen.dtb ...

1) AS-IS (before fix)
# cat /sys/kernel/kexec_crash_size
0

2) TO-BE (after fix)
# cat /sys/kernel/kexec_crash_size
33554432

---
 arch/powerpc/kernel/prom.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 9ed9dde7d231..34318ddb4a73 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -450,15 +450,17 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
 	return 0;
 }
 
-static int __init early_init_dt_scan_chosen_ppc(unsigned long node,
-						const char *uname,
-						int depth, void *data)
+static void __init early_init_dt_scan_chosen_ppc(void)
 {
+	const void *fdt = initial_boot_params;
 	const unsigned long *lprop; /* All these set by kernel, so no need to convert endian */
+	int node;
 
-	/* Use common scan routine to determine if this is the chosen node */
-	if (early_init_dt_scan_chosen(data) < 0)
-		return 0;
+	node = fdt_path_offset(fdt, "/chosen");
+	if (node < 0)
+		node = fdt_path_offset(fdt, "/chosen@0");
+	if (node < 0)
+		return;
 
 #ifdef CONFIG_PPC64
 	/* check if iommu is forced on or off */
@@ -491,9 +493,6 @@ static int __init early_init_dt_scan_chosen_ppc(unsigned long node,
 	if (lprop)
 		crashk_res.end = crashk_res.start + *lprop - 1;
 #endif
-
-	/* break now */
-	return 1;
 }
 
 /*
@@ -818,7 +817,8 @@ void __init early_init_devtree(void *params)
 	 * device-tree, including the platform type, initrd location and
 	 * size, TCE reserve, and more ...
 	 */
-	of_scan_flat_dt(early_init_dt_scan_chosen_ppc, boot_command_line);
+	early_init_dt_scan_chosen(boot_command_line);
+	early_init_dt_scan_chosen_ppc();
 
 	/* Append additional parameters passed for fadump capture kernel */
 	fadump_append_bootargs();
-- 
2.43.0