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From: Jiaxun Yang <jiaxun.yang@flygoat.com>
Date: Wed, 22 May 2024 23:02:17 +0100
Subject: [PATCH v3 1/4] LoongArch: Fix built-in DTB detection
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Message-Id: <20240522-loongarch-booting-fixes-v3-1-25e77a8fc86e@flygoat.com>
References: <20240522-loongarch-booting-fixes-v3-0-25e77a8fc86e@flygoat.com>
In-Reply-To: <20240522-loongarch-booting-fixes-v3-0-25e77a8fc86e@flygoat.com>
To: Huacai Chen <chenhuacai@kernel.org>, 
 Binbin Zhou <zhoubinbin@loongson.cn>
Cc: loongarch@lists.linux.dev, linux-kernel@vger.kernel.org, 
 Jiaxun Yang <jiaxun.yang@flygoat.com>, stable@vger.kernel.org

fdt_check_header(__dtb_start) will always success because kernel
provided a dummy dtb, and by coincidence __dtb_start clashed with
entry of this dummy dtb. The consequence is fdt passed from
firmware will never be taken.

Fix by trying to utilise __dtb_start only when CONFIG_BUILTIN_DTB
is enabled.

Cc: stable@vger.kernel.org
Fixes: 7b937cc243e5 ("of: Create of_root if no dtb provided by firmware")
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
---
v3: Better reasoning in commit message, thanks Binbin and Huacai!
---
 arch/loongarch/kernel/setup.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
index 60e0fe97f61a..ea6d5db6c878 100644
--- a/arch/loongarch/kernel/setup.c
+++ b/arch/loongarch/kernel/setup.c
@@ -275,16 +275,18 @@ static void __init arch_reserve_crashkernel(void)
 static void __init fdt_setup(void)
 {
 #ifdef CONFIG_OF_EARLY_FLATTREE
-	void *fdt_pointer;
+	void *fdt_pointer = NULL;
 
 	/* ACPI-based systems do not require parsing fdt */
 	if (acpi_os_get_root_pointer())
 		return;
 
+#ifdef CONFIG_BUILTIN_DTB
 	/* Prefer to use built-in dtb, checking its legality first. */
 	if (!fdt_check_header(__dtb_start))
 		fdt_pointer = __dtb_start;
-	else
+#endif
+	if (!fdt_pointer)
 		fdt_pointer = efi_fdt_pointer(); /* Fallback to firmware dtb */
 
 	if (!fdt_pointer || fdt_check_header(fdt_pointer))

-- 
2.43.0