[PATCH v2] platform: generic: Keep some empty space in FDT passed to next stage

From: Anup Patel <apatel@ventanamicro.com>
To: Atish Patra <atishp@rivosinc.com>
Cc: Andrew Jones <ajones@ventanamicro.com>,
	Anup Patel <anup@brainfault.org>,
	opensbi@lists.infradead.org, Anup Patel <apatel@ventanamicro.com>
Subject: [PATCH v2] platform: generic: Keep some empty space in FDT passed to next stage
Date: Mon,  1 Dec 2025 10:30:14 +0530	[thread overview]
Message-ID: <20251201050014.8788-1-apatel@ventanamicro.com> (raw)

Leaving no empty space in the FDT passed to the next booting stage
causes the following U-Boot crash on Ventana internal platforms:

Unhandled exception: Load access fault
EPC: 00000000fffa6372 RA: 00000000fffa7418 TVAL: 0001746174730068
EPC: 0000000080245372 RA: 0000000080246418 reloc adjusted

SP:  00000000fef38440 GP:  00000000fef40e60 TP:  0000000000000000
T0:  00000000fef40a70 T1:  000000000000ff00 T2:  0000000000000000
S0:  00000000fffc17a8 S1:  00000000fef38d40 A0:  7375746174730068
A1:  00000000fffc17a8 A2:  0000000000000010 A3:  0000000000000010
A4:  0000000000000000 A5:  00000000fffc17b8 A6:  0000000000ff0000
A7:  000000000000b100 S2:  0000000000000000 S3:  0000000000000001
S4:  00000000fef38d40 S5:  7375746174730068 S6:  0000000000000000
S7:  00000000fef4eef0 S8:  00000000fef4ef90 S9:  0000000000000000
S10: 0000000000000000 S11: 00000000fef4efc0 T3:  00000000fef40ea8
T4:  0000000000ff0000 T5:  00000000fef40a60 T6:  00000000fef40a6c

To address the above issue, keep some minimal empty space in the
FDT instead of no empty space.

Fixes: bbe9a23060e9 ("platform: generic: Pack the FDT after applying fixups")
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
---
Changes since v1:
- Add Kconfig option for amount of empty space in FDT with default
  value as 4KB
---
 platform/generic/Kconfig    | 5 +++++
 platform/generic/platform.c | 3 +++
 2 files changed, 8 insertions(+)

diff --git a/platform/generic/Kconfig b/platform/generic/Kconfig
index 25b8886b..b1808012 100644
--- a/platform/generic/Kconfig
+++ b/platform/generic/Kconfig
@@ -23,6 +23,11 @@ config PLATFORM_GENERIC_MINOR_VER
 	range 0 65535
 	default 1
 
+config PLATFORM_GENERIC_FDT_EMPTY_SPACE
+	int "Platform FDT empty space (KB)"
+	range 0 1024
+	default 4
+
 config PLATFORM_ALLWINNER_D1
 	bool "Allwinner D1 support"
 	depends on FDT_IRQCHIP_PLIC
diff --git a/platform/generic/platform.c b/platform/generic/platform.c
index e66f99fa..ddfc9e80 100644
--- a/platform/generic/platform.c
+++ b/platform/generic/platform.c
@@ -245,7 +245,10 @@ int generic_final_init(bool cold_boot)
 	fdt_fixups(fdt);
 	fdt_domain_fixup(fdt);
 
+	/* Minimize the empty space in FDT to 4KB */
 	fdt_pack(fdt);
+	fdt_open_into(fdt, fdt, fdt_totalsize(fdt) +
+		      CONFIG_PLATFORM_GENERIC_FDT_EMPTY_SPACE * 1024);
 
 	return 0;
 }
-- 
2.43.0


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