From 781d7cd4c3364e9d38fa12a342c5ad4c7e33a5ba Mon Sep 17 00:00:00 2001
From: Christian Marangi <ansuelsmth@gmail.com>
Date: Fri, 19 Jan 2024 20:33:10 +0100
Subject: [PATCH v2 2/2] ARM: decompressor: add option to ignore MEM ATAGs

Some bootloaders can pass broken MEM ATAGs that provide hardcoded
information about mounted RAM size and physical location.
Example booloader provide RAM of size 1.7Gb but actual mounted RAM
size is 512Mb causing kernel panic.

Add option CONFIG_ARM_ATAG_DTB_COMPAT_IGNORE_MEM to ignore these ATAG
and not augument appended DTB memory node.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
---
 arch/arm/Kconfig                        | 12 ++++++++++++
 arch/arm/boot/compressed/atags_to_fdt.c |  4 ++++
 2 files changed, 16 insertions(+)

--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1549,6 +1549,18 @@ config ARM_ATAG_DTB_COMPAT
 	  bootloaders, this option allows zImage to extract the information
 	  from the ATAG list and store it at run time into the appended DTB.
 
+config ARM_ATAG_DTB_COMPAT_IGNORE_MEM
+	bool "Ignore MEM ATAG information from bootloader"
+	depends on ARM_ATAG_DTB_COMPAT
+	help
+	  Some bootloaders can pass broken MEM ATAGs that provide hardcoded
+	  information about mounted RAM size and physical location.
+	  Example booloader provide RAM of size 1.7Gb but actual mounted RAM
+	  size is 512Mb causing kernel panic.
+
+	  Enable this option if MEM ATAGs should be ignored and the memory
+	  node in the appended DTB should NOT be augumented.
+
 choice
 	prompt "Kernel command line type" if ARM_ATAG_DTB_COMPAT
 	default ARM_ATAG_DTB_COMPAT_CMDLINE_FROM_BOOTLOADER
--- a/arch/arm/boot/compressed/atags_to_fdt.c
+++ b/arch/arm/boot/compressed/atags_to_fdt.c
@@ -170,6 +170,10 @@ int atags_to_fdt(void *atag_list, void *
 				setprop_string(fdt, "/chosen", "bootargs",
 					       atag->u.cmdline.cmdline);
 		} else if (atag->hdr.tag == ATAG_MEM) {
+			/* Bootloader MEM ATAG are broken and should be ignored */
+			if (IS_ENABLED(CONFIG_ARM_ATAG_DTB_COMPAT_IGNORE_MEM))
+				continue;
+
 			if (memcount >= sizeof(mem_reg_property)/4)
 				continue;
 			if (!atag->u.mem.size)
