[PATCH v2] qemu-arm: round down memory to multiple of 2MB for LPAE

[Igor Opaniuk]

QEMU's -m option can take fractional megabyte values,
and lowest granularity seems to be 0x2000.
For example, run qemu with amount of memory set to 100005k (0x61A9400):

$ qemu-system-arm -machine virt -cpu cortex-a15 -m 100005k \
-bios denx/u-boot.bin -nographic

=> fdt addr $fdt_addr
=> fdt print /memory at 40000000
memory at 40000000 {
        reg = <0x00000000 0x40000000 0x00000000 0x061aa000>;
        device_type = "memory";
};

When LPAE is enabled, 1:1 mapping is created using 2 MB blocks.
In case amount of memory provided to QEMU is not multiple
of 2 MB, hang occurs during MMU initialization.

How to reproduce:
qemu-system-arm -machine virt -m 1058 -nographic -bios u-boot.bin - boots
qemu-system-arm -machine virt -m 1057 -nographic -bios u-boot.bin - hangs

DRAM:  1 GiB
initcall: 60011df8
initcall: 60011904
New Stack Pointer is: 80fffe90
initcall: 60011a20
initcall: 60011bcc
initcall: 60011bd4
initcall: 600119b4
Relocation Offset is: 22042000
Relocating to 82042000, new gd at 81001ed0, sp at 80fffe90
initcall: 60011b8c
initcall: 82053ea0
initcall: 82053ea8
initcall: 60012040 (relocated to 82054040)
dram_bank_mmu_setup: bank: 0
- hang here during mmu init -

This patches rounds down to the nearest multiple of 2MB when
CONFIG_ARMV7_LPAE=y.

Fixes: 3fa914af82("arm: qemu: implement enable_caches()")
Signed-off-by: Igor Opaniuk <igor.opaniuk at foundries.io>
---

Changes in v2:
- Adjust commit message, add more details

 board/emulation/qemu-arm/qemu-arm.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/board/emulation/qemu-arm/qemu-arm.c b/board/emulation/qemu-arm/qemu-arm.c
index 942f1fff571..ecfd19f1a7e 100644
--- a/board/emulation/qemu-arm/qemu-arm.c
+++ b/board/emulation/qemu-arm/qemu-arm.c
@@ -127,6 +127,18 @@ int dram_init(void)
 	if (fdtdec_setup_mem_size_base() != 0)
 		return -EINVAL;
 
+	/*
+	 * When LPAE is enabled (ARMv7),
+	 * 1:1 mapping is created using 2 MB blocks.
+	 *
+	 * In case amount of memory provided to QEMU
+	 * is not multiple of 2 MB, round down the amount
+	 * of available memory to avoid hang during MMU
+	 * initialization.
+	 */
+	if (CONFIG_IS_ENABLED(ARMV7_LPAE))
+		gd->ram_size -= (gd->ram_size % 0x200000);
+
 	return 0;
 }
 
-- 
2.34.1