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[PULL 04/12] RISC-V: Place DTB at 3GB boundary instead of 4GB

From: Alistair Francis
Subject: [PULL 04/12] RISC-V: Place DTB at 3GB boundary instead of 4GB
Date: Sun, 17 Jan 2021 13:53:55 -0800

From: Atish Patra <atish.patra@wdc.com>

Currently, we place the DTB at 2MB from 4GB or end of DRAM which ever is
lesser. However, Linux kernel can address only 1GB of memory for RV32.
Thus, it can not map anything beyond 3GB (assuming 2GB is the starting address).
As a result, it can not process DT and panic if opensbi dynamic firmware
is used. While at it, place the DTB further away to avoid in memory placement
issues in future.

Fix this by placing the DTB at 16MB from 3GB or end of DRAM whichever is lower.

Fixes: 66b1205bc5ab ("RISC-V: Copy the fdt in dram instead of ROM")

Reviewed-by: Bin Meng <bin.meng@windriver.com>
Tested-by: Bin Meng <bin.meng@windriver.com>
Signed-off-by: Atish Patra <atish.patra@wdc.com>
Message-id: 20210107091127.3407870-1-atish.patra@wdc.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
 hw/riscv/boot.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/hw/riscv/boot.c b/hw/riscv/boot.c
index 83586aef41..10a601b4dc 100644
--- a/hw/riscv/boot.c
+++ b/hw/riscv/boot.c
@@ -194,11 +194,11 @@ uint32_t riscv_load_fdt(hwaddr dram_base, uint64_t 
mem_size, void *fdt)
      * We should put fdt as far as possible to avoid kernel/initrd overwriting
      * its content. But it should be addressable by 32 bit system as well.
-     * Thus, put it at an aligned address that less than fdt size from end of
-     * dram or 4GB whichever is lesser.
+     * Thus, put it at an 16MB aligned address that less than fdt size from the
+     * end of dram or 3GB whichever is lesser.
-    temp = MIN(dram_end, 4096 * MiB);
-    fdt_addr = QEMU_ALIGN_DOWN(temp - fdtsize, 2 * MiB);
+    temp = MIN(dram_end, 3072 * MiB);
+    fdt_addr = QEMU_ALIGN_DOWN(temp - fdtsize, 16 * MiB);
     /* copy in the device tree */

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