hw/riscv: split fdt address calculation from fdt load

A common trend in other archs is to calculate the fdt address, which is
usually straightforward, and then calling a function that loads the
fdt/dtb by using that address.

riscv_load_fdt() is doing a bit too much in comparison. It's calculating
the fdt address via an elaborated heuristic to put the FDT at the bottom
of DRAM, and "bottom of DRAM" will vary across boards and
configurations, then it's actually loading the fdt, and finally it's
returning the fdt address used to the caller.

Reduce the existing complexity of riscv_load_fdt() by splitting its code
into a new function, riscv_compute_fdt_addr(), that will take care of
all fdt address logic. riscv_load_fdt() can then be a simple function
that just loads a fdt at the given fdt address.

We're also taken the opportunity to clarify the intentions and
assumptions made by these functions. riscv_load_fdt() is now receiving a
hwaddr as fdt_addr because there is no restriction of having to load the
fdt in higher addresses that doesn't fit in an uint32_t.

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-Id: <20230201171212.1219375-3-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/hw/riscv/sifive_u.c b/hw/riscv/sifive_u.c
index 2fb6ee2..626d4dc 100644
--- a/hw/riscv/sifive_u.c
+++ b/hw/riscv/sifive_u.c
@@ -616,9 +616,10 @@ static void sifive_u_machine_init(MachineState *machine)
         kernel_entry = 0;
     }
 
-    /* Compute the fdt load address in dram */
-    fdt_load_addr = riscv_load_fdt(memmap[SIFIVE_U_DEV_DRAM].base,
-                                   machine->ram_size, machine->fdt);
+    fdt_load_addr = riscv_compute_fdt_addr(memmap[SIFIVE_U_DEV_DRAM].base,
+                                           machine->ram_size, machine->fdt);
+    riscv_load_fdt(fdt_load_addr, machine->fdt);
+
     if (!riscv_is_32bit(&s->soc.u_cpus)) {
         start_addr_hi32 = (uint64_t)start_addr >> 32;
     }