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, 25 insertions, 5 deletions

diff --git a/hw/riscv/boot.c b/hw/riscv/boot.c
index 2d03a9a..2e53494 100644
--- a/hw/riscv/boot.c
+++ b/hw/riscv/boot.c
@@ -249,9 +249,21 @@ void riscv_load_initrd(MachineState *machine, uint64_t kernel_entry)
     }
 }
 
-uint64_t riscv_load_fdt(hwaddr dram_base, uint64_t mem_size, void *fdt)
+/*
+ * The FDT should be put at the farthest point possible to
+ * avoid overwriting it with the kernel/initrd.
+ *
+ * This function makes an assumption that the DRAM is
+ * contiguous. It also cares about 32-bit systems and
+ * will limit fdt_addr to be addressable by them even for
+ * 64-bit CPUs.
+ *
+ * The FDT is fdt_packed() during the calculation.
+ */
+uint64_t riscv_compute_fdt_addr(hwaddr dram_base, uint64_t mem_size,
+                                void *fdt)
 {
-    uint64_t temp, fdt_addr;
+    uint64_t temp;
     hwaddr dram_end = dram_base + mem_size;
     int ret = fdt_pack(fdt);
     int fdtsize;
@@ -272,7 +284,17 @@ uint64_t riscv_load_fdt(hwaddr dram_base, uint64_t mem_size, void *fdt)
      * end of dram or 3GB whichever is lesser.
      */
     temp = (dram_base < 3072 * MiB) ? MIN(dram_end, 3072 * MiB) : dram_end;
-    fdt_addr = QEMU_ALIGN_DOWN(temp - fdtsize, 2 * MiB);
+
+    return QEMU_ALIGN_DOWN(temp - fdtsize, 2 * MiB);
+}
+
+/*
+ * 'fdt_addr' is received as hwaddr because boards might put
+ * the FDT beyond 32-bit addressing boundary.
+ */
+void riscv_load_fdt(hwaddr fdt_addr, void *fdt)
+{
+    uint32_t fdtsize = fdt_totalsize(fdt);
 
     /* copy in the device tree */
     qemu_fdt_dumpdtb(fdt, fdtsize);
@@ -281,8 +303,6 @@ uint64_t riscv_load_fdt(hwaddr dram_base, uint64_t mem_size, void *fdt)
                           &address_space_memory);
     qemu_register_reset_nosnapshotload(qemu_fdt_randomize_seeds,
                         rom_ptr_for_as(&address_space_memory, fdt_addr, fdtsize));
-
-    return fdt_addr;
 }
 
 void riscv_rom_copy_firmware_info(MachineState *machine, hwaddr rom_base,