rpi: passthrough of the firmware provided FDT blob
Raspberry firmware used to pass a FDT blob at a fixed address (0x100),
but this is not true anymore. The address now depends on both the
memory size and the blob size [1].
If one wants to passthrough this FDT blob to the kernel, the most
reliable way is to save its address from the r2/x0 register in the
U-Boot entry point and expose it in a environment variable for
further processing.
This patch just does this:
- save the provided address in the global variable fw_dtb_pointer
- expose it in ${fdt_addr} if it points to a a valid FDT blob
There are many different ways to use it. One can, for example, use
the following script which will extract from the tree the command
line built by the firmware, then hand over the blob to a previously
loaded kernel:
fdt addr ${fdt_addr}
fdt get value bootargs /chosen bootargs
bootz ${kernel_addr_r} - ${fdt_addr}
Alternatively, users relying on sysboot/pxe can simply omit any FDT
statement in their extlinux.conf file, U-Boot will automagically pick
${fdt_addr} and pass it to the kernel.
[1] https://www.raspberrypi.org/forums//viewtopic.php?f=107&t=134018
Signed-off-by: Cédric Schieli <cschieli@gmail.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
diff --git a/board/raspberrypi/rpi/rpi.c b/board/raspberrypi/rpi/rpi.c
index 6245b36..ffd6d31 100644
--- a/board/raspberrypi/rpi/rpi.c
+++ b/board/raspberrypi/rpi/rpi.c
@@ -25,6 +25,9 @@
DECLARE_GLOBAL_DATA_PTR;
+/* From lowlevel_init.S */
+extern unsigned long fw_dtb_pointer;
+
static const struct bcm2835_gpio_platdata gpio_platdata = {
.base = BCM2835_GPIO_BASE,
};
@@ -285,6 +288,31 @@
setenv("fdtfile", fdtfile);
}
+/*
+ * If the firmware provided a valid FDT at boot time, let's expose it in
+ * ${fdt_addr} so it may be passed unmodified to the kernel.
+ */
+static void set_fdt_addr(void)
+{
+ if (getenv("fdt_addr"))
+ return;
+
+ if (fdt_magic(fw_dtb_pointer) != FDT_MAGIC)
+ return;
+
+ setenv_hex("fdt_addr", fw_dtb_pointer);
+}
+
+/*
+ * Prevent relocation from stomping on a firmware provided FDT blob.
+ */
+unsigned long board_get_usable_ram_top(unsigned long total_size)
+{
+ if ((gd->ram_top - fw_dtb_pointer) > SZ_64M)
+ return gd->ram_top;
+ return fw_dtb_pointer & ~0xffff;
+}
+
static void set_usbethaddr(void)
{
ALLOC_CACHE_ALIGN_BUFFER(struct msg_get_mac_address, msg, 1);
@@ -356,6 +384,7 @@
int misc_init_r(void)
{
+ set_fdt_addr();
set_fdtfile();
set_usbethaddr();
#ifdef CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG