On 11/08/2016 04:50 AM, Jonathan Liu wrote:
On 8 November 2016 at 14:14, Stephen Warren swarren@wwwdotorg.org wrote:
On 11/07/2016 07:44 AM, Cédric Schieli wrote:
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
diff --git a/board/raspberrypi/rpi/rpi.c b/board/raspberrypi/rpi/rpi.c
+#ifdef CONFIG_ARM64 +void save_boot_params(unsigned long dtb) +#else +void save_boot_params(unsigned long r0, unsigned long r1, unsigned long dtb) +#endif +{
fw_dtb_pointer = dtb;save_boot_params_ret();+}
I think you need to write that function in assembly. This "function" is called very early during U-Boot startup, before any stack pointer is set up. You can't guarantee that a function written in C won't attempt to use the stack, although admittedly with the current code, Makefile, and the Ubuntu compilers, it just happens not to.
Apparently tegra also uses a C function for save_boot_params in arch/arm/mach-tegra/board.c...
Yes, that should be fixed. Simon, can you please look into that? I'm not sure whether the function is even needed; perhaps best to simply delete it.
The comment in arch/arm/include/asm/system.h suggests that save_boot_params() can be written in C: /**
- save_boot_params_ret() - Return from save_boot_params()
- If you provide save_boot_params(), then you should jump back to this
- function when done. Try to preserve all registers.
- If your implementation of save_boot_params() is in C then it is acceptable
That should be fixed too; writing the function in C isn't guaranteed to work.
- to simply call save_boot_params_ret() at the end of your function. Since
- there is no link register set up, you cannot just exit the function. U-Boot
- will return to the (initialised) value of lr, and likely crash/hang.
- If your implementation of save_boot_params() is in assembler then you
- should use 'b' or 'bx' to return to save_boot_params_ret.
*/ void save_boot_params_ret(void);
As mentioned in the commit that added it: commit 5519912164698b634893913b4408fee736d01d06 Author: Simon Glass sjg@chromium.org Date: Mon May 4 11:31:03 2015 -0600
arm: Add a prototype for save_boot_params_ret() It is convenient for some boards to implement save_boot_params() in C rather than assembler. Provide a way to return in this case. Signed-off-by: Simon Glass <sjg@chromium.org> Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>Aside from that issue, this version looks fine.
Regards, Jonathan