[U-Boot] [PATCH] armv8: aarch64: Fix the warning about x1-x3 nonzero issue

[Alexander Graf]

On 01/13/2017 09:23 AM, Alison Wang wrote:
>>> Am 13.01.2017 um 08:50 schrieb Alison Wang <b18965 at freescale.com>:
>>>
>>> For 64-bit kernel, there is a warning about x1-x3 nonzero in
>> violation
>>> of boot protocol. x3 should be reset to zero before jumping to the
>>> kernel.
>>>
>>> This patch will adjust the parameters to transfer and make sure x3 is
>>> zero.
>>>
>>> Signed-off-by: Alison Wang <alison.wang at nxp.com>
>> If x3 is part of the boot protocol, please treat it as function
>> argument rather than hard code it to 0.
>>
> [Alison Wang] I think x3 need to set to 0. Refer to the codes for the warning in kernel,
>
>          if (boot_args[1] || boot_args[2] || boot_args[3]) {
>                  pr_err("WARNING: x1-x3 nonzero in violation of boot protocol:\n"
>                          "\tx1: %016llx\n\tx2: %016llx\n\tx3: %016llx\n"
>                          "This indicates a broken bootloader or old kernel\n",
>                          boot_args[1], boot_args[2], boot_args[3]);
>          }

Yes, that merely means that the kernel doesn't take 3 arguments, it 
takes 4. Today args[1..3] have to be 0, but I don't want to iron that 
out in u-boot code.

So in pseudo-code, what we do today is we call

   entry(dt_addr, 0, 0);

and instead we should be calling

   entry(dt_addr, 0, 0, 0);

So in U-Boot code that means we should change the prototype for our 
switch function from

void armv8_switch_to_el2(u64 args, u64 mach_nr, u64 fdt_addr,
                          u64 entry_point, u64 es_flag);

to

void armv8_switch_to_el2(u64 args, u64 mach_nr, u64 fdt_addr,
                          u64 arg4, u64 entry_point, u64 es_flag);

and adapt the macros accordingly to use x5/x6 instead of x4/5.


Alex