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

[Alison Wang]

> 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.
> 
[Alison Wang] I understand your meaning. Actually, I thought that method too. Well, my concern is that there are more changes. Not only armv8_switch_to_el2 and armv8_switch_to_el1, all the places calling them need to change too. It may cause more problems. With this concern, I choose a simple way to fix this issue before.


Best Regards,
Alison Wang