Re: [PATCH v2] Re: Adding support for device tree and command line

[Daniel Gimpelevich <daniel@gimpelevich.san-francisco.ca.us>]

On Sun, 2016-05-29 at 12:53 +0200, Jonas Gorski wrote:
> Maybe a better solution here would be to create a new symbol
> fw_passed_dtb and let the code store a1 in there if a0 is -2, or
> __appended_dtb in case it is valid? Then we wouldn't need to special
> case APPENDED_DTB for any mach wanting to use it, and they can just
> check fw_passed_dtb.
> 
> something like:
> 
> arch/mips/kernel/head.S:
> ...
> 
> #ifdef CONFIG_USE_OF
>         li              t1, -2
>         beq             a0, t1, dtb_found
>         move            t0, a0
> 
> #ifdef CONFIG_MIPS_RAW_APPENDED_DTB
>         PTR_LA          t0, __appended_dtb
> 
> #ifdef CONFIG_CPU_BIG_ENDIAN
>         li              t1, 0xd00dfeed
> #else
>         li              t1, 0xedfe0dd0
> #endif
>         lw              t2, (t0)
>         bne             t1, t2, no_dtb_found
>          nop
> 
> #endif
> no_dtb_found:
>         li              t0, 0
> dtb_found:
>         LONG_S          t0, fw_passed_dtb
> #endif

That prefers the wrong DTB in case both are present. I propose this
instead:

#ifdef CONFIG_USE_OF
#ifdef CONFIG_MIPS_RAW_APPENDED_DTB
        PTR_LA          t0, __appended_dtb

#ifdef CONFIG_CPU_BIG_ENDIAN
        li              t1, 0xd00dfeed
#else
        li              t1, 0xedfe0dd0
#endif
        lw              t2, (t0)
        beq             t1, t2, dtb_found
         nop

#endif
        li              t1, -2
        beq             a0, t1, dtb_found
        move            t0, a1

no_dtb_found:
        li              t0, 0
dtb_found:
        LONG_S          t0, fw_passed_dtb
#endif