Merging code with arch condition into head.S

[Ard Biesheuvel]

On 18 August 2016 at 12:35, Rafał Miłecki <zajec5 at gmail.com> wrote:
> Hi,
>
> I'd like to ask for help with writing my arcm/arm/boot/compressed/head-foo.S.
>
> There is probably a bug in bootloader on *a lot* market-available
> devices that needs a very early fix executed during decompression. If
> we don't implement it, Broadcom Northstar devices hang in 25% of tries
> and BCM53573 devices don't boot at all.
>

Could you elaborate on the nature of the fix?

> The problem is ARCH_BCM_5301X is used with ARCH_MULTI_V7, so we really
> shouldn't merge some extra code into head.S and execute it
> unconditionally. I'd like to ask if you can suggest some idea for a
> sane architecture check.
>
> Ideally I'd read it from DT, but I don't think I can read machine
> "compatible" from ASM. As alternative I could try reading SoC chip ID
> from ChipCommon component which Broadcom always maps at 0x18000000.
> Would that be safe enough? Could reading from such offset do any harm
> on other devices?
>

Yes.

> Maybe you have some better ideas?
>
> I was looking for similar solutions in the kernel, but I found none.
> There are e.g. head-sa1100.S and head-sharpsl.S but they seem to be
> used on architectures that don't use ARCH_MULTI_V7.
>

Generally, it is not the kernel's job to fix broken bootloaders,
especially not in generic kernels. What kind of bootloader does this
bug exist in?

-- 
Ard.