[PATCH] ARM: xip: disable PATCH_PHYS_VIRT for ARCH_MULTIPLATFORM when XIP

[Geert Uytterhoeven]

Hi Russell,

On Wed, Feb 8, 2017 at 6:44 PM, Russell King - ARM Linux
<linux at armlinux.org.uk> wrote:
> On Wed, Feb 08, 2017 at 12:22:09PM -0500, Chris Brandt wrote:
>> Since ARCH_MULTIPLATFORM explicitly selects ARM_PATCH_PHYS_VIRT, even
>> though ARCH_MULTIPLATFORM has 'depends on !XIP_KERNEL', ARM_PATCH_PHYS_VIRT
>> is still forcibly selected. The result is that PHYS_OFFSET depends on
>> !ARM_PATCH_PHYS_VIRT. This means you cannot enter a physical RAM address
>> for an XIP kernel and you cannot build.
>>
>> Given that it is already clear in the Kconfig that ARM_PATCH_PHYS_VIRT and
>> XIP_KERNEL do not go well together (read the help for ARM_PATCH_PHYS_VIRT),
>> adding this condition to ARCH_MULTIPLATFORM is logical and will fix this
>> build issue.
>
> And, ergo, multiplatform kernels and XIP_KERNEL don't go together either.
> Think about it...
>
> This is why I regard those who want multiplatform to work with options
> such as XIP_KERNEL and NOMMU to be insane.
>
> Please, can we stop trying to make multiplatform also cover the situations
> where only a single class of platforms works (iow, the old way we used to
> deal with platforms is the most sensible solution.)
>
> IMHO multiplatform was done right for multiplatform but at the expense of
> totally breaking stuff like XIP and noMMU.  We need to stop trying to
> bend multiplatform to cover XIP and noMMU, but instead restore the old
> way of handling this _along_ with multiplatform as an additional option.

The problem is that "multiplatform" may mean one of two things:
  1. Build a single kernel that can run on multiple platforms.
     This is tricky when enabling XIP and/or NOMMU, as the physical parameters
     must be compatible with all platforms. But building a kernel with the
     right parameters is the responsibility of the user.
     I.e. don't shoot yourself in the foot.
  2. Your platform uses the arch/arm multiplatform framework.

As everything is being migrated to 2, not allowing XIP and/or NOMMU on
"multiplatform" is IMHO an insane limitation.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds