[PATCH 10/62] ARM: efm32: select AUTO_ZRELADDR

[Rob Herring]

On Fri, Mar 21, 2014 at 1:54 PM, Uwe Kleine-König
<u.kleine-koenig at pengutronix.de> wrote:
> Hello Arnd,
>
> On Fri, Mar 21, 2014 at 04:10:37PM +0100, Arnd Bergmann wrote:
>> On Friday 21 March 2014 15:32:24 Uwe Kleine-König wrote:
>> > On Thu, Mar 20, 2014 at 11:16:20PM +0100, Arnd Bergmann wrote:
>> > > On Thursday 20 March 2014 21:48:47 Uwe Kleine-König wrote:
>> > > >
>> > > > On Wed, Mar 19, 2014 at 08:29:07PM +0100, Arnd Bergmann wrote:
>> > > > > The efm32 platform does not provide a zreladdr-y line its Makefile.boot,
>> > > > > so we always have to use CONFIG_AUTO_ZRELADDR in order to successfully
>> > > > > build and link a zImage.
>> > > > I wonder why you need to AUTO_ZRELADDR (which is there to guess
>> > > > zreladdr) while efm32 doesn't have an MMU and so there is nothing to
>> > > > guess. So I think this patch fixes a build problem, but it's not a good
>> > > > change.
>> > >
>> > > It is required in order to build a compressed zImage file. You mentioned
>> > > before that your system does not have enough RAM to support this, but
>> > > the compile-time option exists, and there is no dependency on MMU support
>> > > for it, nor should there be.
>> > My objection isn't about having only little RAM. AUTO_ZRELADDR is about
>> > guessing the physical address corresponding to PAGE_OFFSET. But without
>> > an MMU there is nothing to guess. So I wonder if the better change would
>> > be to do:
>> >
>> >         #ifdef CONFIG_MMU
>> >         #ifdef CONFIG_AUTO_ZRELADDR
>> >                 ... guess zreladdress based on instruction pointer
>> >         #else
>> >                 ... use zreladdr from Makefile.boot
>> >         #endif
>> >         #else
>> >                 ... use zreladdr = PAGE_OFFSET
>> >         #endif
>> >
>>
>> I don't see a reason to change the existing logic, it works for
>> both MMU and NOMMU kernels, and you are talking about *three* instructions
>> here.
> it doesn't matter how many instructions are involved. The relevant
> difference is that with my approach you fix the problem for all no-MMU
> platforms, with yours you only fix efm32. (OK, I think there are not too
> many no-MMU platforms, but still.) An even easier implementation would
> be to add something like:
>
>         ifeq($(zreladdr-y)$(CONFIG_MMU),)
>         zreladdr-y := CONFIG_PAGE_OFFSET + CONFIG_TEXT_OFFSET
>         endif
>
> to arch/arm/boot/Makefile.
>
> But I don't care much, if you still want to make EFM32 select
> AUTO_ZRELADDR go ahead.

How about a kconfig fix:

bool "Auto calculation of the decompressed kernel image address" if MMU
default y if !MMU

Rob