Re: [PATCH 3/6] arm: kconfig: don't select TWD with local timer for Armada 370/XP

[Matt Sealey <matt-sEEEE4iEDtaXzmuOJsdVMQ@public.gmane.org>]

On Mon, Jan 21, 2013 at 12:31 PM, Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org> wrote:
> On Monday 21 January 2013, Gregory CLEMENT wrote:
>> @@ -1624,7 +1624,7 @@ config LOCAL_TIMERS
>>         bool "Use local timer interrupts"
>>         depends on SMP
>>         default y
>> -       select HAVE_ARM_TWD if (!ARCH_MSM_SCORPIONMP && !EXYNOS4_MCT)
>> +       select HAVE_ARM_TWD if (!ARCH_MSM_SCORPIONMP && !EXYNOS4_MCT && !ARMADA_370_XP_TIMER)
>>
>
> Maybe it can be written as
>
> config LOCAL_TIMERS
>         bool "Use local timer interrupts"
>         depends on SMP
>         default y
>
> config HAVE_ARM_TWD
>         depends on LOCAL_TIMERS
>         default ARCH_MULTIPLATFORM || (!ARCH_MSM_SCORPIONMP && !EXYNOS4_MCT)
>         default y
>
> This will still be slightly wrong (generating extra code) on a multiplatform
> kernel that has no platform other than MSM or EXYNOS, but the other alternative
> would be that each platform with TWD support has to select HAVE_ARM_TWD itself.

Why would having each platform with TWD support select HAVE_ARM_TWD be
a problem?

If we look at it logically, this is the most efficient solution in
terms of brevity of the (already huge) Kconfig.

On multiplatform kernels where at least one arch has TWD support, it
will be included, and where not, it will not.

It doesn't seem logical for a feature descriptor (HAVE_ARM_TWD) to
rely on greater knowledge of what platforms may or may not support it.
If we had to include every platform in that list it would be unwieldy.

Which leads me to this; I wonder if there should be a policy document
that basically describes what HAVE_* really is meant for, and how
dependencies on ARCH_* (or MACH_* in the world of multiplatform)
should be handled for architectural features? That way there's a
little more fixed definition of how Kconfigs should be written to
effectively support multiplatform kernels and allow people to identify
misuses and get rid of them for multiplatform, if only just to get the
information out of the heads of maintainers and into a file somewhere
that we can reference... maybe it exists already but I am missing it?

--
Matt Sealey <matt-sEEEE4iEDtaXzmuOJsdVMQ@public.gmane.org>
Product Development Analyst, Genesi USA, Inc.