Re: [PATCH v3 9/9] ARM: add initial support for Marvell Berlin SoCs

[Sebastian Hesselbarth]

On 11/08/2013 01:58 AM, Jisheng Zhang wrote:
> On Thu, 7 Nov 2013 13:22:35 -0800
> Sebastian Hesselbarth <sebastian.hesselbarth@xxxxxxxxx> wrote:
> > On 11/07/2013 05:20 PM, Arnd Bergmann wrote:
> > > On Thursday 07 November 2013, Sebastian Hesselbarth wrote:
> > > > Actually, IIRC smp_twd does not compile without SMP set, so the above
> > > > should at least be 'HAVE_ARM_TWD if SMP'. If you shrink MULTI_V7 down
> > > > to non-SMP cores, you can disable it and it will fail to compile.
> > >
> > > If there are UP-systems for which TWD is the best clocksource, we should
> > > probably fix the code to allow that configuration. IIRC there were already
> > > patches recently in this area, maybe it's already solved.
>
> The problems is twd is not mandatory in CA9 UP system, so it may not exist.
> However, I got answers from soc people, the BG2CD does configured and enabled
> TWD. so we are lucky and can add HAVE_TWD for BG2CD.

Jisheng,

thanks for backing this up. As I said, I tried it with barebox and TWD
is sufficient for a timer there.

Currently, Linux requires SMP for TWD - but as you confirmed, there are
non-SMP systems with TWD. The build errors below are just from a check
for SMP systems, so if we remove that, TWD should be ready for non-SMP.

I'll see, if I can prepare a patch next week and put it on list.

Sebastian

> > I just tried barebox bootloader to use TWD as timer on berlin2cd and it
> > perfectly works, i.e. with time related commands I can see the timer
> > register decreasing. So the timer is available on this UP SoC.
>
> Yep. It is available.
>
> > As said before, compiling linux without CONFIG_SMP but with
> > CONFIG_HAVE_ARM_TWD gives:
> >
> > warning: (SOC_OMAP5 && ARCH_ROCKCHIP && ARCH_SHMOBILE_MULTI &&
> > MACH_BERLIN_BG2 && MACH_BERLIN_BG2CD) selects HAVE_ARM_TWD which has
> > unmet direct dependencies (SMP)
> >
> > and
> >
> > arch/arm/kernel/smp_twd.c: In function 'twd_local_timer_of_register':
> > arch/arm/kernel/smp_twd.c:391: error: 'setup_max_cpus' undeclared (first
> > use in this function)
> > arch/arm/kernel/smp_twd.c:391: error: (Each undeclared identifier is
> > reported only once
> > arch/arm/kernel/smp_twd.c:391: error: for each function it appears in.)
> > make[1]: *** [arch/arm/kernel/smp_twd.o] Error 1
> >
> > I haven't looked deeper into this, but I guess it will not be hard
> > to make ARM_TWD independent of SMP.

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