Re: [PATCH v2 3/4] ARM: EXYNOS: add Exynos Dual Cluster Support

[Dave Martin]

On Thu, Oct 17, 2013 at 06:04:13PM +0200, Daniel Lezcano wrote:
> On 10/17/2013 04:32 PM, Dave Martin wrote:
> > On Thu, Oct 17, 2013 at 12:45:29PM +0200, Daniel Lezcano wrote:
> >> On 10/14/2013 05:08 PM, Vyacheslav Tyrtov wrote:
> >>> From: Tarek Dakhran <t.dakhran@xxxxxxxxxxx>
> >>> 
> >>> Add EDCS(Exynos Dual Cluster Support) for Samsung Exynos5410 SoC.
> >>> This enables all 8 cores, 4 x A7 and 4 x A15 run at the same time.
> > 
> > [...]
> > 
> >>> +	__mcpm_cpu_down(cpu, cluster);
> >>> +
> >>> +	if (!skip_wfi) {
> >>> +		exynos_core_power_down(cpu, cluster);
> >>> +		wfi();
> >>> +	}
> >>> +}
> >> 
> >> I did not looked line by line but these functions looks very similar
> >> than the tc2_pm.c's function. no ?
> > 
> > This is true.
> > 
> >> May be some code consolidation could be considered here.
> >> 
> >> Added Nico and Lorenzo in Cc.
> >> 
> >> Thanks
> >>    -- Daniel
> > 
> > Nico can commnent further, but I think the main concern here was that
> > this code shouldn't be factored prematurely.
> 
> I do not share this opinion.
> 
> > There are many low-level platform specifics involved here, so it's
> > hard to be certain that all platforms could fit into a more abstracted
> > framework until we have some evidence to look at.
> > 
> > This could be revisited when we have a few diverse MCPM ports to
> > compare.
> 
> I am worried about seeing more and more duplicated code around the ARM
> arch (eg. arm[64]/kernel/smp.c arm64/kernel/smp.c).
> 
> The cpuidle drivers have been duplicated and it took a while before
> refactoring them, and it is not finished. The hotplug code have been
> duplicated and now it is very difficult to factor it out.
> 
> A lot of work have been done to consolidate the code across the
> different SoC since the last 2 years.
> 
> If we let duplicate code populate the different files, they will
> belong to different maintainers, thus different trees. Each SoC
> contributors will tend to add their small changes making the code to
> diverge more and more and making difficult to re-factor it later.

I think this is Nico's call, since he has more experience than I do
of how these things tend to play out in practice.

Cheers
---Dave

> I am in favor of preventing duplicate code entering in the kernel and
> force the contributors to improve the kernel in general, not just the
> small part they are supposed to work on. Otherwise, we are letting the
> kernel to fork itself, internally...
> 
> > The low-level A15/A7 cacheflush sequence is already being factored
> > by Nico [1].
> 
> Hopefully he did it :)
> 
> Thanks
>   -- Daniel
> 
> > [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2013-October/205085.html
> > [PATCH] ARM: cacheflush: consolidate single-CPU ARMv7 cache disabling code
> > 
> > [...]
> > 
> 
> 
> -- 
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