Re: [GIT PULL 1/3] ARM: soc: exynos: Drivers for v4.9

From	Krzysztof Kozlowski <krzk@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [GIT PULL 1/3] ARM: soc: exynos: Drivers for v4.9
Date	2016-09-19 18:00 +0200
Message-ID	<sj998-7ii-21@gated-at.bofh.it> (permalink)
References	<siNrY-22E-17@gated-at.bofh.it> <siNrY-22E-23@gated-at.bofh.it> <sj8mJ-71A-3@gated-at.bofh.it>
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On Mon, Sep 19, 2016 at 05:02:40PM +0200, Arnd Bergmann wrote:
> On Sunday, September 18, 2016 6:39:46 PM CEST Krzysztof Kozlowski wrote:
> > Samsung drivers/soc update for v4.9:
> > 1. Allow compile testing of exynos-mct clocksource driver on ARM64.
> > 2. Document Exynos5433 PMU compatible (already used by clkout driver and more
> >    will be coming soon).
> 
> Pulled into next/drivers, thanks
> 
> Just for my understanding: why do we need the exynos-mct driver on ARM64
> but not the delay-timer portion of it?

I think we want all of it but Doug's optimization 3252a646aa2c
("clocksource: exynos_mct: Only use 32-bits where possible") is not
ARM64 friendly. One way of dealing with it would be to prepare two
versions of exynos4_read_current_timer(). One reading only lower 32-bit
value for ARMv7 and second (slow) reading lower and upper for ARMv8.

> 
> Is there an advantage in using MCT over the architected timer on these
> chips? If so, should we also have a way to use it as the delay timer?

No, there is no real advantage... except that the SoC has some
interesting "characteristics"... The timers are tightly coupled. Very
tightly. I spent a lot of time and failed to boot my ARMv8 board without
some MCT magic.

Best regards,
Krzysztof

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[GIT PULL 0/3] ARM: exynos: Second round of stuff for v4.9 Krzysztof Kozlowski <krzk@kernel.org> - 2016-09-18 18:50 +0200
  [GIT PULL 1/3] ARM: soc: exynos: Drivers for v4.9 Krzysztof Kozlowski <krzk@kernel.org> - 2016-09-18 18:50 +0200
    Re: [GIT PULL 1/3] ARM: soc: exynos: Drivers for v4.9 Arnd Bergmann <arnd@arndb.de> - 2016-09-19 17:10 +0200
      Re: [GIT PULL 1/3] ARM: soc: exynos: Drivers for v4.9 Krzysztof Kozlowski <krzk@kernel.org> - 2016-09-19 18:00 +0200

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