linux-kernel - Re: [PATCH] clocksource: tegra: wrap arch/arm-specific sections in CONFIG

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Date:	Fri, 9 Jan 2015 14:33:51 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:	Paul Walmsley <paul@...an.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-tegra@...r.kernel.org, Allen Martin <amartin@...dia.com>,
	Stephen Warren <swarren@...dia.com>,
	Thierry Reding <treding@...dia.com>,
	Alexandre Courbot <gnurou@...il.com>, pwalmsley@...dia.com
Subject: Re: [PATCH] clocksource: tegra: wrap arch/arm-specific sections in
 CONFIG_ARM

On Fri, Jan 09, 2015 at 02:24:24PM +0100, Daniel Lezcano wrote:
> On 01/09/2015 01:21 PM, Thierry Reding wrote:
> >On Fri, Jan 09, 2015 at 09:31:08AM +0100, Daniel Lezcano wrote:
> >>On 01/09/2015 03:09 AM, Paul Walmsley wrote:
> >>>Hello Daniel
> >>>
> >>>On Thu, 8 Jan 2015, Daniel Lezcano wrote:
> >>>
> >>>>On 12/09/2014 11:07 PM, Paul Walmsley wrote:
> >>>>>
> >>>>>Like several of the other files in drivers/clocksource,
> >>>>>tegra20_timer.c contains code that can only compile when CONFIG_ARM is
> >>>>>enabled.  This causes obvious problems when trying to compile this
> >>>>>code for NVIDIA ARM64-based SoCs, such as Tegra132.  The same timer IP
> >>>>>blocks exist, so it seems appropriate to provide support for them.
> >>>>>
> >>>>>So until we figure out a better way to partition this code, wrap the
> >>>>>delay_timer and persistent_clock support code with preprocessor tests
> >>>>>for CONFIG_ARM.
> >>>>>
> >>>>>  (The delay_timer code should not be needed at all on
> >>>>>ARM64 due to the presence of the ARMv8 architected timer.  The
> >>>>>persistent_clock support code could become important once power
> >>>>>management modes are implemented that turn off the CPU complex.)
> >>>>
> >>>>IIUC, the cpuidle driver is not yet ready, right ?
> >>>>
> >>>>If it is the case, this driver is not needed yet, no ?
> >>>
> >>>The point of the patch is to allow the hardware drivers selected by
> >>>CONFIG_ARCH_TEGRA to build for an arm64 kernel, just as they build for
> >>>32-bit ARM.
> >>>
> >>>There's nothing CPUIdle-specific about the patch - that is, this timer can
> >>>be selected as a clockevent and clocksource provider without the use of
> >>>CPUIdle - although low-power PM idle is likely to be a primary use-case.
> >>
> >>What I meant is this timer is not needed for the moment.
> >>
> >>>>Perhaps you can rework a bit this driver in the meantime to have a better fix
> >>>>than disabling the code with macros ?
> >>>
> >>>I'm happy to do that, but it would be nice to get the driver compiling
> >>>first for ARM64 :-)
> >>>
> >>>>Otherwise, please try at least to group the code into a minimal set of macros.
> >>>
> >>>So, would it be accurate to say that you would prefer a patch that changes
> >>>more lines of code, but minimizes preprocessor directives, to the current
> >>>patch?
> >>
> >>Yes at least an attempt to factor out a bit the driver. Those #ifdef are
> >>like #if 0, which is a quick fix. I am not strongly against this patch, but
> >>it would be nice to take the opportunity to reorganize it a bit.
> >
> >How about we do something like the attached patch instead for now. That
> >avoids any #ifdef'ery and still we don't attempt (and fail) to build the
> >driver on 64-bit ARM.
> >
> >With that applied we can incrementally make the changes to untangle the
> >ARM-specific parts and when the driver can build on 64-bit ARM we simply
> >select TEGRA_TIMER via Kconfig.
> 
> Yes, that is exactly what I was thinking about after sending the previous
> email. And by this way, you also fixed the Kconfig option selection logic.

Great. Will you give your Acked-by so that I can take that patch through
the Tegra tree to resolve the build dependency?

Thierry

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