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

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Date:	Fri, 9 Jan 2015 02:09:25 +0000 (UTC)
From:	Paul Walmsley <paul@...an.com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
cc:	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

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.

> 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?

> One comment below.

> > diff --git a/drivers/clocksource/tegra20_timer.c
> > b/drivers/clocksource/tegra20_timer.c
> > index d2616ef16770..83a8f5c9e139 100644
> > --- a/drivers/clocksource/tegra20_timer.c
> > +++ b/drivers/clocksource/tegra20_timer.c
> > @@ -29,8 +29,10 @@
> >   #include <linux/sched_clock.h>
> >   #include <linux/delay.h>
> > 
> > +#ifdef CONFIG_ARM
> >   #include <asm/mach/time.h>
> >   #include <asm/smp_twd.h>
> 
> Is smp_twd.h really needed ?
> 
> > +#endif

No, it can be removed.  

Would you be willing to ack or merge a revision of this patch with 

1. the #include <asm/smp_twd.h> removed

2. a larger number of changed lines, in order to minimize the number of 
new #ifdefs?




- Paul
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