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

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Message-ID: <54AF91CC.2090007@linaro.org>
Date:	Fri, 09 Jan 2015 09:31:08 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Paul Walmsley <paul@...an.com>
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

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.

>> 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?

Yes.

Thanks

   -- Daniel


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