Message-ID: <54AFD688.5000304@linaro.org>
Date:	Fri, 09 Jan 2015 14:24:24 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Thierry Reding <thierry.reding@...il.com>
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 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.


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