linux-kernel - Re: [PATCH] clocksource/drivers/tango-xtal: Replace code by clocksource_mmio

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Message-ID: <564B222E.5080209@sigmadesigns.com>
Date:	Tue, 17 Nov 2015 13:48:46 +0100
From:	Marc Gonzalez <marc_gonzalez@...madesigns.com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Linux ARM <linux-arm-kernel@...ts.infradead.org>,
	Arnd Bergmann <arnd@...db.de>,
	Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH] clocksource/drivers/tango-xtal: Replace code by
 clocksource_mmio_init

On 17/11/2015 13:22, Daniel Lezcano wrote:
> On 11/13/2015 01:20 PM, Marc Gonzalez wrote:
>> On 13/11/2015 11:58, Daniel Lezcano wrote:
>>
>>> The current code to initialize, register and read the clocksource is
>>> already factored out in mmio.c via the clocksource_mmio_init function.
>>>
>>> Factor out the code with the clocksource_mmio_init function.
>>
>> The reason I didn't like clocksource_mmio_init() is because it exports
>> 4 generic accessors.
>>
>> I guess this function makes more sense when all platforms are using it,
>> in an ARCH_MULTIPLATFORM kernel. (Also the accessors are probably quite
>> small, so the waste is probably minimal.)
> 
> Hi Marc,
> 
> it is not clear for me if you agree with this patch or not. Can you 
> clarify ?

[ Adding rmk as the original mmio.c author ]

Hello Daniel,

It's hard to give a straight answer. From my limited perspective (building
a kernel for Sigma boards only) I feel that mmio.c brings nothing. (As you
mentioned, it would be interesting to measure whether having reg_base in
the ctx, rather than as a global is better or worse for perf, though the
actual difference may be lost in the noise.)

On the other hand, I can see how a different perspective, such as yours,
may see benefits in having all drivers use the same APIs; and there may
be other savings for ARCH_MULTIPLATFORM builds with lots of platforms.

I guess if you think it is a good patch, I will defer to your experience.

I just wish Thomas would take a look at my mmio patch. I will make an
official submission, so that it can be properly shot down :-)

Regards.

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