linux-kernel - Re: [PATCH 7/9] RFC: rtc: implement rtc_read

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Message-ID: <51BB565A.1010305@ahsoftware.de>
Date:	Fri, 14 Jun 2013 19:43:54 +0200
From:	Alexander Holler <holler@...oftware.de>
To:	John Stultz <john.stultz@...aro.org>
CC:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	rtc-linux@...glegroups.com, Thomas Gleixner <tglx@...utronix.de>,
	Alessandro Zummo <a.zummo@...ertech.it>
Subject: Re: [PATCH 7/9] RFC: rtc: implement rtc_read_timeval()

Am 14.06.2013 19:23, schrieb John Stultz:
> On 06/14/2013 09:52 AM, Alexander Holler wrote:
>> Some RTCs offer a higher resolution than seconds. To support reading such
>> high resolution timestamps from inside the kernel implement
>> rtc_read_timeval() and add a read_timeval to the rtc-ops.
>
> So I like the direction this patch is going. But if we're going to add a
> new interface, lets not use an already out-dated structure (timeval).
>
> Instead could you rework this to be timepsec based? Or ktime_t if its
> really internal only?

Sure, no problem. I wasn't aware timeval is out-dated and I've read 
somewhere in the sources a comment that ktime_t has to disappear. I had 
no clue if I should use timeval or timespec, and just have roled a dice 
to decide between timeval and timespec.

That "internal only" is only because I don't want to write changes for 
the userspace api to handle RTCs with greater precision than seconds. I 
don't have a writable RTC supporting such a precision and I want to 
leave this for people which are developing such devices and earning 
money with them.

Besides that, I have almost no knowledge about the userspace api for 
RTCs. If just looked a bit around in the in-kernel-ntp-sources for 
adjtimex, but that's all.

Please don't forget, my only motivation is to use an USB-RTC I've build 
myself to use with developer-boards without RTCs. All the other work 
like the support for higher precisions, the new hctosys or similiar is 
just because I let me trick to do that ;)

Regards,

Alexander Holler
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