Return-Path: Received: from buildserver.ru.mvista.com (unknown [85.21.88.6]) by ozlabs.org (Postfix) with ESMTP id AB867DE4E2 for ; Wed, 21 May 2008 00:35:54 +1000 (EST) Date: Tue, 20 May 2008 18:35:53 +0400 From: Anton Vorontsov To: Kumar Gala Subject: Re: [PATCH 1/7] [POWERPC] sysdev: implement FSL GTM support Message-ID: <20080520143553.GA22450@polina.dev.rtsoft.ru> References: <20080519174558.GA26229@polina.dev.rtsoft.ru> <20080519174651.GA28185@polina.dev.rtsoft.ru> <20080520123226.GB14573@polina.dev.rtsoft.ru> <7A841A6C-137D-4784-B7B0-2BAFFFB0CCF7@kernel.crashing.org> <20080520140847.GA2430@polina.dev.rtsoft.ru> <20080520143234.GA19707@polina.dev.rtsoft.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 In-Reply-To: <20080520143234.GA19707@polina.dev.rtsoft.ru> Cc: Scott Wood , linuxppc-dev@ozlabs.org, Timur Tabi Reply-To: avorontsov@ru.mvista.com List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, May 20, 2008 at 06:32:34PM +0400, Anton Vorontsov wrote: > On Tue, May 20, 2008 at 09:20:50AM -0500, Kumar Gala wrote: > >>>>> This is explained in the .c file with a kernel doc. Basically the > >>>> difference is that timer16 could silently crop the precision, while > >>>> utimer16 could not thus explicitly accepts u16 argument (max. timer > >>>> interval with usec precision fits in u16). > >>> > >>> Maybe I'm confused what the utility is of cropping the precision in > >>> this > >>> way is. I'd also say that _timer16 is poorly named to convey the > >>> behavior. I'm not sure what to call it because I still dont get > >>> exactly > >>> why you'd want the precision cropped. > >> > >> Precision matters for FHCI-like drivers, when driver, for example, > >> schedule transactions via the GTM timers, and there timings matters > >> a lot. > >> > >> Though, timer16 crops the precision _only_ if usecs > 65535, so FHCI > >> _can_ still use the _timer16 (because FHCI does not request intervals > >>> 65535). But I implemented two function because: > >> > >> 1. I think we don't need unnecessary stuff in the ISRs (this is weak > >> argument since I didn't measure the impact). > >> 2. I wanted to make the API clear (seem to fail this undertaking :-), > >> which functions will behave exactly the way you asked it (utimer16), > >> and which functions will _silently_ crop the precision (timer16) > >> (if asked for 1001000 usecs, it will give you ~~1001000, depending > >> on the GTM frequency). > > > > I'm fine w/having both. I think they are poorly named. I'd also call > > them _set_timer but that's just me. > > > > Maybe something w/the term _exact_ in the name. Is it the case w/the > > precise form we'd have no prescaling (if so maybe a comment in the API > > about that would help clarity)? > > We're always prescale [to 1000000 MHz for usec precision]. -MHz +Hz -- Anton Vorontsov email: cbouatmailru@gmail.com irc://irc.freenode.net/bd2