linux-kernel - Re: [PATCH 5/6] RTC: SMBus support for the M41T80, etc. driver (#2)

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Message-Id: <20080518.003157.126143021.anemo@mba.ocn.ne.jp>
Date:	Sun, 18 May 2008 00:31:57 +0900 (JST)
From:	Atsushi Nemoto <anemo@....ocn.ne.jp>
To:	macro@...ux-mips.org
Cc:	khali@...ux-fr.org, a.zummo@...ertech.it,
	akpm@...ux-foundation.org, dwmw2@...radead.org,
	ralf@...ux-mips.org, tglx@...utronix.de,
	rtc-linux@...glegroups.com, i2c@...sensors.org,
	linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] RTC: SMBus support for the M41T80, etc. driver (#2)

On Tue, 13 May 2008 17:57:52 +0100 (BST), "Maciej W. Rozycki" <macro@...ux-mips.org> wrote:
> > You will do this even if all the registers were read as a block and the
> > RTC latched the register values so they have to be correct. Isn't it a
> > bit unfair / inefficient? If client->adapter has the
> > I2C_FUNC_SMBUS_READ_I2C_BLOCK functionality you can skip the comparison
> > and retry mechanism completely, saving some time and CPU cycles.
> 
>  Well, actually there is a reason beyond that.  It may change if we
> support subsecond resolution, but we currently do not.  The reason is if
> we return the original timestamp and the seconds register changes while
> the timestamp is being read, then effectively we return a value that is
> off by one second.  This is why for seconds I decided to return the second
> value read all the time.

I suppose the "off by one second" issue is not the matter each driver
should take care of.  This race is common for most RTC chip.

I do not have strong opinion for optimization suggested by Jean.  It
might be better, but I'm OK with current your patch.

---
Atsushi Nemoto
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