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

Subject: Re: [PATCH 5/6] RTC: SMBus support for the M41T80, etc. driver (#2)
From: Atsushi Nemoto <>
Date: Sun, 18 May 2008 00:31:57 +0900 (JST)
In-reply-to: <>
Original-recipient: rfc822;
References: <> <20080513140444.49d7a044@hyperion.delvare> <>
On Tue, 13 May 2008 17:57:52 +0100 (BST), "Maciej W. Rozycki" 
<> 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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