linux-kernel - Re: [rtc-linux] Re: invalid default values in RTC chip

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Message-ID: <20081016234108.1268f65c@i1501.lan.towertech.it>
Date:	Thu, 16 Oct 2008 23:41:08 +0200
From:	Alessandro Zummo <alessandro.zummo@...ertech.it>
To:	rtc-linux@...glegroups.com
Cc:	akpm@...ux-foundation.org,
	Jüri Reitel <juri.reitel@...wenthal.ee>,
	linux-kernel@...r.kernel.org, David Brownell <david-b@...bell.net>,
	Jean Delvare <khali@...ux-fr.org>,
	Rodolfo Giometti <giometti@...ux.it>
Subject: Re: [rtc-linux] Re: invalid default values in RTC chip

On Thu, 16 Oct 2008 13:58:46 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> > My question relates to RTC driver linux/drivers/rtc/rtc-ds1307.c for 
> > device m41t00. Driver probe function will fail if some of the chip's 
> > registers contain invalid date time values i.e. if month register is 32 
> > or minutes is 61. Is this correct behavior? Probe function's purpose is 
> > to check if the device is as was assumed (this time RTC and it is). The 
> > chip's values are incorrect but the chip works, even the m41t00 chip 
> > manual states that after initial powerup (RTC battery power applied) 
> > internal registers will contain random data.
> > 
> > There are two solutions first is driver patch and another is i2c-dev and 
> > i2cset tool to use from user space during bootup. Whitch one should be used?

 Given we transitioned to the new i2c model, which mandates
 a platform device to be declared, there's no more the need
 to check for the device in the probing function.

 this should be fixed in the driver.

 however, a driver may still return a failure when reading
 the time if there are inappropriate values in the registers.

 the solution is to patch the driver for detection and then
 use a recent hwclock on bootup to write the time if required.


-- 

 Best regards,

 Alessandro Zummo,
  Tower Technologies - Torino, Italy

  http://www.towertech.it

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