linux-kernel - Re: RTC , ds1307 I2C driver and NTP does not work.

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Message-Id: <20061118151923.6044d956.khali@linux-fr.org>
Date:	Sat, 18 Nov 2006 15:19:23 +0100
From:	Jean Delvare <khali@...ux-fr.org>
To:	"Joakim Tjernlund" <joakim.tjernlund@...nsmode.se>,
	Kumar Gala <galak@...nel.crashing.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, i2c@...sensors.org
Subject: Re: RTC , ds1307 I2C driver and NTP does not work.

On Fri, 17 Nov 2006 18:38:10 +0100, Joakim Tjernlund wrote:
> On Nov 17, 2006, at 10:38 AM, Joakim Tjernlund wrote:
> 
> > I get this when I activathte NTP and ntp "sync" the time the I2C HW  
> > clock.
> 
> You may be better off posting this to lkml and copy the i2c list (and  
> rtc if one exists).  Since its more a driver issue than anything  
> really ppc specific.  Clearly we are doing schedules() in mpc_xfer()  
> and maybe we shouldn't be.

It's OK to schedule or sleep in mpc_xfer. It's not OK to call mpc_xfer
from an interrupt context, which is what appears to be happening here.
So the ds1307 driver would need to be changed not to directly call
i2c_transfer from the interrupt. Using a workqueue should work.

That being said, I wonder why one would want to set the time from an
interrupt context in the first place. Maybe that's what needs fixing.

> > BUG: scheduling while atomic: swapper/0x00010000/0
> > Call Trace:^M
> > [C0245C80] [C000860C] show_stack+0x48/0x194 (unreliable)
> > [C0245CB0] [C01BEFF4] schedule+0x5d4/0x618
> > [C0245CF0] [C01BF9C8] schedule_timeout+0x70/0xd0
> > [C0245D30] [C014416C] i2c_wait+0x164/0x1d8
> > [C0245D80] [C0144490] mpc_xfer+0x2b0/0x3a8
> > [C0245DD0] [C01423E8] i2c_transfer+0x58/0x7c
> > [C0245DF0] [C0141124] ds1307_set_time+0x1bc/0x234
> > [C0245E00] [C013F82C] rtc_set_time+0xb0/0xb8^M
> > [C0245E20] [C000BFC4] set_rtc_class_time+0x34/0x58
> > [C0245E40] [C000C8D0] timer_interrupt+0x5a0/0x5fc
> > [C0245EE0] [C000F7B0] ret_from_except+0x0/0x14
> > --- Exception: 901 at cpu_idle+0xc8/0xf0
> >     LR = cpu_idle+0xec/0xf0
> > [C0245FC0] [C000388C] rest_init+0x28/0x38
> > [C0245FD0] [C01F36E0] start_kernel+0x1d8/0x228
> > [C0245FF0] [00003438] 0x3438
> >
> > I have activated RTC CLASS and have this in my board file:
> > #ifdef CONFIG_RTC_CLASS
> > late_initcall(rtc_class_hookup);
> > #endif
> >
> > kernel 2.6.19-rc5
> >
> >  Jocke

-- 
Jean Delvare
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