Re: [PATCH] i2c: Make sure i2c_algo_bit_data.timeout is HZ-independent

[Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>]

On Mon, 23 Feb 2009 10:00:12 -0500, Lennart Sorensen wrote:
> On Sun, Feb 22, 2009 at 12:50:05PM +0100, Jean Delvare wrote:
> > i2c_algo_bit_data.timeout is supposed to be in jiffies, so drivers
> > should use set this value in terms of HZ.
> > 
> > Ultimately I think this field should be discarded in favor of
> > i2c_adapter.timeout, but that's left for a future patch.
> > 
> > Signed-off-by: Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>
> > Cc: Russell King <rmk+kernel-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>
> > Cc: Lennert Buytenhek <kernel-OLH4Qvv75CYX/NnBR394Jw@public.gmane.org>
> > Cc: Len Sorensen <lsorense-1wCw9BSqJbv44Nm34jS7GywD8/FfD2ys@public.gmane.org>
> > ---
> >  drivers/i2c/busses/i2c-acorn.c   |    2 +-
> >  drivers/i2c/busses/i2c-ixp2000.c |    2 +-
> >  drivers/i2c/busses/scx200_i2c.c  |    2 +-
> >  3 files changed, 3 insertions(+), 3 deletions(-)
> > 
> > --- linux-2.6.29-rc5.orig/drivers/i2c/busses/scx200_i2c.c	2009-02-22 12:32:33.000000000 +0100
> > +++ linux-2.6.29-rc5/drivers/i2c/busses/scx200_i2c.c	2009-02-22 12:32:45.000000000 +0100
> > @@ -76,7 +76,7 @@ static struct i2c_algo_bit_data scx200_i
> >  	.getsda		= scx200_i2c_getsda,
> >  	.getscl		= scx200_i2c_getscl,
> >  	.udelay		= 10,
> > -	.timeout	= 100,
> > +	.timeout	= HZ,
> >  };
> 
> OK.  Well I know the driver has worked for me with both HZ=100 and now
> HZ=1000, so making it consistent sounds good to me.  I think a lot of
> people thought it was in microseconds or miliseconds.

It was clarified in i2c-algo-bit.h in kernel version 2.5.54, that's
quite a while ago. The problem is that i2c-algo-bit.c itself had it
wrong.

At HZ=1000, 100 jiffies is 100 ms, that's already a reasonably long
timeout. And not that many slaves actually stretch the I2C clock.

-- 
Jean Delvare