Re: [PATCH] i2c: i2c-omap: Fix standard and fast mode prescalers

[Tony Lindgren <tony@atomide.com>]

* Eero Nurkkala <ext-eero.nurkkala@nokia.com> [081127 10:39]:
> We scope-verified these scl and sch values for 100 and 400 kHz busses.
> Now they're in the specs.

Pushing to l-o tree and adding to omap-fixes queue for mainline.

Tony

> On Wed, 2008-11-26 at 15:44 +0200, ext-eero.nurkkala@nokia.com wrote:
> > From: Eero Nurkkala <ext-eero.nurkkala@nokia.com>
> > 
> > The prescalers for 100 kHz and 400 kHz mode
> > are wrong for omap 3430 and omap 2430. The
> > internal clock is the fclock divided by the
> > prescaler. The PSC is an 8 bit field in
> > omap3430 and omap2430. Moreover, the scll and
> > sclh values should be adjusted properly.
> > Having the correct prescaler is important in
> > the process of getting a finite i2c clock. In
> > addition, the prescaler is used in the process
> > of activating the correct noise filter and thus,
> > lets more error resilient i2c communications.
> > 
> > Signed-off-by: Eero Nurkkala <ext-eero.nurkkala@nokia.com>
> > ---
> >  drivers/i2c/busses/i2c-omap.c |   12 +++++++++---
> >  1 files changed, 9 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
> > index 630702c..c21af3f 100644
> > --- a/drivers/i2c/busses/i2c-omap.c
> > +++ b/drivers/i2c/busses/i2c-omap.c
> > @@ -337,7 +337,13 @@ static int omap_i2c_init(struct omap_i2c_dev *dev)
> >  	if (cpu_is_omap2430() || cpu_is_omap34xx()) {
> >  
> >  		/* HSI2C controller internal clk rate should be 19.2 Mhz */
> > -		internal_clk = 19200;
> > +		if (dev->speed > 400)
> > +			internal_clk = 19200;
> > +		else if (dev->speed > 100)
> > +			internal_clk = 9600;
> > +		else
> > +			internal_clk = 4000;
> > +
> >  		fclk_rate = clk_get_rate(dev->fclk) / 1000;
> >  
> >  		/* Compute prescaler divisor */
> > @@ -355,8 +361,8 @@ static int omap_i2c_init(struct omap_i2c_dev *dev)
> >  			hssclh = fclk_rate / (dev->speed * 2) - 6;
> >  		} else {
> >  			/* To handle F/S modes */
> > -			fsscll = internal_clk / (dev->speed * 2) - 6;
> > -			fssclh = internal_clk / (dev->speed * 2) - 6;
> > +			fsscll = internal_clk / (dev->speed * 2) - 3;
> > +			fssclh = internal_clk / (dev->speed * 2) - 9;
> >  		}
> >  		scll = (hsscll << OMAP_I2C_SCLL_HSSCLL) | fsscll;
> >  		sclh = (hssclh << OMAP_I2C_SCLH_HSSCLH) | fssclh;
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-omap" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html