Subject: Re: [PATCH] i2c-mpc: work around missing-9th-clock-pulse bug

From: Jean Delvare <[email-masked]>
Date: Tue, 10 Jul 2007 14:40:30 +0200

Hi Grant, hi Domen,

On Tue, 10 Jul 2007 00:22:05 -0600, Grant Likely wrote:
> On 7/10/07, Domen Puncer <[email-masked]> wrote:
> > Work around a problem reported on:
> > http://ozlabs.org/pipermail/linuxppc-embedded/2005-July/019038.html
> > Without this patch I2C on mpc5200 becomes unusable after a while.
> > Tested on mpc5200 boards by Matthias and me.
> >
> >
> > Signed-off-by: Domen Puncer <[email-masked]>
> 
> Looks good to me,
> 
> Acked-by: Grant Likely <[email-masked]>

OK, I will take this patch, but I'd like you to add a comment before
mpc_i2c_fixup() explaining what exactly the problem is and how it is
worked around. Otherwise it's a bit obscure what is going on.

I guess you want this patch in 2.6.23-rc1?

> > ---
> >  drivers/i2c/busses/i2c-mpc.c |   17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> >
> > Index: work-powerpc.git/drivers/i2c/busses/i2c-mpc.c
> > ===================================================================
> > --- work-powerpc.git.orig/drivers/i2c/busses/i2c-mpc.c
> > +++ work-powerpc.git/drivers/i2c/busses/i2c-mpc.c
> > @@ -74,6 +74,20 @@ static irqreturn_t mpc_i2c_isr(int irq,
> >         return IRQ_HANDLED;
> >  }
> >
> > +static void mpc_i2c_fixup(struct mpc_i2c *i2c)
> > +{
> > +       writeccr(i2c, 0);
> > +       udelay(30);
> > +       writeccr(i2c, CCR_MEN);
> > +       udelay(30);
> > +       writeccr(i2c, CCR_MSTA | CCR_MTX);
> > +       udelay(30);
> > +       writeccr(i2c, CCR_MSTA | CCR_MTX | CCR_MEN);
> > +       udelay(30);
> > +       writeccr(i2c, CCR_MEN);
> > +       udelay(30);
> > +}
> > +
> >  static int i2c_wait(struct mpc_i2c *i2c, unsigned timeout, int writing)
> >  {
> >         unsigned long orig_jiffies = jiffies;
> > @@ -153,6 +167,7 @@ static void mpc_i2c_start(struct mpc_i2c
> >  static void mpc_i2c_stop(struct mpc_i2c *i2c)
> >  {
> >         writeccr(i2c, CCR_MEN);
> > +       writeccr(i2c, 0);
> >  }
> >
> >  static int mpc_write(struct mpc_i2c *i2c, int target,
> > @@ -245,6 +260,8 @@ static int mpc_xfer(struct i2c_adapter *
> >                 }
> >                 if (time_after(jiffies, orig_jiffies + HZ)) {
> >                         pr_debug("I2C: timeout\n");
> > +                       if (readb(i2c->base + MPC_I2C_SR) == (CSR_MCF | CSR_MBB | CSR_RXAK))
> > +                               mpc_i2c_fixup(i2c);
> >                         return -EIO;
> >                 }
> >                 schedule();
> >

-- 
Jean Delvare