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

From: Domen Puncer <[email-masked]>
Date: Wed, 11 Jul 2007 07:49:23 +0200

On 10/07/07 14:40 +0200, Jean Delvare wrote:
> 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.

OK.

> 
> I guess you want this patch in 2.6.23-rc1?

Yes.

So... v3:
<----------- cut ------------->

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 Fechner and me.

Signed-off-by: Domen Puncer <[email-masked]>

---
 drivers/i2c/busses/i2c-mpc.c |   21 +++++++++++++++++++++
 1 file changed, 21 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 +74,24 @@ static irqreturn_t mpc_i2c_isr(int irq, 
 	return IRQ_HANDLED;
 }
 
+/* Sometimes 9th clock pulse isn't generated, so slave doesn't release
+ * the bus.  Documented and suggested workaround on
+ * http://ozlabs.org/pipermail/linuxppc-embedded/2005-July/019038.html
+ */
+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 +171,7 @@ 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 +264,8 @@ 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();