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

[Domen Puncer]

On 11/07/07 00:03 -0600, Grant Likely wrote:
> On 7/10/07, Domen Puncer <domen.puncer at telargo.com> wrote:
> >On 10/07/07 14:40 +0200, Jean Delvare wrote:
...
> >+/* 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
> >+ */
> 
> I don't think it's a great idea to use a link;  You should copy the
> important parts into the .c file.  Archives may not be forever, and
> links cannot be read when offline.  If the text is too long for the
> middle of the C file; then put the documentation at the top right
> after the header block.

And v4:
<----------- 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 <domen.puncer at telargo.com>

---
 drivers/i2c/busses/i2c-mpc.c |   22 ++++++++++++++++++++++
 1 file changed, 22 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 +74,25 @@ static irqreturn_t mpc_i2c_isr(int irq, 
 	return IRQ_HANDLED;
 }
 
+/* Sometimes 9th clock pulse isn't generated, and slave doesn't release
+ * the bus, because it wants to send ACK.
+ * Following sequence of enabling/disabling and sending start/stop generates
+ * the pulse, so it's all OK.
+ */
+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 +172,7 @@ 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 +265,8 @@ 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();