[PATCH] Incremental i2c-mpc driver fix for multi-master i2c busses.

[PATCH] Incremental i2c-mpc driver fix for multi-master i2c busses.

[Clifford Wolf]

Incremental i2c-mpc driver fix for multi-master i2c busses.

This is an incremental bugfix for the i2c-mpc driver. It is based
on the bugfix I've sent on 2008-12-22:

	http://lkml.org/lkml/2008/12/22/99

There still was a remaining problem with multi-master i2c busses
when an i2c bus access is interrupted by a unix signal while
waiting for bus arbitration.

This is an extreamly rare case but I managed to stumble over it in
multi master i2c performance tests.

Tested with a freescale MPC8349E host cpu.

Signed-off-by: Clifford Wolf <clifford@clifford.at>

--- drivers/i2c/busses/i2c-mpc.c	(revision 2216)
+++ drivers/i2c/busses/i2c-mpc.c	(working copy)
@@ -105,7 +105,7 @@
 			schedule();
 			if (time_after(jiffies, orig_jiffies + timeout)) {
 				pr_debug("I2C: timeout\n");
-				writeccr(i2c, 0);
+				writeccr(i2c, CCR_MEN);
 				result = -EIO;
 				break;
 			}
@@ -119,10 +119,10 @@
 
 		if (unlikely(result < 0)) {
 			pr_debug("I2C: wait interrupted\n");
-			writeccr(i2c, 0);
+			writeccr(i2c, CCR_MEN);
 		} else if (unlikely(!(i2c->interrupt & CSR_MIF))) {
 			pr_debug("I2C: wait timeout\n");
-			writeccr(i2c, 0);
+			writeccr(i2c, CCR_MEN);
 			result = -ETIMEDOUT;
 		}
 
@@ -267,7 +267,7 @@
 	while (readb(i2c->base + MPC_I2C_SR) & CSR_MBB) {
 		if (signal_pending(current)) {
 			pr_debug("I2C: Interrupted\n");
-			writeccr(i2c, 0);
+			writeccr(i2c, CCR_MEN);
 			return -EINTR;
 		}
 		if (time_after(jiffies, orig_jiffies + HZ)) {
@@ -369,6 +369,15 @@
 		goto fail_add;
 	}
 
+	/* Make sure the adapter is already in master mode some time before
+	 * the first xfer to make sure arbitration control had enough time
+	 * to monitor the bus. The CCR_MEN flag should never be cleared without
+	 * makeing sure there is some delay between setting it again and
+	 * starting the first transfer..
+	 */
+	writeccr(i2c, CCR_MEN);
+	udelay(100);
+
 	return result;
 
       fail_add:

-- 
The great thing about Object Oriented code is that it can make small,
simple problems look like large, complex ones.

Re: [PATCH] Incremental i2c-mpc driver fix for multi-master i2c busses.

[Ben Dooks]

On Mon, Jan 05, 2009 at 02:21:02PM +0100, Clifford Wolf wrote:
> Incremental i2c-mpc driver fix for multi-master i2c busses.

Hi, you missed linux-i2c@vger.kernel.org which is the new home
for the i2c list. You should have received an auto-reply about
how this list has moved.

I'll probably try and get another merge out sometime this week.
 
> This is an incremental bugfix for the i2c-mpc driver. It is based
> on the bugfix I've sent on 2008-12-22:
> 
> 	http://lkml.org/lkml/2008/12/22/99
> 
> There still was a remaining problem with multi-master i2c busses
> when an i2c bus access is interrupted by a unix signal while
> waiting for bus arbitration.
> 
> This is an extreamly rare case but I managed to stumble over it in
> multi master i2c performance tests.
> 
> Tested with a freescale MPC8349E host cpu.
> 
> Signed-off-by: Clifford Wolf <clifford@clifford.at>
> 
> --- drivers/i2c/busses/i2c-mpc.c	(revision 2216)
> +++ drivers/i2c/busses/i2c-mpc.c	(working copy)
> @@ -105,7 +105,7 @@
>  			schedule();
>  			if (time_after(jiffies, orig_jiffies + timeout)) {
>  				pr_debug("I2C: timeout\n");
> -				writeccr(i2c, 0);
> +				writeccr(i2c, CCR_MEN);
>  				result = -EIO;
>  				break;
>  			}
> @@ -119,10 +119,10 @@
>  
>  		if (unlikely(result < 0)) {
>  			pr_debug("I2C: wait interrupted\n");
> -			writeccr(i2c, 0);
> +			writeccr(i2c, CCR_MEN);
>  		} else if (unlikely(!(i2c->interrupt & CSR_MIF))) {
>  			pr_debug("I2C: wait timeout\n");
> -			writeccr(i2c, 0);
> +			writeccr(i2c, CCR_MEN);
>  			result = -ETIMEDOUT;
>  		}
>  
> @@ -267,7 +267,7 @@
>  	while (readb(i2c->base + MPC_I2C_SR) & CSR_MBB) {
>  		if (signal_pending(current)) {
>  			pr_debug("I2C: Interrupted\n");
> -			writeccr(i2c, 0);
> +			writeccr(i2c, CCR_MEN);
>  			return -EINTR;
>  		}
>  		if (time_after(jiffies, orig_jiffies + HZ)) {
> @@ -369,6 +369,15 @@
>  		goto fail_add;
>  	}
>  
> +	/* Make sure the adapter is already in master mode some time before
> +	 * the first xfer to make sure arbitration control had enough time
> +	 * to monitor the bus. The CCR_MEN flag should never be cleared without
> +	 * makeing sure there is some delay between setting it again and
> +	 * starting the first transfer..
> +	 */
> +	writeccr(i2c, CCR_MEN);
> +	udelay(100);
> +
>  	return result;
>  
>        fail_add:

-- 
Ben (ben@fluff.org, http://www.fluff.org/)

  'a smiley only costs 4 bytes'

Re: [PATCH] Incremental i2c-mpc driver fix for multi-master i2c busses.

[Andrew Morton]

On Mon, 5 Jan 2009 14:21:02 +0100
Clifford Wolf <clifford@clifford.at> wrote:

> Incremental i2c-mpc driver fix for multi-master i2c busses.
> 
> This is an incremental bugfix for the i2c-mpc driver. It is based
> on the bugfix I've sent on 2008-12-22:
> 
> 	http://lkml.org/lkml/2008/12/22/99
> 
> There still was a remaining problem with multi-master i2c busses
> when an i2c bus access is interrupted by a unix signal while
> waiting for bus arbitration.
> 
> This is an extreamly rare case but I managed to stumble over it in
> multi master i2c performance tests.
> 
> Tested with a freescale MPC8349E host cpu.

That's not a very good changelog - it has basically no information,
apart from the linked-to original changelog.

And the linked-to changelog has no description of the bug which is
being fixed.

> --- drivers/i2c/busses/i2c-mpc.c	(revision 2216)
> +++ drivers/i2c/busses/i2c-mpc.c	(working copy)

Please prepare patches in `patch -p1' form:

--- a/drivers/i2c/busses/i2c-mpc.c
+++ a/drivers/i2c/busses/i2c-mpc.c