[lm-sensors] [PATCH] i2c: Fix NACK detection in i2c-pasemi

[Olof Johansson <olof@lixom.net>]

i2c: Fix NACK detection in i2c-pasemi

Turns out we don't actually check the status to see if there was a
device out there to talk to, just if we had a timeout when doing so.

Add the proper check, so we don't falsly think there are devices
on the bus that are not there, etc.


Signed-off-by: Olof Johansson <olof@lixom.net>

---

On Wed, Oct 24, 2007 at 01:51:09PM +0200, Jean Delvare wrote:

> The question is, how do you manage to get that many errors reported,
> when I don't get any when loading the lm90 driver, despite the 6 I2C
> buses on my system. When you reach this point in the lm90 driver, it
> means that i2c-core successfully probed that there was a device at said
> address on the given bus. I have a hard time believing that you have
> chips at 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b, 0x4c, 0x4d and 0x4e on 3
> different I2C buses on your system.
> 
> It sounds like the underlying bus driver is broken and report chips
> where they aren't. What are these I2C buses? Their driver(s) needs
> fixing.

Crap, yeah, you're right. This was the only driver behaving this way
for me, and I didn't have another controller to test on.

The bug is indeed in our bus driver, we don't check for NACK's, only
timeouts (I was of the impresison that a nack would cause a timeout,
but that's obviously wrong).

Patch below. Thanks a bunch!


-Olof


diff --git a/drivers/i2c/busses/i2c-pasemi.c b/drivers/i2c/busses/i2c-pasemi.c
index 58e3271..a1d339e 100644
--- a/drivers/i2c/busses/i2c-pasemi.c
+++ b/drivers/i2c/busses/i2c-pasemi.c
@@ -51,6 +51,7 @@ struct pasemi_smbus {
 #define MRXFIFO_DATA_M	0x000000ff
 
 #define SMSTA_XEN	0x08000000
+#define SMSTA_MTN	0x00200000
 
 #define CTL_MRR		0x00000400
 #define CTL_MTR		0x00000200
@@ -98,6 +99,10 @@ static unsigned int pasemi_smb_waitready(struct pasemi_smbus *smbus)
 		status = reg_read(smbus, REG_SMSTA);
 	}
 
+	/* Got NACK? */
+	if (status & SMSTA_MTN)
+		return -ENODEV;
+
 	if (timeout < 0) {
 		dev_warn(&smbus->dev->dev, "Timeout, status 0x%08x\n", status);
 		reg_write(smbus, REG_SMSTA, status);

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