Patch "i2c: mux: pca954x: fix i2c mux selection caching" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

i2c: mux: pca954x: fix i2c mux selection caching

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     i2c-mux-pca954x-fix-i2c-mux-selection-caching.patch

and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Russell King <[email protected]>
Date: Sat, 17 Dec 2016 12:10:56 +0000
Subject: i2c: mux: pca954x: fix i2c mux selection caching

From: Russell King <[email protected]>

commit 7f638c1cb0a1112dbe0b682a42db30521646686b upstream.

smbus functions return -ve on error, 0 on success. However, __i2c_transfer() have a different return signature - -ve on error, or number of buffers transferred (which may be zero or greater.)

The upshot of this is that the sense of the test is reversed when using the mux on a bus supporting the master_xfer method: we cache the value and never retry if we fail to transfer any buffers, but if we succeed, we clear the cached value.

Fix this by making pca954x_reg_write() return a negative error code for all failure cases.

---
 drivers/i2c/muxes/i2c-mux-pca954x.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

@@ -151,6 +151,9 @@ static int pca954x_reg_write(struct i2c_
 		buf[0] = val;
 		msg.buf = buf;
 		ret = __i2c_transfer(adap, &msg, 1);
+
+		if (ret >= 0 && ret != 1)
+			ret = -EREMOTEIO;
 	} else {
 		union i2c_smbus_data data;
 		ret = adap->algo->smbus_xfer(adap, client->addr,

@@ -179,7 +182,7 @@ static int pca954x_select_chan(struct i2
 	/* Only select the channel if its different from the last channel */
 	if (data->last_chan != regval) {
 		ret = pca954x_reg_write(muxc->parent, client, regval);
-		data->last_chan = ret ? 0 : regval;
+		data->last_chan = ret < 0 ? 0 : regval;
 	}
 
 	return ret;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/i2c-mux-pca954x-fix-i2c-mux-selection-caching.patch