acpi_gsb_i2c_write_bytes() returns i2c_transfer()'s return value, which
is the number of transfers executed on success, so 1.

The ACPI code expects us to store 0 in gsb->status for success, not 1.

Specifically this breaks the following code in the Thinkpad 8 DSDT:

            ECWR = I2CW = ECWR /* \_SB_.I2C1.BAT0.ECWR */
            If ((ECST == Zero))
            {
                ECRD = I2CR /* \_SB_.I2C1.I2CR */
            }

Before this commit we set ECST to 1, causing the read to never happen
breaking battery monitoring on the Thinkpad 8.

This commit makes acpi_gsb_i2c_write_bytes() return 0 when i2c_transfer()
returns 1, so the single write transfer completed successfully, and
makes it return -EIO on for other (unexpected) return values >= 0.

Cc: stable@vger.kernel.org
Signed-off-by: Hans de Goede <redacted>
---
Changes in v2:
-Modify the value which acpi_gsb_i2c_write_bytes() returns instead of
 checking + modifying the return value in its caller
---
 drivers/i2c/i2c-core-acpi.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/i2c-core-acpi.c b/drivers/i2c/i2c-core-acpi.c
index 7c3b4740b94b..b8f303dea305 100644
--- a/drivers/i2c/i2c-core-acpi.c
+++ b/drivers/i2c/i2c-core-acpi.c

@@ -482,11 +482,16 @@ static int acpi_gsb_i2c_write_bytes(struct i2c_client *client,
 	msgs[0].buf = buffer;
 
 	ret = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs));
-	if (ret < 0)
-		dev_err(&client->adapter->dev, "i2c write failed\n");
 
 	kfree(buffer);
-	return ret;
+
+	if (ret < 0) {
+		dev_err(&client->adapter->dev, "i2c write failed: %d\n", ret);
+		return ret;
+	}
+
+	/* 1 transfer must have completed successfully */
+	return (ret == 1) ? 0 : -EIO;
 }
 
 static acpi_status

-- 
2.18.0