i2c: core: ACPI: Log device not acking errors at dbg loglevel

Unfortunately some DSDTs issue bogus i2c reads to non existing devices
resulting in -EREMOTEIO errors because the non existing device of course
does not ack.

This happens e.g. from the The Asus T100TA's _BIX method, the DSDT on
the T100TA defines 2 resources on the I2C1 bus:

        Name (EHID, ResourceTemplate ()
        {
            I2cSerialBusV2 (0x005B, ControllerInitiated, 0x00061A80,
                AddressingMode7Bit, "\\_SB.I2C1",
                0x00, ResourceConsumer, , Exclusive,
                )
        })
        OperationRegion (EHOR, GenericSerialBus, Zero, 0x0100)
        Field (EHOR, BufferAcc, NoLock, Preserve)
        {
            Connection (EHID),
            Offset (0x01),
            AccessAs (BufferAcc, AttribBytes (0x10)),
            ABCD,   8
        }

        Name (UMPC, ResourceTemplate ()
        {
            I2cSerialBusV2 (0x0066, ControllerInitiated, 0x00061A80,
                AddressingMode7Bit, "\\_SB.I2C1",
                0x00, ResourceConsumer, , Exclusive,
                )
        })

The _BIX method does a single read (on each BIX() call) from the EHID
device through the ABCD Field, only to completely ignore the result.
This read always fails as there is no i2c client at address 0x5b.

The _BIX method also does several reads from the UMPC device and actually
uses the results of those to provide battery information.

IIRC I've also seen some DSTDs which do an i2c read to detect if a device
is present, also leading to false positive errors being logged.

Esp. the _BIX use is problematic as the _BIX method gets called
periodically to monitor battery status.

This commit stops the logs from filling up with errors like these:

[   57.327858] i2c i2c-0: i2c read 16 bytes from client@0x5b starting at
               reg 0x1 failed, error: -121
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/i2c-core-acpi.c

@@ -445,11 +445,17 @@ static int acpi_gsb_i2c_read_bytes(struct i2c_client *client,
 	msgs[1].buf = buffer;
 
 	ret = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs));
-	if (ret < 0)
-		dev_err(&client->adapter->dev, "i2c read %d bytes from client@%#x starting at reg %#x failed, error: %d\n",
+	if (ret < 0) {
+		/* Getting a NACK is unfortunately normal with some DSTDs */
+		if (ret == -EREMOTEIO)
+			dev_dbg(&client->adapter->dev, "i2c read %d bytes from client@%#x starting at reg %#x failed, error: %d\n",
 				data_len, client->addr, cmd, ret);
 		else
+			dev_err(&client->adapter->dev, "i2c read %d bytes from client@%#x starting at reg %#x failed, error: %d\n",
+				data_len, client->addr, cmd, ret);
+	} else {
 		memcpy(data, buffer, data_len);
+	}
 
 	kfree(buffer);
 	return ret;