Re: [PATCH] hwmon: (lm73) Make detection less problematic

[Robert Casanova <robertcasanova@xxxxxxxxxxxxxx>]

I can confirm that we have also observed the same behavior as this patch solves. Some devices do not behave properly when requested by word reads.

This patch also solves the problems discussed in a different thread [1].

Thanks Jean and Guenter.

References:

[1] http://lists.lm-sensors.org/pipermail/lm-sensors/2011-August/033621.html

On 30 August 2011 16:05, Jean Delvare <khali@xxxxxxxxxxxx> wrote:

Word reads can cause trouble with some I2C devices, so do as much
detection as we can using only byte reads, and only use a word read in
the end to confirm the positive match. Also properly handle read
errors.

Signed-off-by: Jean Delvare <khali@xxxxxxxxxxxx>
Cc: Guenter Roeck <guenter.roeck@xxxxxxxxxxxx>
Cc: Robert Casanova <robertcasanova@xxxxxxxxxxxxxx>
---
 drivers/hwmon/lm73.c |   22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

--- linux-3.1-rc4.orig/drivers/hwmon/lm73.c     2011-07-22 04:17:23.000000000 +0200
+++ linux-3.1-rc4/drivers/hwmon/lm73.c  2011-08-30 21:13:46.000000000 +0200
@@ -150,17 +150,31 @@ static int lm73_detect(struct i2c_client
                       struct i2c_board_info *info)
 {
       struct i2c_adapter *adapter = new_client->adapter;
-       u16 id;
-       u8 ctrl;
+       int id, ctrl, conf;

       if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA |
                                       I2C_FUNC_SMBUS_WORD_DATA))
               return -ENODEV;

+       /*
+        * Do as much detection as possible with byte reads first, as word
+        * reads can confuse other devices.
+        */
+       ctrl = i2c_smbus_read_byte_data(new_client, LM73_REG_CTRL);
+       if (ctrl < 0 || (ctrl & 0x10))
+               return -ENODEV;
+
+       conf = i2c_smbus_read_byte_data(new_client, LM73_REG_CONF);
+       if (conf < 0 || (conf & 0x0c))
+               return -ENODEV;
+
+       id = i2c_smbus_read_byte_data(new_client, LM73_REG_ID);
+       if (id < 0 || id != (LM73_ID & 0xff))
+               return -ENODEV;
+
       /* Check device ID */
       id = i2c_smbus_read_word_data(new_client, LM73_REG_ID);
-       ctrl = i2c_smbus_read_byte_data(new_client, LM73_REG_CTRL);
-       if ((id != LM73_ID) || (ctrl & 0x10))
+       if (id < 0 || id != LM73_ID)
               return -ENODEV;

       strlcpy(info->type, "lm73", I2C_NAME_SIZE);


--
Jean Delvare

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