linux-kernel - adm9240 error handling (was Re: [PATCHv1] hwmon: adm9240: handle temperature readings below 0)

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Message-ID: <56fa4053f8a448a38b9f1e0dd45a0092@svr-chch-ex1.atlnz.lc>
Date:   Wed, 5 Oct 2016 05:00:52 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Guenter Roeck <linux@...ck-us.net>
CC:     "jdelvare@...e.com" <jdelvare@...e.com>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Wang <Michael.Wang@...iedtelesis.co.nz>
Subject: adm9240 error handling (was Re: [PATCHv1] hwmon: adm9240: handle
 temperature readings below 0)

Hi Guenter,

On 10/05/2016 11:10 AM, Guenter Roeck wrote:
> On Tue, Oct 04, 2016 at 09:09:10PM +0000, Chris Packham wrote:
>>
>>>
>>> Of course, all that doesn't solve the real problem in this driver, which is
>>> that it ignores error codes from the smbus functions, but that is a different
>>> problem.
>>
>> Yeah I'd noted that too. This patch is actually a port of changes we've
>> made to a custom LM81 driver based on the original adm9240 driver which
>> included some error handling. I'll look at bringing more of that code in
>> for a future patch.
>>
> Sounds good...
>

So on this. The as-yet unpublished changes we have basically consist of 
changing adm9240_update_device() to do something like this

                         || !data->valid) {

                 for (i = 0; i < 6; i++) { /* read voltages */
-                       data->in[i] = i2c_smbus_read_byte_data(client,
+                       ret = i2c_smbus_read_byte_data(client,
                                         ADM9240_REG_IN(i));
+                       if (ret >= 0)
+                               data->in[i] = ret;

The user is still none the wiser that there was an error but at least we 
haven't just attempted to write a error code to the data. Is this the 
direction you want to head? Are there other hwmon drivers that do 
something saner?

Another attempt we've made is to try to read something innocuous like 
the CONFIG register to check that the i2c bus is in a good state before 
reading the rest of the values.

As you can guess these "fixes" have piled up over time and because 
they're hard to test we haven't been brave enough to remove them.

Any thoughts?