linux-kernel - Re: [PATCH v2] i2c: stub: Add support for SMBus block commands

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Date:	Sun, 13 Jul 2014 08:46:41 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Jean Delvare <jdelvare@...e.de>
CC:	Wolfram Sang <wsa@...-dreams.de>,
	Randy Dunlap <rdunlap@...radead.org>,
	linux-i2c@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] i2c: stub: Add support for SMBus block commands

On 07/13/2014 08:13 AM, Jean Delvare wrote:
> On Sun, 13 Jul 2014 08:04:54 -0700, Guenter Roeck wrote:
>> On 07/13/2014 12:21 AM, Jean Delvare wrote:
>>> Hi Guenter,
>>>
>>> On Sat, 12 Jul 2014 08:05:49 -0700, Guenter Roeck wrote:
>>>> Any idea how we could inject errors ? Error path testing would be quite useful.
>>>
>>> Good idea. This should probably be done with a sysfs attribute so that
>>> it can be turned on and off as desired. Off by default, of course. Some
>>> other subsystems already support error injection, you could check how
>>> they are doing it, do that we do not diverge needlessly.
>>>
>>> Do you think there is any value in failing with different error codes,
>>> or just -EIO is enough?
>>
>> How about writing the error code to return into the attribute ?
>> Write anything negative, and it is returned as error. Write 0,
>> and the driver works as normal.
>
> This is smart, I like it :)
>
>>> Do you think it should fail all the time when error injection is
>>> enabled, or is there a value in having only a certain % of commands
>>> fail?
>>
>> For my purposes I would want it to fail reliably. We could add some fanciness,
>> though: Provide a second attribute which specifies how many operations should
>> pass before the first failure.
>
> Let's start simple and just implement what you need.
>

I would actually benefit from both. The ability to return an error unconditionally
lets me test the first error path. The ability to return an error starting with the
n-th transfer lets me test the n-th error path.

Guenter

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