linux-kernel - Re: [PATCH v3 4/4] can: kvaser_usb: Add support for the Usbcan-II family

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Message-ID: <54B3BF6C.4000004@pengutronix.de>
Date:	Mon, 12 Jan 2015 13:34:52 +0100
From:	Marc Kleine-Budde <mkl@...gutronix.de>
To:	"Ahmed S. Darwish" <darwish.07@...il.com>
CC:	Olivier Sobrie <olivier@...rie.be>,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	Wolfgang Grandegger <wg@...ndegger.com>,
	"David S. Miller" <davem@...emloft.net>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Linux-CAN <linux-can@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 4/4] can: kvaser_usb: Add support for the Usbcan-II
 family

On 01/12/2015 01:26 PM, Ahmed S. Darwish wrote:
> On Mon, Jan 12, 2015 at 12:51:49PM +0100, Marc Kleine-Budde wrote:
>> On 01/08/2015 04:19 PM, Ahmed S. Darwish wrote:
>>
>> [...]
>>
>>>>>  MODULE_DEVICE_TABLE(usb, kvaser_usb_table);
>>>>> @@ -463,7 +631,18 @@ static int kvaser_usb_get_software_info(struct kvaser_usb *dev)
>>>>>  	if (err)
>>>>>  		return err;
>>>>>  
>>>>> -	dev->fw_version = le32_to_cpu(msg.u.softinfo.fw_version);
>>>>> +	switch (dev->family) {
>>>>> +	case KVASER_LEAF:
>>>>> +		dev->fw_version = le32_to_cpu(msg.u.leaf.softinfo.fw_version);
>>>>> +		break;
>>>>> +	case KVASER_USBCAN:
>>>>> +		dev->fw_version = le32_to_cpu(msg.u.usbcan.softinfo.fw_version);
>>>>> +		break;
>>>>> +	default:
>>>>> +		dev_err(dev->udev->dev.parent,
>>>>> +			"Invalid device family (%d)\n", dev->family);
>>>>> +		return -EINVAL;
>>>>
>>>> The default case should not happen. I think you can remove it.
>>
>>> It's true, it _should_ never happen. But I only add such checks if
>>> the follow-up code critically depends on a certain `dev->family`
>>> behavior. So it's kind of a defensive check against any possible
>>> bug in driver or memory.
>>>
>>> What do you think?
>>
>> The kernel is full of callback functions, if you have a bit flip there
>> you're in trouble anyways. A bug in the driver (or other parts of the
>> kernel) might overwrite the memory of dev->family, but if this happens,
>> more things will break.
>>
> 
> I see. Thanks for the explanation.
> 
> Most of them are now removed in latest submission, except two to
> avoid GCC warnings of variables that "may be used uninitialized".

Thanks, I'll look at the code later and try to figure out what gcc's
problem might be.

Marc

-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
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