linux-kernel - Re: [PATCH v4 1/3] mfd: tps6586x: add version detection

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20131206084453.GB13093@lee--X1>
Date:	Fri, 6 Dec 2013 08:44:53 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Stefan Agner <stefan@...er.ch>
Cc:	Stephen Warren <swarren@...dotorg.org>, thierry.reding@...il.com,
	dev@...xeye.de, lgirdwood@...il.com, broonie@...nel.org,
	kai.poggensee@...onic-design.de, sameo@...ux.intel.com,
	linux-tegra@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/3] mfd: tps6586x: add version detection

> >> <snip>
> >>>> @@ -493,13 +527,12 @@ static int tps6586x_i2c_probe(struct i2c_client *client,
> >>>>  		return -EIO;
> >>>>  	}
> >>>>
> >>>> -	dev_info(&client->dev, "VERSIONCRC is %02x\n", ret);
> >>>> -
> >>>>  	tps6586x = devm_kzalloc(&client->dev, sizeof(*tps6586x), GFP_KERNEL);
> >>>> -	if (tps6586x == NULL) {
> >>>> -		dev_err(&client->dev, "memory for tps6586x alloc failed\n");
> >>>> +	if (!tps6586x)
> >>>>  		return -ENOMEM;
> >>>> -	}
> >>>> +
> >>>> +	tps6586x->version = ret;
> >>>
> >>> I have to say, I dislike this version of the patch. Separating the
> >>> reading of the version register from the assignment to tps6586x->version
> >>> doesn't make any sense, especially given that the version value is
> >>> stored in a variable named "ret"; that name isn't remotely related to
> >>> what's stored there. What if someone comes along later and adds more
> >>> code that assigns to ret between where it's repurposed for the version
> >>> value and where it's assigned to tps6586x->version? It'd be extremely
> >>> difficult for a patch reviewer to spot that given the limited context in
> >>> a diff, and quite non-obvious to the person changing the code too..
> >>
> >> The value comes from the return value of i2c_smbus_read_byte_data. If
> >> the value is below zero its an EIO error.
> >>
> >> I could add a variable "version", but for me it felt strange because we
> >> check if version is below zero. This feels like its a wrong version
> >> rather than a transmit error. So I would prefer ret over version. But I
> >> agree, when one just reads the patch, its not obvious what exactly
> >> happens.
> > 
> > In my opinion, using a variable named "version" here would be
> > preferable. Testing that against <0 is just the way the I2C API works,
> > so the same argument could be applied to any I2C access.

So, FWIW I agree with Stephen and have done from the start. Please
see my original comment from the first submission:

> >       ret = i2c_smbus_read_byte_data(client, TPS6586X_VERSIONCRC);
>   If you're going to do this, please change 'ret' to 'version'.

> Hm, I try the empiric way:
> 
> $ grep -r -e i2c_smbus_read_byte_data | grep "ret =" | wc -l
> 139
> $ grep -r -e i2c_smbus_read_byte_data | grep "version =" | wc -l
> 3
> 
> Ok, thats not fair at all, version is usage specific whilst ret is not.
> 
> $ grep -r -e i2c_smbus_read_byte_data | grep " = " | wc -l
> 703

I not really that worried about what everyone else does. I'm more
concerned with doing what we deem to be the correct thing here.

> On the other hand is the additional variable. But I think the compiler
> will optimize that anyway, so this might not be an argument at all :-)
> 
> I see your point... Should I create another patch revision? Lee, is the
> patch already merged?

It isn't. Please submit another version as Stephen requests.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/