linux-kernel - Re: [RFC PATCH] Add bridge driver to connect sensors to CIO2 device via software nodes on ACPI platforms

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Date:   Fri, 18 Sep 2020 09:40:43 +0300
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Daniel Scally <djrscally@...il.com>, devel@...verdev.osuosl.org,
        robh@...nel.org, andriy.shevchenko@...ux.intel.com,
        jorhand@...ux.microsoft.com, linux-media@...r.kernel.org,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        kieran.bingham@...asonboard.com, kitakar@...il.com,
        bingbu.cao@...el.com, mchehab@...nel.org, davem@...emloft.net,
        tian.shu.qiu@...el.com, yong.zhi@...el.com
Subject: Re: [RFC PATCH] Add bridge driver to connect sensors to CIO2 device
 via software nodes on ACPI platforms

Hi Dan,

On Thu, Sep 17, 2020 at 01:49:41PM +0300, Dan Carpenter wrote:
> On Thu, Sep 17, 2020 at 01:33:43PM +0300, Sakari Ailus wrote:
> > > +static int connect_supported_devices(void)
> > > +{
> > > +	struct acpi_device *adev;
> > > +	struct device *dev;
> > > +	struct sensor_bios_data ssdb;
> > > +	struct sensor *sensor;
> > > +	struct property_entry *sensor_props;
> > > +	struct property_entry *cio2_props;
> > > +	struct fwnode_handle *fwnode;
> > > +	struct software_node *nodes;
> > > +	struct v4l2_subdev *sd;
> > > +	int i, ret;
> > 
> > unsigned int i
> > 
> 
> Why?
> 
> For list iterators then "int i;" is best...  For sizes then unsigned is
> sometimes best.  Or if it's part of the hardware spec or network spec
> unsigned is best.  Otherwise unsigned variables cause a ton of bugs.
> They're not as intuitive as signed variables.  Imagine if there is an
> error in this loop and you want to unwind.  With a signed variable you
> can do:
> 
> 	while (--i >= 0)
> 		cleanup(&bridge.sensors[i]);
> 
> There are very few times where raising the type maximum from 2 billion
> to 4 billion fixes anything.

There's simply no need for the negative integers here. Sizes (as it's a
size here) are unsigned, too, so you'd be comparing signed and unsigned
numbers later in the function.

-- 
Regards,

Sakari Ailus