linux-kernel - Re: [PATCH v3 2/5] mfd: syscon: add a DT property to set value width

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Date:	Sat, 21 Nov 2015 00:13:27 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Guenter Roeck <linux@...ck-us.net>,
	Lee Jones <lee.jones@...aro.org>, dinh.linux@...il.com,
	linux-watchdog@...r.kernel.org,
	Damien Riegel <damien.riegel@...oirfairelinux.com>,
	linux-kernel@...r.kernel.org, wim@...ana.be, robh+dt@...nel.org,
	kernel@...oirfairelinux.com, kernel@...gutronix.de,
	shawnguo@...nel.org, sameo@...ux.intel.com
Subject: Re: [PATCH v3 2/5] mfd: syscon: add a DT property to set value width

On Tuesday 17 November 2015 09:26:49 Guenter Roeck wrote:
> > 
> > This syntax is confusing, as we normally associate it with an error
> > condition.  Instead, I'd use:
> > 
> >   if (of_property_read_u32(np, "bus-width", &bus_width) == 0)
> 
> Or maybe better
> 
>         if (!of_property_read_u32(np, "bus-width", &bus_width))

I would also prefer the latter, but it doesn't matter much either way.

> > 
> > Or, for more clarity:
> > 
> >   of_property_read_u32(np, "bus-width", &bus_width);
> >   if (bus_width)
> > 
> > If you choose this version (which I think is my preferred method, don't
> > forget to initialise 'bus_width' to zero.
> > 
> Ignoring an error and depending on bus_width==0 to determine if the property
> was provided seems odd, especially since it would "hide" if the bus-width
> property is set to 0. In the original code, this would be detected as error.

Right.

Another option would be

	ret = of_property_read_u32(np, "bus-width", &bus_width);
	/* no bus width provided, default to 32-bit */
	if (ret)
		bus_width = 32;

	syscon_config.val_bits = bus_width;
	syscon_config.reg_stride = syscon_config.val_bits / 8;

which has the same effect but seems a little clearer to me.

	Arnd
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