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

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Message-ID: <20151123082011.GG3098@x1>
Date:	Mon, 23 Nov 2015 08:20:11 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Guenter Roeck <linux@...ck-us.net>, 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 Sat, 21 Nov 2015, Arnd Bergmann wrote:

> 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.

Works for me.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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