linux-kernel - Re: [PATCH 1/3] platform: add common resource requesting and mapping helper

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Message-ID: <20120131203455.GG22611@ponder.secretlab.ca>
Date:	Tue, 31 Jan 2012 13:34:55 -0700
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Wolfram Sang <w.sang@...gutronix.de>
Cc:	Barry Song <21cnbao@...il.com>, Barry Song <Barry.Song@....com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	linux-kernel@...r.kernel.org, workgroup.linux@....com,
	Erik Gilling <konkers@...gle.com>,
	linux-mtd@...ts.infradead.org, Barry Song <Baohua.Song@....com>,
	David Woodhouse <dwmw2@...radead.org>,
	Atsushi Nemoto <anemo@....ocn.ne.jp>
Subject: Re: [PATCH 1/3] platform: add common resource requesting and mapping
 helper

On Tue, Jan 31, 2012 at 12:33:58PM +0100, Wolfram Sang wrote:
> Barry,
> 
> > > You don't need to do the error checking for 'res'. You can simply do
> > >
> > > res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > > base = devm_request_and_ioremap(&dev->dev, res);
> > 
> > i do know  devm_request_and_ioremap() does res checking. but that is
> > implicit, confused and not a smart way actually.
> 
> I agree about the implicit thing (keep in mind the function is new). But
> calling a function "not smart" because it checks its arguments? I do
> like the NULL check of kfree() for example.
> 
> > actually, no people by now really use the implicit checking. that
> > shows people don't really think that is a good programming way.
> 
> I'd think most people just copy&paste and don't have an opinion either
> way, so the quantity doesn't show much.
> 
> > > devm_request_and_ioremap() will check res. Given that, I don't think
> > > we can save a lot with another wrapper.
> > 
> > i think we can save some.
> > The story begins from Grant's feedback in:
> > http://www.spinics.net/lists/arm-kernel/msg157644.html
> 
> I am not sure using 'platform_devm_request_and_ioremap' and later using
> plain 'devm_*' functions (without platform_-prefix) is less confusing.
> The alternative would be to check which helper functions also use
> 'struct resource' and if they do checks on that. If all do that, you
> would have the simple rule, that you only need to check yourself if you
> access it yourself.

The reason I suggested the wrapper is that then the driver code doesn't need
to fart around with the res pointer at all.  It reduces boilerplate in platform
drivers which I think is a good thing.

g.

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