linux-kernel - Re: [PATCH 1/6] gxfb: create DC/VP/FP-specific handlers rather than using readl/writel

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Message-Id: <20080310144842.593d1b80.akpm@linux-foundation.org>
Date:	Mon, 10 Mar 2008 14:48:42 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andres Salomon <dilinger@...ued.net>
Cc:	adaplas@...il.com, linux-kernel@...r.kernel.org,
	linux-fbdev-devel@...ts.sourceforge.net, info-linux@...de.amd.com,
	jordan.crouse@....com
Subject: Re: [PATCH 1/6] gxfb: create DC/VP/FP-specific handlers rather than
 using readl/writel

On Mon, 10 Mar 2008 17:35:44 -0400
Andres Salomon <dilinger@...ued.net> wrote:

> On Mon, 10 Mar 2008 14:24:05 -0700
> Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > On Sat, 8 Mar 2008 20:48:26 -0500
> > Andres Salomon <dilinger@...ued.net> wrote:
> > 
> > > +#define read_dc(reg)		readl(par->dc_regs + (reg))
> > > +#define write_dc(reg, val)	writel((val), par->dc_regs + (reg))
> > > +
> > > +#define read_vp(reg)		readl(par->vid_regs + (reg))
> > > +#define write_vp(reg, val)	writel((uint32_t) (val), \
> > > +					par->vid_regs + (reg))
> > > +
> > > +#define read_fp(reg)		readl(par->vid_regs + (reg))
> > > +#define write_fp(reg, val)	writel((uint32_t) (val), \
> > > +					par->vid_regs + (reg))
> > > +
> > 
> > Not very nice, sorry.  They're macros, and macros rather suck.  And they
> > implicitly rely upon the caller having some variable called "par" in scope.
> > 
> > It would be much nicer to do
> > 
> > /*
> >  * documentation goes here
> >  */
> > static inline u32 read_dc(struct geodefb_par *par, int reg)
> > {
> > 	return readl(par->dc_regs, reg);
> > }
> > 
> > no?
> 
> I can change it if you'd like (although.. sigh.)
> 
> However, it's a lot of extra passing around of the 'par' without any
> good reason.  Normal I prefer inline functions to macros as well, but
> I don't see the point here.
>  

It'll generate the same (or similar) code in both versions.

Code is written once and is read thousands of times, so we should optimise
for readers, not writers.  And I do think that being conventional here
helps readability, even if it does add a bit more source code.

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