linux-kernel - Re: [PATCH 3/13 v2] viafb: accel.c, accel.h

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Date:	Tue, 19 Aug 2008 16:23:03 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	<JosephChan@....com.tw>
Cc:	JosephChan@....com.tw, linux-fbdev-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, geert@...ux-m68k.org
Subject: Re: [PATCH 3/13 v2] viafb: accel.c, accel.h

On Fri, 8 Aug 2008 18:11:05 +0800
<JosephChan@....com.tw> wrote:

> 2D and HW cursor stuff of viafb driver.

x86_64 allmodconfig throws a lot of warnings:

drivers/video/via/viafbdev.c: In function 'viafb_fillrect':
drivers/video/via/viafbdev.c:904: warning: cast from pointer to integer of different size
drivers/video/via/viafbdev.c:904: warning: cast from pointer to integer of different size
drivers/video/via/viafbdev.c: In function 'viafb_copyarea':
drivers/video/via/viafbdev.c:955: warning: cast from pointer to integer of different size
drivers/video/via/viafbdev.c:955: warning: cast from pointer to integer of different size
drivers/video/via/viafbdev.c:959: warning: cast from pointer to integer of different size
drivers/video/via/viafbdev.c:959: warning: cast from pointer to integer of different size
drivers/video/via/viafbdev.c: In function 'viafb_imageblit':
drivers/video/via/viafbdev.c:1016: warning: cast from pointer to integer of different size
drivers/video/via/viafbdev.c:1016: warning: cast from pointer to integer of different size
drivers/video/via/viafbdev.c: In function 'via_pci_probe':
drivers/video/via/viafbdev.c:2119: warning: cast from pointer to integer of different size
drivers/video/via/viafbdev.c:2119: warning: cast to pointer from integer of different size
drivers/video/via/viafbdev.c:2121: warning: cast from pointer to integer of different size
drivers/video/via/viafbdev.c:2121: warning: cast to pointer from integer of different size
drivers/video/via/viafbdev.c:2123: warning: cast from pointer to integer of different size
drivers/video/via/viafbdev.c:2123: warning: cast to pointer from integer of different size
drivers/video/via/viafbdev.c:2125: warning: cast from pointer to integer of different size
drivers/video/via/viafbdev.c:2125: warning: cast to pointer from integer of different size
drivers/video/via/viafbdev.c:2127: warning: cast from pointer to integer of different size
drivers/video/via/viafbdev.c:2127: warning: cast to pointer from integer of different size

due to things like this:

        MMIO_OUT32(VIA_REG_DSTBASE,
                   ((u32) (info->screen_base) - (u32) viafb_FB_MM) >> 3);

now, we could just shut the warnings up by casting to (long) instead.

But I wonder what's going on in there.  ->screen_base came from
ioremap_nocache() and AFAIK there's no guarantee that this virtual
address will be less than 4G on 64-bit machines?



Also, from a stylistic point ov view, this:

#define VIA_MMIO 1

#if VIA_MMIO
#define MMIO_OUT32(reg, val) writel(val, viaparinfo->io_virt + reg)
#define MMIO_IN32(reg)      readl(viaparinfo->io_virt + reg)

#else
#define MMIO_OUT32(reg, val) outl(val, reg)
#define MMIO_IN32(reg)      inl(reg)
#endif

is quite ugly.

If the !VIA_MMIO code has no valid use then please just remove it.

The VIA_MMIO!=0 macros inplicitly reference a local variable which is
the kind of dopey programming trick which should not be performed in
new code.  It would be much better to do

static inline void via_writel(struct viafb_par *viaparinfo, int reg, u32 val)
{
	writel(val, viaparinfo->io_virt + reg);
}

and use that everywhere.

It would also be quite acceptable to simply open-code the

	writel(val, viaparinfo->io_virt + reg);

at all callsites.

Those macros may have made it easier to _write_ the code, but they make
it harder to _read_ it.  That's a wrong tradeoff.


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