From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chris Wilson <chris@chris-wilson.co.uk>
Subject: Re: [PATCH 08/16] drm/i915/i2c: Convert from using
	GMBUS1 + reg_offset idiom to reg + 0
Date: Fri, 13 May 2011 10:28:34 +0100
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To: Keith Packard <keithp@keithp.com>
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On Thu, 12 May 2011 17:40:42 -0700, Keith Packard <keithp@keithp.com> wrote:
> On Thu, 12 May 2011 22:17:16 +0100, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> 
> > Keith complained that GMBUSx + reg_offset was ugly. An alternative
> > naming scheme which is more consistent with the reset of the code base
> > is to store the address of the GMBUS0 and then reference each of the
> > GMBUSx registers as an offset from GMBUS0.
> 
> This looks completely wrong -- GMBUS1 is GMBUS0 + 4, not GMBUS0 + 1.

That was shameful.

> How about a simple function that computes the GMBUS register address
> based on the device and a number? like:
> 
> static int intel_gmbus_reg(struct drm_device *dev, int reg) {
>         int     base = HAS_PCH_SPLIT(dev) ? PCH_GMBUS0 : GMBUS0;
> 
>         return base + reg * 4;

And how about something like:

#define I915_GMBUS_WRITE(reg, val) \
   I915_WRITE(intel_gmbus_reg(dev_priv->dev, reg), val)

I915_GMBUS_WRITE(0, val);

For the body?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre