Re: [PATCH 5/5] drm/i915/gmbus: Reset the controller on initialisation

[Chris Wilson <chris@chris-wilson.co.uk>]

On Tue, 05 Apr 2011 13:59:58 -0700, Keith Packard <keithp@keithp.com> wrote:
> On Tue,  5 Apr 2011 10:24:18 +0100, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> > Toggle the Software Clear Interrupt bit which resets the controller to
> > clear any prior BUS_ERROR condition before we begin to use the
> > controller in earnest.
> 
> We do this in two places now, do we want to share the code?
> 
> > +	int reg_offset;
> > +
> > +	reg_offset = 0;
> >  	if (HAS_PCH_SPLIT(dev))
> > -		I915_WRITE(PCH_GMBUS0, 0);
> > -	else
> > -		I915_WRITE(GMBUS0, 0);
> > +		reg_offset = PCH_GMBUS0 - GMBUS0;
> > +
> > +	/* First reset the controller by toggling the Sw Clear Interrupt. */
> > +	I915_WRITE(GMBUS1 + reg_offset, GMBUS_SW_CLR_INT);
> > +	I915_WRITE(GMBUS1 + reg_offset, 0);
> > +
> > +	/* Then mark the controller as disabled. */
> > +	I915_WRITE(GMBUS0 + reg_offset, 0);
> 
> That's really ugly register addressing, but it looks like a common idiom
> in this file...

I'd change the lot for a cleaner method, the best I thought of was a
change of names for the constants/variables.

IMO,

static void i915_gmbus_write(struct drm_device *dev, int reg, int value)
{
	struct drm_i915_private *dev_priv = dev->dev_private;
	I915_WRITE(reg + (HAS_PCH_SPLIT(dev) ? PCH_GMBUS0 : GMBUS0), value);
}

expands to something dreadful.

But with a

#define GMBUS_WRITE(reg, value) i915_gmbus_write(dev, reg, value)

we go from 

  I915_WRITE(GMBUS0 + reg_offset, 0);

to

  GMBUS_WRITE(0, 0);

I would still prefer GMBUS_WRITE(GMBUS0, 0); though.

As the patch only addresses a theoretical bug, we can punt the meat of the
patch till later and attack the stylistic points first. (Obviously through
-next.)
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre