[Intel-gfx] [PATCH 13/13] drm/i915: Use binary search when looking for shadowed registers

[Joonas Lahtinen]

On to, 2016-09-29 at 16:35 +0100, Tvrtko Ursulin wrote:
> +static int mmio_reg_cmp(const void *key, const void *elt)
+ {
<SNIP>
> 
> +	if (offset < i915_mmio_reg_offset(*reg))
> +		return -1;
> +	else if (offset > i915_mmio_reg_offset(*reg))
> +		return 1;
> +	else
> +		return 0;

I was about to suggest return a - b; but then realized it might
overflow. After a bit of searching, that is done in
regcache_default_cmp though. So not sure if it's a bug in there or did
I miss something. This is safe way at least.

>  static bool is_gen8_shadowed(u32 offset)
>  {
> > -	int i;
> > -	for (i = 0; i < ARRAY_SIZE(gen8_shadowed_regs); i++)
> > -		if (offset == gen8_shadowed_regs[i].reg)
> > -			return true;
> > +	i915_reg_t *reg;
>  
> > -	return false;
> +	reg = bsearch((void *)(unsigned long)offset,

(unsigned long) is not required, as we don't have sign bits to extend.

> +		      (const void *)gen8_shadowed_regs,
> +		      ARRAY_SIZE(gen8_shadowed_regs),
> +		      sizeof(i915_reg_t),
> +		      mmio_reg_cmp);
> +
> +	return reg ? true : false;

As I previously learnt, no need to explicitly convert bool types
anymore, so this can just be return bsearch(...);

With the last two fixed,

Reviewed-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation