[Intel-gfx] [PATCH 3/4] drm/i915: Try harder to get FBC

[Ben Widawsky]

Rodrigo, when you're ready, can you pull in Art's requests?

On Fri, Jun 20, 2014 at 03:56:08PM +0000, Runyan, Arthur J wrote:
> You give me too much credit.  I just gave you an explanation of what the hardware does, then you ran with it.
> 
> On Thu, Jun 19, 2014 at 12:06:13PM -0700, Ben Widawsky wrote:
> +		DRM_INFO("Reducing the compressed framebuffer size. This may lead to increased power. Try to increase stolen memory size if available in BIOS.\n");
> 
> I prefer "This may lead to less power savings than a non-reduced size." since FBC is still going to save power.

Got it.

> 
>  	dpfc_ctl = DPFC_CTL_PLANE(intel_crtc->plane);
>  	if (drm_format_plane_cpp(fb->pixel_format, 0) == 2)
> +		dev_priv->fbc.threshold++;
> +
> +	switch (dev_priv->fbc.threshold) {
> +	case 4:
> +		dpfc_ctl |= DPFC_CTL_LIMIT_4X;
> +		break;
> +	case 2:
>  		dpfc_ctl |= DPFC_CTL_LIMIT_2X;
> -	else
> +		break;
> +	case 1:
>  		dpfc_ctl |= DPFC_CTL_LIMIT_1X;
> +		break;
> +	}
> 
> I Am Not A Coder, but at a glance it looks like the ++ could lead to undefined case 3 when you want case 4.
> 
Thanks for your feedback. 3 is an invalid value, but a default case
should be added here. I'd do a BUG_ON, but that's strictly forbidden.

-- 
Ben Widawsky, Intel Open Source Technology Center