[Intel-gfx] [PATCH 2/8] drm/i915: don't disable/reenable IVB error interrupts when not needed

[Chris Wilson]

On Mon, Jul 29, 2013 at 05:48:21PM -0300, Paulo Zanoni wrote:
> From: Paulo Zanoni <paulo.r.zanoni at intel.com>
> 
> If the error interrupts are already disabled, don't disable and
> reenable them. This is going to be needed when we're in PC8+, where
> all the interrupts are disabled so we won't risk re-enabling
> DE_ERR_INT_IVB.

>  	if (IS_HASWELL(dev)) {
>  		spin_lock(&dev_priv->irq_lock);
> -		ironlake_disable_display_irq(dev_priv, DE_ERR_INT_IVB);
> +		if (!(I915_READ(DEIMR) & DE_ERR_INT_IVB)) {
> +			ironlake_disable_display_irq(dev_priv, DE_ERR_INT_IVB);
> +			err_int_reenable = true;
> +		}

Or just make ironlake_disable_display_irq() return a bool. So this then
raises the question: please justify why the deimr state tracker is out
of sync with the register. If it is possible that we write to this
register whilst under pc8 and then restore a different value, that is
scary. I would rather have a big BUG_ON(!pc8) inside
ironlake_disable_display_irq() and move the pc8 handling logic there
(i.e. if we get a request for something whilst under pc8, modify the
saved bits rather than the actual register).
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre