Re: [PATCH] drm/i915: Skip PIPESTAT reads from irq handler on VLV/CHV when power well is down

[Imre Deak <imre.deak@intel.com>]

On to, 2016-02-18 at 21:54 +0200, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> PIPESTAT registers live in the display power well on VLV/CHV, so we
> shouldn't access them when things are powered down. Let's check
> whether the display interrupts are on or off before accessing the
> PIPESTAT registers.
> 
> Another option would be to read the PIPESTAT registers only when
> the IIR register indicates that there's a pending pipe event. But
> that would mean we might miss even more underrun reports than we
> do now, because the underrun status bit lives in PIPESTAT but doesn't
> actually generate an interrupt.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93738
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Imre Deak <imre.deak@intel.com>

Btw, I think gen8_de_irq_handler would need to be fixed too for example
by using display_irqs_enabled there as well.

> ---
>  drivers/gpu/drm/i915/i915_irq.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_irq.c
> b/drivers/gpu/drm/i915/i915_irq.c
> index 25a89373df63..d56c261ad867 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -1651,6 +1651,12 @@ static void
> valleyview_pipestat_irq_handler(struct drm_device *dev, u32 iir)
>  	int pipe;
>  
>  	spin_lock(&dev_priv->irq_lock);
> +
> +	if (!dev_priv->display_irqs_enabled) {
> +		spin_unlock(&dev_priv->irq_lock);
> +		return;
> +	}
> +
>  	for_each_pipe(dev_priv, pipe) {
>  		i915_reg_t reg;
>  		u32 mask, iir_bit = 0;
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