[Intel-gfx] [PATCH 09/18] drm/i915: make PM interrupt writes non-destructive

[Chris Wilson]

On Tue,  6 Nov 2012 16:25:33 +0000, Ben Widawsky <ben at bwidawsk.net> wrote:
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 8f15616..5477454 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -2354,7 +2354,7 @@ static void gen6_disable_rps(struct drm_device *dev)
>  	I915_WRITE(GEN6_RC_CONTROL, 0);
>  	I915_WRITE(GEN6_RPNSWREQ, 1 << 31);
>  	I915_WRITE(GEN6_PMINTRMSK, 0xffffffff);
> -	I915_WRITE(GEN6_PMIER, 0);
> +	I915_WRITE(GEN6_PMIER, I915_READ(GEN6_PMIER) & ~GEN6_PM_RPS_EVENTS);
>  	/* Complete PM interrupt masking here doesn't race with the rps work
>  	 * item again unmasking PM interrupts because that is using a different
>  	 * register (PMIMR) to mask PM interrupts. The only risk is in leaving
> @@ -2364,7 +2364,7 @@ static void gen6_disable_rps(struct drm_device *dev)
>  	dev_priv->rps.pm_iir = 0;
>  	spin_unlock_irq(&dev_priv->rps.lock);
>  
> -	I915_WRITE(GEN6_PMIIR, I915_READ(GEN6_PMIIR));
> +	I915_WRITE(GEN6_PMIIR, I915_READ(GEN6_PMIIR) & ~GEN6_PM_RPS_EVENTS);
>  }
>  
>  int intel_enable_rc6(const struct drm_device *dev)
> @@ -2518,10 +2518,10 @@ static void gen6_enable_rps(struct drm_device *dev)
>  	gen6_set_rps(dev_priv->dev, (gt_perf_status & 0xff00) >> 8);
>  
>  	/* requires MSI enabled */
> -	I915_WRITE(GEN6_PMIER, GEN6_PM_DEFERRED_EVENTS);
> +	I915_WRITE(GEN6_PMIER, I915_READ(GEN6_PMIER) | GEN6_PM_RPS_EVENTS);
>  	spin_lock_irq(&dev_priv->rps.lock);
>  	WARN_ON(dev_priv->rps.pm_iir != 0);
> -	I915_WRITE(GEN6_PMIMR, 0);
> +	I915_WRITE(GEN6_PMIIR, I915_READ(GEN6_PMIIR) & GEN6_PM_RPS_EVENTS);
>  	spin_unlock_irq(&dev_priv->rps.lock);
>  	/* enable all PM interrupts */
>  	I915_WRITE(GEN6_PMINTRMSK, 0);

Totally confused.

IER = IER & ~RPS // only disable the RPS events
IIR = IIR & RPS // clear the asserted RPS bits

IMR != IIR.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre