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Commit 74093f3e authored by Chris Wilson's avatar Chris Wilson
Browse files

drm/i915: Drop posting reads to flush master interrupts 



We do not need to do a posting read of our uncached mmio write to
re-enable the master interrupt lines after handling an interrupt, so
don't. This saves us a slow UC read before we can process the interrupt,
most noticeable in execlists where any stalls imposes extra latency on
GPU command execution.

Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: default avatarVille Syrjala <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180628201211.13837-1-chris@chris-wilson.co.uk
parent f7dc0157

drivers/gpu/drm/i915/i915_irq.c

+1 −8
Original line number Diff line number Diff line
@@ -2183,7 +2183,6 @@ static irqreturn_t valleyview_irq_handler(int irq, void *arg) 


		I915_WRITE(VLV_IER, ier);

		I915_WRITE(VLV_MASTER_IER, MASTER_INTERRUPT_ENABLE);

		POSTING_READ(VLV_MASTER_IER);



		if (gt_iir)

			snb_gt_irq_handler(dev_priv, gt_iir);
@@ -2268,7 +2267,6 @@ static irqreturn_t cherryview_irq_handler(int irq, void *arg) 


		I915_WRITE(VLV_IER, ier);

		I915_WRITE(GEN8_MASTER_IRQ, GEN8_MASTER_IRQ_CONTROL);

		POSTING_READ(GEN8_MASTER_IRQ);



		gen8_gt_irq_handler(dev_priv, master_ctl, gt_iir);
@@ -2637,7 +2635,6 @@ static irqreturn_t ironlake_irq_handler(int irq, void *arg) 
	/* disable master interrupt before clearing iir  */

	de_ier = I915_READ(DEIER);

	I915_WRITE(DEIER, de_ier & ~DE_MASTER_IRQ_CONTROL);

	POSTING_READ(DEIER);



	/* Disable south interrupts. We'll only write to SDEIIR once, so further

	 * interrupts will will be stored on its back queue, and then we'll be
@@ -2647,7 +2644,6 @@ static irqreturn_t ironlake_irq_handler(int irq, void *arg) 
	if (!HAS_PCH_NOP(dev_priv)) {

		sde_ier = I915_READ(SDEIER);

		I915_WRITE(SDEIER, 0);

		POSTING_READ(SDEIER);

	}



	/* Find, clear, then process each source of interrupt */
@@ -2682,11 +2678,8 @@ static irqreturn_t ironlake_irq_handler(int irq, void *arg) 
	}



	I915_WRITE(DEIER, de_ier);

	POSTING_READ(DEIER);

	if (!HAS_PCH_NOP(dev_priv)) {

	if (!HAS_PCH_NOP(dev_priv))

		I915_WRITE(SDEIER, sde_ier);

		POSTING_READ(SDEIER);

	}



	/* IRQs are synced during runtime_suspend, we don't require a wakeref */

	enable_rpm_wakeref_asserts(dev_priv);