From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Thu, 28 Jun 2018 21:12:03 +0100
Subject: drm/i915: Drop posting reads to flush master interrupts
Git-commit: 74093f3eccac232447ef95536c6a359ee7661650
Patch-mainline: v4.19-rc1
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166
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: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ville Syrjala <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180628201211.13837-1-chris@chris-wilson.co.uk
Acked-by: Petr Tesarik <ptesarik@suse.com>
---
drivers/gpu/drm/i915/i915_irq.c | 9 +--------
1 file changed, 1 insertion(+), 8 deletions(-)
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -2211,7 +2211,6 @@ static irqreturn_t valleyview_irq_handle
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);
@@ -2296,7 +2295,6 @@ static irqreturn_t cherryview_irq_handle
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);
@@ -2665,7 +2663,6 @@ static irqreturn_t ironlake_irq_handler(
/* 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
@@ -2675,7 +2672,6 @@ static irqreturn_t ironlake_irq_handler(
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 */
@@ -2710,11 +2706,8 @@ static irqreturn_t ironlake_irq_handler(
}
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);