linux-kernel - [PATCH] drm/i915: Only run execlist context-switch handler after an interrupt

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Message-Id: <20170123155727.5841-1-chris@chris-wilson.co.uk>
Date:   Mon, 23 Jan 2017 15:57:27 +0000
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     linux-kernel@...r.kernel.org, axboe@...nel.dk
Cc:     tglx@...utronix.de, hare@...e.com, bhelgaas@...gle.com,
        glider@...gle.com, Chris Wilson <chris@...is-wilson.co.uk>
Subject: [PATCH] drm/i915: Only run execlist context-switch handler after an interrupt

Mark when we run the execlist tasklet following the interrupt, so we
don't probe a potentially uninitialised register when submitting the
contexts multiple times before the hardware responds.

Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_irq.c         | 7 +++++--
 drivers/gpu/drm/i915/intel_lrc.c        | 3 ++-
 drivers/gpu/drm/i915/intel_ringbuffer.h | 1 +
 3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 6fefc34ef602..42be116dd33d 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1349,8 +1349,11 @@ gen8_cs_irq_handler(struct intel_engine_cs *engine, u32 iir, int test_shift)
 {
 	if (iir & (GT_RENDER_USER_INTERRUPT << test_shift))
 		notify_ring(engine);
-	if (iir & (GT_CONTEXT_SWITCH_INTERRUPT << test_shift))
-		tasklet_schedule(&engine->irq_tasklet);
+
+	if (iir & (GT_CONTEXT_SWITCH_INTERRUPT << test_shift)) {
+		set_bit(IRQ_CTX_SWITCH, &engine->irq_tasklet.state);
+		tasklet_hi_schedule(&engine->irq_tasklet);
+	}
 }
 
 static irqreturn_t gen8_gt_irq_ack(struct drm_i915_private *dev_priv,
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 65bb877a726d..b55e38a590c1 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -578,7 +578,7 @@ static void intel_lrc_irq_handler(unsigned long data)
 
 	intel_uncore_forcewake_get(dev_priv, engine->fw_domains);
 
-	if (!execlists_elsp_idle(engine)) {
+	while (test_and_clear_bit(IRQ_CTX_SWITCH, &engine->irq_tasklet.state)) {
 		u32 __iomem *csb_mmio =
 			dev_priv->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_PTR(engine));
 		u32 __iomem *buf =
@@ -1347,6 +1347,7 @@ static int gen8_init_common_ring(struct intel_engine_cs *engine)
 	DRM_DEBUG_DRIVER("Execlists enabled for %s\n", engine->name);
 
 	/* After a GPU reset, we may have requests to replay */
+	clear_bit(IRQ_CTX_SWITCH, &engine->irq_tasklet.state);
 	if (!execlists_elsp_idle(engine)) {
 		engine->execlist_port[0].count = 0;
 		engine->execlist_port[1].count = 0;
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 34cdbb6350a8..c63f39d47fdd 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -373,6 +373,7 @@ struct intel_engine_cs {
 
 	/* Execlists */
 	struct tasklet_struct irq_tasklet;
+#define IRQ_CTX_SWITCH (BITS_PER_LONG - 1) /* TASKLET_STATE_USER */
 	struct execlist_port {
 		struct drm_i915_gem_request *request;
 		unsigned int count;
-- 
2.11.0