[Intel-gfx] [PATCH v2 2/5] drm/i915: Only run execlist context-switch handler after an interrupt

[Mika Kuoppala]

Chris Wilson <chris at chris-wilson.co.uk> writes:

> Mark when we run the execlist tasklet following the interrupt, so we
> don't probe a potentially initialised register when submitting the
> contexts multiple times.
>
> Signed-off-by: Chris Wilson <chris at chris-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 873c3a8a580b..d2adfc77260a 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -577,7 +577,7 @@ 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 =
> @@ -1346,6 +1346,7 @@ 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 */

Looking at the tasklet code, TASKLET_STATE_USER would be a
good idea. However until we have one, I think we need to
avoid piggybacking on tasklet state.

-Mika

>  	struct execlist_port {
>  		struct drm_i915_gem_request *request;
>  		unsigned int count;
> -- 
> 2.11.0