Re: [Intel-gfx] [PATCH 1/2] drm/i915/gt: Don't do display work on platforms without display

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 10 Oct 2022, Ashutosh Dixit <ashutosh.dixit@intel.com> wrote:
> Do display work only on platforms with display. This avoids holding the
> runtime PM wakeref for an additional 100+ ms after GT has been parked.
>
> Bug: https://gitlab.freedesktop.org/drm/intel/-/issues/7025
> Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
> ---
>  drivers/gpu/drm/i915/gt/intel_gt_pm.c | 36 +++++++++++++++------------
>  1 file changed, 20 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_pm.c b/drivers/gpu/drm/i915/gt/intel_gt_pm.c
> index f553e2173bdad..26aa2e979a148 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gt_pm.c
> +++ b/drivers/gpu/drm/i915/gt/intel_gt_pm.c
> @@ -70,19 +70,21 @@ static int __gt_unpark(struct intel_wakeref *wf)
>  
>  	GT_TRACE(gt, "\n");
>  
> -	/*
> -	 * It seems that the DMC likes to transition between the DC states a lot
> -	 * when there are no connected displays (no active power domains) during
> -	 * command submission.
> -	 *
> -	 * This activity has negative impact on the performance of the chip with
> -	 * huge latencies observed in the interrupt handler and elsewhere.
> -	 *
> -	 * Work around it by grabbing a GT IRQ power domain whilst there is any
> -	 * GT activity, preventing any DC state transitions.
> -	 */
> -	gt->awake = intel_display_power_get(i915, POWER_DOMAIN_GT_IRQ);
> -	GEM_BUG_ON(!gt->awake);
> +	if (HAS_DISPLAY(i915) && INTEL_DISPLAY_ENABLED(i915)) {

Feels like something's wrong if you need both of those.

BR,
Jani.

> +		/*
> +		 * It seems that the DMC likes to transition between the DC states a lot
> +		 * when there are no connected displays (no active power domains) during
> +		 * command submission.
> +		 *
> +		 * This activity has negative impact on the performance of the chip with
> +		 * huge latencies observed in the interrupt handler and elsewhere.
> +		 *
> +		 * Work around it by grabbing a GT IRQ power domain whilst there is any
> +		 * GT activity, preventing any DC state transitions.
> +		 */
> +		gt->awake = intel_display_power_get(i915, POWER_DOMAIN_GT_IRQ);
> +		GEM_BUG_ON(!gt->awake);
> +	}
>  
>  	intel_rc6_unpark(&gt->rc6);
>  	intel_rps_unpark(&gt->rps);
> @@ -115,9 +117,11 @@ static int __gt_park(struct intel_wakeref *wf)
>  	/* Everything switched off, flush any residual interrupt just in case */
>  	intel_synchronize_irq(i915);
>  
> -	/* Defer dropping the display power well for 100ms, it's slow! */
> -	GEM_BUG_ON(!wakeref);
> -	intel_display_power_put_async(i915, POWER_DOMAIN_GT_IRQ, wakeref);
> +	if (HAS_DISPLAY(i915) && INTEL_DISPLAY_ENABLED(i915)) {
> +		/* Defer dropping the display power well for 100ms, it's slow! */
> +		GEM_BUG_ON(!wakeref);
> +		intel_display_power_put_async(i915, POWER_DOMAIN_GT_IRQ, wakeref);
> +	}
>  
>  	return 0;
>  }

-- 
Jani Nikula, Intel Open Source Graphics Center