Re: [PATCH v2] drm/i915/gt: Allow clobbering gpu resets if the display is off

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Sep 11, 2019 at 11:19:59AM +0100, Chris Wilson wrote:
> If the display is inactive, we need not worry about the gpu reset
> clobbering the display! To prevent the display changing state between us
> checking the active state and doing the hard reset, we introduce the
> lightweight reset lock to the atomic commit for the affected (legacy)
> platforms.
> 
> Testcase: igt/gem_eio/kms
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_display.c | 11 +++++++++++
>  drivers/gpu/drm/i915/gt/intel_reset.c        | 18 +++++++++++++++++-
>  2 files changed, 28 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 4ee750fa3ef0..a92487d8f4cf 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -13986,6 +13986,7 @@ static void intel_atomic_commit_tail(struct intel_atomic_state *state)
>  	struct intel_crtc *crtc;
>  	u64 put_domains[I915_MAX_PIPES] = {};
>  	intel_wakeref_t wakeref = 0;
> +	int srcu;
>  	int i;
>  
>  	intel_atomic_commit_fence_wait(state);
> @@ -14005,6 +14006,12 @@ static void intel_atomic_commit_tail(struct intel_atomic_state *state)
>  		}
>  	}
>  
> +	/* Prevent starting a GPU reset while we change global display state */
> +	srcu = -ENODEV;
> +	if (INTEL_INFO(dev_priv)->gpu_reset_clobbers_display)
> +		/* only fails if interrupted */
> +		srcu = intel_gt_reset_trylock(&dev_priv->gt);

Hmm. What happens if we're holding the modeset locks and there's an
ongoing reset blocked on said locks?

> +
>  	intel_commit_modeset_disables(state);
>  
>  	/* FIXME: Eventually get rid of our crtc->config pointer */
> @@ -14049,6 +14056,10 @@ static void intel_atomic_commit_tail(struct intel_atomic_state *state)
>  	/* Now enable the clocks, plane, pipe, and connectors that we set up. */
>  	dev_priv->display.commit_modeset_enables(state);
>  
> +
> +	if (srcu > 0)
> +		intel_gt_reset_unlock(&dev_priv->gt, srcu);
> +
>  	if (state->modeset) {
>  		intel_encoders_update_complete(state);
>  
> diff --git a/drivers/gpu/drm/i915/gt/intel_reset.c b/drivers/gpu/drm/i915/gt/intel_reset.c
> index d8b1498d7ab7..df4a86bdb6f6 100644
> --- a/drivers/gpu/drm/i915/gt/intel_reset.c
> +++ b/drivers/gpu/drm/i915/gt/intel_reset.c
> @@ -7,6 +7,7 @@
>  #include <linux/sched/mm.h>
>  #include <linux/stop_machine.h>
>  
> +#include "display/intel_display.h"
>  #include "display/intel_display_types.h"
>  #include "display/intel_overlay.h"
>  
> @@ -729,6 +730,21 @@ static void nop_submit_request(struct i915_request *request)
>  	intel_engine_queue_breadcrumbs(engine);
>  }
>  
> +static bool reset_clobbers_display(struct drm_i915_private *i915)
> +{
> +	struct intel_crtc *crtc;
> +
> +	if (!INTEL_INFO(i915)->gpu_reset_clobbers_display)
> +		return false;
> +
> +	for_each_intel_crtc(&i915->drm, crtc) {
> +		if (crtc->active)
> +			return true;
> +	}
> +
> +	return false;
> +}
> +
>  static void __intel_gt_set_wedged(struct intel_gt *gt)
>  {
>  	struct intel_engine_cs *engine;
> @@ -755,7 +771,7 @@ static void __intel_gt_set_wedged(struct intel_gt *gt)
>  	awake = reset_prepare(gt);
>  
>  	/* Even if the GPU reset fails, it should still stop the engines */
> -	if (!INTEL_INFO(gt->i915)->gpu_reset_clobbers_display)
> +	if (!reset_clobbers_display(gt->i915))
>  		__intel_gt_reset(gt, ALL_ENGINES);
>  
>  	for_each_engine(engine, gt->i915, id)
> -- 
> 2.23.0

-- 
Ville Syrjälä
Intel
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