Re: [PATCH] drm/i915: Unset legacy_cursor_update early in intel_atomic_commit

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

On Wed, Sep 13, 2017 at 11:25:54AM +0200, Maarten Lankhorst wrote:
> Commit b44d5c0c105a ("drm/i915: Always wait for flip_done, v2.") removed
> the call to wait_for_vblanks and replaced it with flip_done.
> 
> Unfortunately legacy_cursor_update was unset too late, and the
> replacement call drm_atomic_helper_wait_for_flip_done() was
> a noop. Make sure that its unset before setup_commit() is
> called to fix this issue.
> 
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Fixes: b44d5c0c105a ("drm/i915: Always wait for flip_done, v2.")
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102675
> Testcase: kms_cursor_crc
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Reported-by: Marta Löfstedt <marta.lofstedt@intel.com>
> Cc: Marta Löfstedt <marta.lofstedt@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 44 ++++++++++++++++++++----------------
>  1 file changed, 24 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index ba76b2db939c..c1da48d77c8e 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -12412,23 +12412,14 @@ static int intel_atomic_commit(struct drm_device *dev,
>  {
>  	struct intel_atomic_state *intel_state = to_intel_atomic_state(state);
>  	struct drm_i915_private *dev_priv = to_i915(dev);
> -	int ret = 0;
> -
> -	ret = drm_atomic_helper_setup_commit(state, nonblock);
> -	if (ret)
> -		return ret;
> +	struct drm_crtc_state *new_crtc_state;
> +	struct drm_crtc *crtc;

I'd prefer to see intel_ types.

> +	int i, ret = 0;
>  
>  	drm_atomic_state_get(state);
>  	i915_sw_fence_init(&intel_state->commit_ready,
>  			   intel_atomic_commit_ready);
>  
> -	ret = intel_atomic_prepare_commit(dev, state);
> -	if (ret) {
> -		DRM_DEBUG_ATOMIC("Preparing state failed with %i\n", ret);
> -		i915_sw_fence_commit(&intel_state->commit_ready);
> -		return ret;
> -	}
> -
>  	/*
>  	 * The intel_legacy_cursor_update() fast path takes care
>  	 * of avoiding the vblank waits for simple cursor
> @@ -12437,19 +12428,32 @@ static int intel_atomic_commit(struct drm_device *dev,
>  	 * updates happen during the correct frames. Gen9+ have
>  	 * double buffered watermarks and so shouldn't need this.
>  	 *
> -	 * Do this after drm_atomic_helper_setup_commit() and
> -	 * intel_atomic_prepare_commit() because we still want
> -	 * to skip the flip and fb cleanup waits. Although that
> -	 * does risk yanking the mapping from under the display
> -	 * engine.
> +	 * Unset state->legacy_cursor_update before the call to
> +	 * drm_atomic_helper_setup_commit() because otherwise
> +	 * drm_atomic_helper_wait_for_flip_done() is a noop and
> +	 * we get FIFO underruns because we didn't wait
> +	 * for vblank.
>  	 *
>  	 * FIXME doing watermarks and fb cleanup from a vblank worker
>  	 * (assuming we had any) would solve these problems.
>  	 */
> -	if (INTEL_GEN(dev_priv) < 9)
> -		state->legacy_cursor_update = false;
> +	if (INTEL_GEN(dev_priv) < 9 && state->legacy_cursor_update) {
> +		for_each_new_crtc_in_state(state, crtc, new_crtc_state, i)
> +			if (to_intel_crtc_state(new_crtc_state)->wm.need_postvbl_update)
> +				state->legacy_cursor_update = false;
> +	}

Hmm. I don't think we can rely on need_postvbl_update at this point.
Pre-g4x code won't set it. We already made the decision to not use the
fast path, so explicitly setting legacy_cursor_update=false should still
be fine, no?

> +
> +	ret = intel_atomic_prepare_commit(dev, state);
> +	if (ret) {
> +		DRM_DEBUG_ATOMIC("Preparing state failed with %i\n", ret);
> +		i915_sw_fence_commit(&intel_state->commit_ready);
> +		return ret;
> +	}
> +
> +	ret = drm_atomic_helper_setup_commit(state, nonblock);
> +	if (!ret)
> +		ret = drm_atomic_helper_swap_state(state, true);
>  
> -	ret = drm_atomic_helper_swap_state(state, true);
>  	if (ret) {
>  		i915_sw_fence_commit(&intel_state->commit_ready);
>  
> -- 
> 2.14.1
> 
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-- 
Ville Syrjälä
Intel OTC
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