[Intel-gfx] [PATCH] drm/i915/gen9: Re-allocate DDB only for changed pipes

[Maarten Lankhorst]

Op 28-06-16 om 01:42 schreef Matt Roper:
> When a display update triggers a DDB re-allocation, we should start by
> assuming that only the updated pipes need to be re-allocated (we have
> logic later that may add additional pipes if, e.g., a modeset triggers a
> change to the global allocation).
>
> We were erroneously using the _active_ pipes as our starting point
> rather than the changed pipes.  This causes us to grab CRTC locks that
> we didn't actually need, reducing parallelism.  Given the recent
> non-blocking atomic changes, it also causes legacy pageflips against one
> CRTC to return -EBUSY if there's an outstanding pageflip against a
> different CRTC (a situation easily triggered via compositors like
> Weston).
>
> Fixes: 98d39494d3 ("drm/i915/gen9: Compute DDB allocation at atomic check time (v4)")
> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Signed-off-by: Matt Roper <matthew.d.roper at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index c94521cc..d7f8ba8 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -3879,6 +3879,19 @@ static int skl_update_pipe_wm(struct drm_crtc_state *cstate,
>  	return 0;
>  }
>  
> +static uint32_t
> +pipes_modified(struct drm_atomic_state *state)
> +{
> +	struct drm_crtc *crtc;
> +	struct drm_crtc_state *cstate;
> +	uint32_t i, ret = 0;
> +
> +	for_each_crtc_in_state(state, crtc, cstate, i)
> +		ret |= drm_crtc_mask(crtc);
> +
> +	return ret;
> +}
> +
>  static int
>  skl_compute_ddb(struct drm_atomic_state *state)
>  {
> @@ -3887,7 +3900,7 @@ skl_compute_ddb(struct drm_atomic_state *state)
>  	struct intel_atomic_state *intel_state = to_intel_atomic_state(state);
>  	struct intel_crtc *intel_crtc;
>  	struct skl_ddb_allocation *ddb = &intel_state->wm_results.ddb;
> -	unsigned realloc_pipes = dev_priv->active_crtcs;
> +	uint32_t realloc_pipes = pipes_modified(state);
>  	int ret;
>  
>  	/*

Hey,

Thanks, this is the original bug that triggered the need for "[PATCH] drm/atomic: Make drm_atomic_legacy_backoff reset crtc->acquire_ctx".
Fixing this should remove unnecessary stalls in atomic commit. :-)

Reviewed-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>