Re: [PATCH v4 3/6] drm/i915/skl: Only flush pipes when we change the ddb allocation

Matt Roper
2016-07-28T13:14:30Z

On Tue, Jul 26, 2016 at 01:34:39PM -0400, Lyude wrote:
> Manual pipe flushes are only necessary in order to make sure that we prevent
> pipes with changed ddb allocations from overlapping from one another at
> any point in time. Additionally, forcing us to wait for the next vblank
> every time we have to update the watermark values because the cursor was
> moving between screens will introduce a rather noticable lag for users.
>
> Signed-off-by: Lyude <cpaul@redhat.com>
> Cc: stable@vger.kernel.org
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
> Cc: Hans de Goede <hdegoede@redhat.com>
> Cc: Matt Roper <matthew.d.roper@intel.com>
> ---
> drivers/gpu/drm/i915/i915_drv.h | 1 +
> drivers/gpu/drm/i915/intel_pm.c | 31 +++++++++++++++++++++++++++++--
> 2 files changed, 30 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 1f6fe8c..d65e897 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1597,6 +1597,7 @@ struct skl_ddb_allocation {
>
> struct skl_wm_values {
> unsigned dirty_pipes;
> + bool ddb_changed;
> struct skl_ddb_allocation ddb;
> uint32_t wm_linetime[I915_MAX_PIPES];
> uint32_t plane[I915_MAX_PIPES][I915_MAX_PLANES][8];
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 8ae3f2b..cda4196 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -3892,6 +3892,12 @@ static void skl_flush_wm_values(struct drm_i915_private *dev_priv,
> new_ddb = &new_values->ddb;
> cur_ddb = &dev_priv->wm.skl_hw.ddb;
>
> + /* We only ever need to flush when the ddb allocations change */
> + if (!new_values->ddb_changed)
> + return;
> +
> + new_values->ddb_changed = false;
> +
> /*
> * First pass: flush the pipes with the new allocation contained into
> * the old space.
> @@ -3996,6 +4002,22 @@ pipes_modified(struct drm_atomic_state *state)
> return ret;
> }
>
> +static bool
> +skl_pipe_ddb_changed(struct skl_ddb_allocation *old,
> + struct skl_ddb_allocation *new,
> + enum pipe pipe)
> +{
> + if (memcmp(&old->pipe[pipe], &new->pipe[pipe],
> + sizeof(old->pipe[pipe])) != 0 ||
> + memcmp(&old->plane[pipe], &new->plane[pipe],
> + sizeof(old->plane[pipe])) != 0 ||
> + memcmp(&old->y_plane[pipe], &new->y_plane[pipe],
> + sizeof(old->y_plane[pipe])) != 0)
> + return true;
> +
> + return false;
> +}
> +
> static int
> skl_compute_ddb(struct drm_atomic_state *state)
> {
> @@ -4003,7 +4025,8 @@ skl_compute_ddb(struct drm_atomic_state *state)
> struct drm_i915_private *dev_priv = to_i915(dev);
> 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;
> + struct skl_ddb_allocation *new_ddb = &intel_state->wm_results.ddb;
> + struct skl_ddb_allocation *old_ddb = &dev_priv->wm.skl_hw.ddb;
> uint32_t realloc_pipes = pipes_modified(state);
> int ret;
>
> @@ -4041,9 +4064,13 @@ skl_compute_ddb(struct drm_atomic_state *state)
> if (IS_ERR(cstate))
> return PTR_ERR(cstate);
>
> - ret = skl_allocate_pipe_ddb(cstate, ddb);
> + ret = skl_allocate_pipe_ddb(cstate, new_ddb);
> if (ret)
> return ret;
> +
> + if (!intel_state->wm_results.ddb_changed &&

I think you can simplify and drop the first part of this condition here,
but in general,

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>

> + skl_pipe_ddb_changed(old_ddb, new_ddb, intel_crtc->pipe))
> + intel_state->wm_results.ddb_changed = true;
> }
>
> return 0;
> --
> 2.7.4
>

--
Matt Roper
Graphics Software Engineer
IoTG Platform Enabling & Development
Intel Corporation
(916) 356-2795