On Tue, Oct 16, 2018 at 03:01:25PM -0700, Paulo Zanoni wrote:
> Before the patch, if a plane was not visible,
> skl_compute_plane_wm_params() would return early without writing
> anything to the wm_params struct. This would leave garbage in the
> struct since it is not previously zeroed, and then we would later
> check for wm_params.is_planar, which could be true due to the usage of
> uninitialized memory. This would lead us to calculate the zeroed
> watermarks for the second inexistent plane and mark the plane as a
> planar plane. Then later this check would affect our decisions in
> skl_write_plane_wm().
>
> I can't see how this would lead to a noticeable bug in our code, but
> it leads us to calculate watermarks for every level + transition
> watermarks, twice (due to the is_planar bug). So the fix saves us a
> lot of instructions.
>
> This problem was found when I decided to add a DRM_ERROR for the
> currently unsupported planar formats on ICL: kms_cursor_legacy would
> trigger the error message without using planar formats.
>
> So the fix we adopt in this patch is to create a new watermark
> parameter called plane_visible and use it to avoid computing the
> watermarks for invisible planes later. We also remove the checks that
> are now made redundant by it.
>
> Testcase: igt/kms_cursor_legacy/nonblocking-modeset-vs-cursor-atomic
> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_drv.h | 1 +
> drivers/gpu/drm/i915/intel_pm.c | 15 ++++++---------
> 2 files changed, 7 insertions(+), 9 deletions(-)
>
> The error message mentioned above isd the one added by patch 06 of the
> series.
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 3616b718b5d2..4b1e8471609b 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1250,6 +1250,7 @@ struct skl_wm_level {
>
> /* Stores plane specific WM parameters */
> struct skl_wm_params {
> + bool plane_visible;
> bool x_tiled, y_tiled;
> bool rc_surface;
> bool is_planar;
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 18157c6ee126..9043ffe40ce8 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -4532,7 +4532,8 @@ skl_compute_plane_wm_params(const struct drm_i915_private *dev_priv,
> to_intel_atomic_state(cstate->base.state);
> bool apply_memory_bw_wa = skl_needs_memory_bw_wa(state);
>
> - if (!intel_wm_plane_visible(cstate, intel_pstate))
> + wp->plane_visible = intel_wm_plane_visible(cstate, intel_pstate);
> + if (!wp->plane_visible)
> return 0;
>
> /* only NV12 format has two planes */
> @@ -4645,8 +4646,7 @@ static int skl_compute_plane_wm(const struct drm_i915_private *dev_priv,
> bool apply_memory_bw_wa = skl_needs_memory_bw_wa(state);
> uint32_t min_disp_buf_needed;
>
> - if (latency == 0 ||
> - !intel_wm_plane_visible(cstate, intel_pstate)) {
> + if (latency == 0) {
> result->plane_en = false;
> return 0;
> }
> @@ -4805,9 +4805,6 @@ skl_compute_wm_levels(const struct drm_i915_private *dev_priv,
> enum plane_id intel_plane_id = intel_plane->id;
> int ret;
>
> - if (WARN_ON(!intel_pstate->base.fb))
> - return -EINVAL;
> -
> ddb_blocks = plane_id ?
> skl_ddb_entry_size(&ddb->uv_plane[pipe][intel_plane_id]) :
> skl_ddb_entry_size(&ddb->plane[pipe][intel_plane_id]);
> @@ -4876,9 +4873,6 @@ static void skl_compute_transition_wm(struct intel_crtc_state *cstate,
> const uint16_t trans_amount = 10; /* This is configurable amount */
> uint16_t wm0_sel_res_b, trans_offset_b, res_blocks;
>
> - if (!cstate->base.active)
> - goto exit;
> -
> /* Transition WM are not recommended by HW team for GEN9 */
> if (INTEL_GEN(dev_priv) <= 9)
> goto exit;
> @@ -4965,6 +4959,9 @@ static int skl_build_pipe_wm(struct intel_crtc_state *cstate,
> if (ret)
> return ret;
>
> + if (!wm_params.plane_visible)
> + continue;
> +
So this will now skip both skl_compute_wm_levels() and
skl_compute_transition_wm() for this plane, and we've
zeroed the entire pipe_wm->planes thing earlier.
Seems good.
Since we're only checking this in this one place I don't
think we really need to add wm_params.plane_visible. Could
just do the intel_wm_plane_visible() check right here no?
Either way:
Reviewed-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> ret = skl_compute_wm_levels(dev_priv, ddb, cstate,
> intel_pstate, &wm_params, wm, 0);
> if (ret)
> --
> 2.14.4
>
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> Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
--
Ville Syrjälä
Intel
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