On Mon, 29 Aug 2016, Lyude <cpaul@xxxxxxxxxx> wrote:
> i915 sometimes needs to disable planes in the middle of an atomic
> commit, and then reenable them later in the same commit. Because of
> this, we can't make the assumption that the state of the plane actually
> changed. Since the state of the plane hasn't actually changed, neither
> have it's watermarks. And if the watermarks hasn't changed then we
> haven't populated skl_results with anything, which means we'll end up
> zeroing out a plane's watermarks in the middle of the atomic commit
> without restoring them later.
I would appreciate a (brief) description of what the failure mode is in
this case.
BR,
Jani.
>
> Changes since v1:
> - Fix incorrect use of "it's"
>
> Signed-off-by: Lyude <cpaul@xxxxxxxxxx>
> Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Fixes: 62e0fb880123 ("drm/i915/skl: Update plane watermarks atomically
> during plane updates")
>
> Signed-off-by: Lyude <cpaul@xxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/intel_display.c | 7 ++++++-
> drivers/gpu/drm/i915/intel_sprite.c | 9 +++++++--
> 2 files changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index e4e6141..13e47a7 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -3448,7 +3448,12 @@ static void skylake_disable_primary_plane(struct drm_plane *primary,
> struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
> int pipe = intel_crtc->pipe;
>
> - skl_write_plane_wm(intel_crtc, &dev_priv->wm.skl_results, 0);
> + /*
> + * We only populate skl_results on watermark updates, and if the
> + * plane's visiblity isn't actually changing neither is its watermarks.
> + */
> + if (!crtc->primary->state->visible)
> + skl_write_plane_wm(intel_crtc, &dev_priv->wm.skl_results, 0);
>
> I915_WRITE(PLANE_CTL(pipe, 0), 0);
> I915_WRITE(PLANE_SURF(pipe, 0), 0);
> diff --git a/drivers/gpu/drm/i915/intel_sprite.c b/drivers/gpu/drm/i915/intel_sprite.c
> index 0df783a..73a521f 100644
> --- a/drivers/gpu/drm/i915/intel_sprite.c
> +++ b/drivers/gpu/drm/i915/intel_sprite.c
> @@ -292,8 +292,13 @@ skl_disable_plane(struct drm_plane *dplane, struct drm_crtc *crtc)
> const int pipe = intel_plane->pipe;
> const int plane = intel_plane->plane + 1;
>
> - skl_write_plane_wm(to_intel_crtc(crtc), &dev_priv->wm.skl_results,
> - plane);
> + /*
> + * We only populate skl_results on watermark updates, and if the
> + * plane's visiblity isn't actually changing neither is its watermarks.
> + */
> + if (!dplane->state->visible)
> + skl_write_plane_wm(to_intel_crtc(crtc),
> + &dev_priv->wm.skl_results, plane);
>
> I915_WRITE(PLANE_CTL(pipe, plane), 0);
--
Jani Nikula, Intel Open Source Technology Center
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