drm/i915: compute masks of crtcs affected in set_mode

This is definetely a bit more generic than currently required, but if
we keep track of all crtcs that need to be disabled/enable (because
they loose an encoder or something similar), crtcs that get completely
disabled and those that we need to do an actual mode change nicely
prepares us for global modeset operations on multiple crtcs.

The only big thing missing here would be a global resource allocation
step (for e.g. pch plls), which would equally frob these bitmasks if
e.g. a crtc only needs a new pll. Or if we need to enable dithering on
an another pipe due to bandwidth constrains somewhere.

These masks aren't yet put to use in this patch, this will follow in the
next one.

v2-v5: Fix up the computations for good (hopefully).

v6: Fixup a confusion reported by Damien Lespiau: I've conserved the
(imo braindead) behaviour of the crtc helper to disable _any_
disconnected outputs if we do a modeset, even when that newly disabled
connector isn't connected to the crtc being changed by the modeset.

The effect of that is that we could disable an arbitrary number of
unrelated crtcs, which I haven't taken into account when writing this
code. Fix this up.

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -6706,6 +6706,98 @@ fail:
 	return ERR_PTR(-EINVAL);
 }
 
+/* Computes which crtcs are affected and sets the relevant bits in the mask. For
+ * simplicity we use the crtc's pipe number (because it's easier to obtain). */
+static void
+intel_modeset_affected_pipes(struct drm_crtc *crtc, unsigned *modeset_pipes,
+			     unsigned *prepare_pipes, unsigned *disable_pipes)
+{
+	struct intel_crtc *intel_crtc;
+	struct drm_device *dev = crtc->dev;
+	struct intel_encoder *encoder;
+	struct intel_connector *connector;
+	struct drm_crtc *tmp_crtc;
+
+	*disable_pipes = *modeset_pipes = *prepare_pipes = 0;
+
+	/* Check which crtcs have changed outputs connected to them, these need
+	 * to be part of the prepare_pipes mask. We don't (yet) support global
+	 * modeset across multiple crtcs, so modeset_pipes will only have one
+	 * bit set at most. */
+	list_for_each_entry(connector, &dev->mode_config.connector_list,
+			    base.head) {
+		if (connector->base.encoder == &connector->new_encoder->base)
+			continue;
+
+		if (connector->base.encoder) {
+			tmp_crtc = connector->base.encoder->crtc;
+
+			*prepare_pipes |= 1 << to_intel_crtc(tmp_crtc)->pipe;
+		}
+
+		if (connector->new_encoder)
+			*prepare_pipes |=
+				1 << connector->new_encoder->new_crtc->pipe;
+	}
+
+	list_for_each_entry(encoder, &dev->mode_config.encoder_list,
+			    base.head) {
+		if (encoder->base.crtc == &encoder->new_crtc->base)
+			continue;
+
+		if (encoder->base.crtc) {
+			tmp_crtc = encoder->base.crtc;
+
+			*prepare_pipes |= 1 << to_intel_crtc(tmp_crtc)->pipe;
+		}
+
+		if (encoder->new_crtc)
+			*prepare_pipes |= 1 << encoder->new_crtc->pipe;
+	}
+
+	/* Check for any pipes that will be fully disabled ... */
+	list_for_each_entry(intel_crtc, &dev->mode_config.crtc_list,
+			    base.head) {
+		bool used = false;
+
+		/* Don't try to disable disabled crtcs. */
+		if (!intel_crtc->base.enabled)
+			continue;
+
+		list_for_each_entry(encoder, &dev->mode_config.encoder_list,
+				    base.head) {
+			if (encoder->new_crtc == intel_crtc)
+				used = true;
+		}
+
+		if (!used)
+			*disable_pipes |= 1 << intel_crtc->pipe;
+	}
+
+
+	/* set_mode is also used to update properties on life display pipes. */
+	intel_crtc = to_intel_crtc(crtc);
+	if (crtc->enabled)
+		*prepare_pipes |= 1 << intel_crtc->pipe;
+
+	/* We only support modeset on one single crtc, hence we need to do that
+	 * only for the passed in crtc iff we change anything else than just
+	 * disable crtcs.
+	 *
+	 * This is actually not true, to be fully compatible with the old crtc
+	 * helper we automatically disable _any_ output (i.e. doesn't need to be
+	 * connected to the crtc we're modesetting on) if it's disconnected.
+	 * Which is a rather nutty api (since changed the output configuration
+	 * without userspace's explicit request can lead to confusion), but
+	 * alas. Hence we currently need to modeset on all pipes we prepare. */
+	if (*prepare_pipes)
+		*modeset_pipes = *prepare_pipes;
+
+	/* ... and mask these out. */
+	*modeset_pipes &= ~(*disable_pipes);
+	*prepare_pipes &= ~(*disable_pipes);
+}
+
 bool intel_set_mode(struct drm_crtc *crtc,
 		    struct drm_display_mode *mode,
 		    int x, int y, struct drm_framebuffer *fb)
@@ -6715,8 +6807,12 @@ bool intel_set_mode(struct drm_crtc *crtc,
 	struct drm_display_mode *adjusted_mode, saved_mode, saved_hwmode;
 	struct drm_encoder_helper_funcs *encoder_funcs;
 	struct drm_encoder *encoder;
+	unsigned disable_pipe, prepare_pipes, modeset_pipes;
 	bool ret = true;
 
+	intel_modeset_affected_pipes(crtc, &modeset_pipes,
+				     &prepare_pipes, &disable_pipe);
+
 	intel_modeset_commit_output_state(dev);
 
 	crtc->enabled = drm_helper_crtc_in_use(crtc);