drm/omap: Fix and improve crtc and overlay manager correlation

The omapdrm driver currently takes a config/module arg to figure out the number
of crtcs it needs to create. We could create as many crtcs as there are overlay
managers in the DSS hardware, but we don't do that because each crtc eats up
one DSS overlay, and that reduces the number of planes we can attach to a single
crtc.

Since the number of crtcs may be lesser than the number of hardware overlay
managers, we need to figure out which overlay managers to use for our crtcs. The
current approach is to use pipe2chan(), which returns a higher numbered manager
for the crtc.

The problem with this approach is that it assumes that the overlay managers we
choose will connect to the encoders the platform's panels are going to use,
this isn't true, an overlay manager connects only to a few outputs/encoders, and
choosing any overlay manager for our crtc might lead to a situation where the
encoder cannot connect to any of the crtcs we have chosen. For example, an
omap5-panda board has just one hdmi output. If num_crtc is set to 1, with the
current approach, pipe2chan will pick up the LCD2 overlay manager, which cannot
connect to the hdmi encoder at all. The only manager that could have connected
to hdmi was the TV overlay manager.

Therefore, there is a need to choose our overlay managers keeping in mind the
panels we have on that platform. The new approach iterates through all the
available panels, creates encoders and connectors for them, and then tries to
get a suitable overlay manager to create a crtc which can connect to the
encoders.

We use the dispc_channel field in omap_dss_output to retrieve the desired
overlay manager's channel number, we then check whether the manager had already
been assigned to a crtc or not. If it was already assigned to a crtc, we assume
that out of all the encoders which intend use this crtc, only one will run at a
time. If the overlay manager wan't assigned to a crtc till then, we create a
new crtc and link it with the overlay manager.

This approach just looks for the best dispc_channel for each encoder. On DSS HW,
some encoders can connect to multiple overlay managers. Since we don't try
looking for alternate overlay managers, there is a greater possibility that 2
or more encoders end up asking for the same crtc, causing only one encoder to
run at a time.

Also, this approach isn't the most optimal one, it can do either good or bad
depending on the sequence in which the panels/outputs are parsed. The optimal
way would be some sort of back tracking approach, where we improve the set of
managers we use as we iterate through the list of panels/encoders. That's
something left for later.

Signed-off-by: Archit Taneja <archit@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

1 files changed, 129 insertions, 28 deletions

diff --git a/drivers/gpu/drm/omapdrm/omap_drv.c b/drivers/gpu/drm/omapdrm/omap_drv.c
index 77b72259f15..cbaa00338b6 100644
--- a/drivers/gpu/drm/omapdrm/omap_drv.c
+++ b/drivers/gpu/drm/omapdrm/omap_drv.c
@@ -74,49 +74,48 @@ static int get_connector_type(struct omap_dss_device *dssdev)
 	}
 }
 
+static bool channel_used(struct drm_device *dev, enum omap_channel channel)
+{
+	struct omap_drm_private *priv = dev->dev_private;
+	int i;
+
+	for (i = 0; i < priv->num_crtcs; i++) {
+		struct drm_crtc *crtc = priv->crtcs[i];
+
+		if (omap_crtc_channel(crtc) == channel)
+			return true;
+	}
+
+	return false;
+}
+
 static int omap_modeset_init(struct drm_device *dev)
 {
 	struct omap_drm_private *priv = dev->dev_private;
 	struct omap_dss_device *dssdev = NULL;
 	int num_ovls = dss_feat_get_num_ovls();
-	int id;
+	int num_mgrs = dss_feat_get_num_mgrs();
+	int num_crtcs;
+	int i, id = 0;
 
 	drm_mode_config_init(dev);
 
 	omap_drm_irq_install(dev);
 
 	/*
-	 * Create private planes and CRTCs for the last NUM_CRTCs overlay
-	 * plus manager:
-	 */
-	for (id = 0; id < min(num_crtc, num_ovls); id++) {
-		struct drm_plane *plane;
-		struct drm_crtc *crtc;
-
-		plane = omap_plane_init(dev, id, true);
-		crtc = omap_crtc_init(dev, plane, pipe2chan(id), id);
-
-		BUG_ON(priv->num_crtcs >= ARRAY_SIZE(priv->crtcs));
-		priv->crtcs[id] = crtc;
-		priv->num_crtcs++;
-
-		priv->planes[id] = plane;
-		priv->num_planes++;
-	}
-
-	/*
-	 * Create normal planes for the remaining overlays:
+	 * We usually don't want to create a CRTC for each manager, at least
+	 * not until we have a way to expose private planes to userspace.
+	 * Otherwise there would not be enough video pipes left for drm planes.
+	 * We use the num_crtc argument to limit the number of crtcs we create.
 	 */
-	for (; id < num_ovls; id++) {
-		struct drm_plane *plane = omap_plane_init(dev, id, false);
+	num_crtcs = min3(num_crtc, num_mgrs, num_ovls);
 
-		BUG_ON(priv->num_planes >= ARRAY_SIZE(priv->planes));
-		priv->planes[priv->num_planes++] = plane;
-	}
+	dssdev = NULL;
 
 	for_each_dss_dev(dssdev) {
 		struct drm_connector *connector;
 		struct drm_encoder *encoder;
+		enum omap_channel channel;
 
 		if (!dssdev->driver) {
 			dev_warn(dev->dev, "%s has no driver.. skipping it\n",
@@ -157,16 +156,118 @@ static int omap_modeset_init(struct drm_device *dev)
 
 		drm_mode_connector_attach_encoder(connector, encoder);
 
+		/*
+		 * if we have reached the limit of the crtcs we are allowed to
+		 * create, let's not try to look for a crtc for this
+		 * panel/encoder and onwards, we will, of course, populate the
+		 * the possible_crtcs field for all the encoders with the final
+		 * set of crtcs we create
+		 */
+		if (id == num_crtcs)
+			continue;
+
+		/*
+		 * get the recommended DISPC channel for this encoder. For now,
+		 * we only try to get create a crtc out of the recommended, the
+		 * other possible channels to which the encoder can connect are
+		 * not considered.
+		 */
+		channel = dssdev->output->dispc_channel;
+
+		/*
+		 * if this channel hasn't already been taken by a previously
+		 * allocated crtc, we create a new crtc for it
+		 */
+		if (!channel_used(dev, channel)) {
+			struct drm_plane *plane;
+			struct drm_crtc *crtc;
+
+			plane = omap_plane_init(dev, id, true);
+			crtc = omap_crtc_init(dev, plane, channel, id);
+
+			BUG_ON(priv->num_crtcs >= ARRAY_SIZE(priv->crtcs));
+			priv->crtcs[id] = crtc;
+			priv->num_crtcs++;
+
+			priv->planes[id] = plane;
+			priv->num_planes++;
+
+			id++;
+		}
+	}
+
+	/*
+	 * we have allocated crtcs according to the need of the panels/encoders,
+	 * adding more crtcs here if needed
+	 */
+	for (; id < num_crtcs; id++) {
+
+		/* find a free manager for this crtc */
+		for (i = 0; i < num_mgrs; i++) {
+			if (!channel_used(dev, i)) {
+				struct drm_plane *plane;
+				struct drm_crtc *crtc;
+
+				plane = omap_plane_init(dev, id, true);
+				crtc = omap_crtc_init(dev, plane, i, id);
+
+				BUG_ON(priv->num_crtcs >=
+					ARRAY_SIZE(priv->crtcs));
+
+				priv->crtcs[id] = crtc;
+				priv->num_crtcs++;
+
+				priv->planes[id] = plane;
+				priv->num_planes++;
+
+				break;
+			} else {
+				continue;
+			}
+		}
+
+		if (i == num_mgrs) {
+			/* this shouldn't really happen */
+			dev_err(dev->dev, "no managers left for crtc\n");
+			return -ENOMEM;
+		}
+	}
+
+	/*
+	 * Create normal planes for the remaining overlays:
+	 */
+	for (; id < num_ovls; id++) {
+		struct drm_plane *plane = omap_plane_init(dev, id, false);
+
+		BUG_ON(priv->num_planes >= ARRAY_SIZE(priv->planes));
+		priv->planes[priv->num_planes++] = plane;
+	}
+
+	for (i = 0; i < priv->num_encoders; i++) {
+		struct drm_encoder *encoder = priv->encoders[i];
+		struct omap_dss_device *dssdev =
+					omap_encoder_get_dssdev(encoder);
+
 		/* figure out which crtc's we can connect the encoder to: */
 		encoder->possible_crtcs = 0;
 		for (id = 0; id < priv->num_crtcs; id++) {
-			enum omap_dss_output_id supported_outputs =
-					dss_feat_get_supported_outputs(pipe2chan(id));
+			struct drm_crtc *crtc = priv->crtcs[id];
+			enum omap_channel crtc_channel;
+			enum omap_dss_output_id supported_outputs;
+
+			crtc_channel = omap_crtc_channel(crtc);
+			supported_outputs =
+				dss_feat_get_supported_outputs(crtc_channel);
+
 			if (supported_outputs & dssdev->output->id)
 				encoder->possible_crtcs |= (1 << id);
 		}
 	}
 
+	DBG("registered %d planes, %d crtcs, %d encoders and %d connectors\n",
+		priv->num_planes, priv->num_crtcs, priv->num_encoders,
+		priv->num_connectors);
+
 	dev->mode_config.min_width = 32;
 	dev->mode_config.min_height = 32;