[RFC v2 14/20] drm/nouveau/kms/nv50-: Use downstream DP clock limits for mode validation

[Lyude Paul <lyude@redhat.com>]

This adds support for querying the maximum clock rate of a downstream
port on a DisplayPort connection. Generally, downstream ports refer to
active dongles which can have their own pixel clock limits.

Note as well, we also start marking the connector as disconnected if we
can't read the DPCD, since we wouldn't be able to do anything without
DPCD access anyway.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Ben Skeggs <bskeggs@redhat.com>
---
 drivers/gpu/drm/nouveau/dispnv50/disp.c   |  3 +++
 drivers/gpu/drm/nouveau/nouveau_dp.c      | 15 +++++++++++----
 drivers/gpu/drm/nouveau/nouveau_encoder.h |  1 +
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index 0d6879c532bec..c33b026c1f43f 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -1257,7 +1257,10 @@ nv50_mstc_detect(struct drm_connector *connector,
 
 	ret = drm_dp_mst_detect_port(connector, ctx, mstc->port->mgr,
 				     mstc->port);
+	if (ret != connector_status_connected)
+		goto out;
 
+out:
 	pm_runtime_mark_last_busy(connector->dev->dev);
 	pm_runtime_put_autosuspend(connector->dev->dev);
 	return ret;
diff --git a/drivers/gpu/drm/nouveau/nouveau_dp.c b/drivers/gpu/drm/nouveau/nouveau_dp.c
index 71d095409c90d..c200f197083f9 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dp.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dp.c
@@ -61,6 +61,11 @@ nouveau_dp_probe_dpcd(struct nouveau_connector *nv_connector,
 			mstm->can_mst = drm_dp_has_mst(aux, dpcd);
 	}
 
+	ret = drm_dp_downstream_read_info(aux, dpcd,
+					  outp->dp.downstream_ports);
+	if (ret < 0)
+		return connector_status_disconnected;
+
 	return connector_status_connected;
 }
 
@@ -176,8 +181,6 @@ void nouveau_dp_irq(struct nouveau_drm *drm,
 /* TODO:
  * - Use the minimum possible BPC here, once we add support for the max bpc
  *   property.
- * - Validate the mode against downstream port caps (see
- *   drm_dp_downstream_max_clock())
  * - Validate against the DP caps advertised by the GPU (we don't check these
  *   yet)
  */
@@ -188,15 +191,19 @@ nv50_dp_mode_valid(struct drm_connector *connector,
 		   unsigned *out_clock)
 {
 	const unsigned min_clock = 25000;
-	unsigned max_clock, clock;
+	unsigned max_clock, ds_clock, clock;
 	enum drm_mode_status ret;
 
 	if (mode->flags & DRM_MODE_FLAG_INTERLACE && !outp->caps.dp_interlace)
 		return MODE_NO_INTERLACE;
 
 	max_clock = outp->dp.link_nr * outp->dp.link_bw;
-	clock = mode->clock * (connector->display_info.bpc * 3) / 10;
+	ds_clock = drm_dp_downstream_max_clock(outp->dp.dpcd,
+					       outp->dp.downstream_ports);
+	if (ds_clock)
+		max_clock = min(max_clock, ds_clock);
 
+	clock = mode->clock * (connector->display_info.bpc * 3) / 10;
 	ret = nouveau_conn_mode_clock_valid(mode, min_clock, max_clock,
 					    &clock);
 	if (out_clock)
diff --git a/drivers/gpu/drm/nouveau/nouveau_encoder.h b/drivers/gpu/drm/nouveau/nouveau_encoder.h
index eef4643f5f982..c1924a4529a7b 100644
--- a/drivers/gpu/drm/nouveau/nouveau_encoder.h
+++ b/drivers/gpu/drm/nouveau/nouveau_encoder.h
@@ -72,6 +72,7 @@ struct nouveau_encoder {
 			struct mutex hpd_irq_lock;
 
 			u8 dpcd[DP_RECEIVER_CAP_SIZE];
+			u8 downstream_ports[DP_MAX_DOWNSTREAM_PORTS];
 			struct drm_dp_desc desc;
 		} dp;
 	};
-- 
2.26.2