linux-kernel - Re: [PATCH v3 6/6] drm/ingenic: Attach bridge chain to encoders

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Date:   Thu, 23 Sep 2021 13:56:36 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Paul Cercueil <paul@...pouillou.net>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        linux-mips <linux-mips@...r.kernel.org>, list@...ndingux.net,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Paul Boddie <paul@...die.org.uk>
Subject: Re: [PATCH v3 6/6] drm/ingenic: Attach bridge chain to encoders



Hi Laurent,

> IMHO it is leaving (mature) dw-hdmi untouched and make attachment of a connector
> in ingenic_drm_bind() depend on some condition.

Since I don't know details of the DRM bridge/encoder/connector APIs), 
let me reformulate the quersion for a condition specifically.

How can one find out in this code fragment from Paul's patch
if drm_brige_attach() did create a connector or not?

I.e. did call drm_connector_attach_encoder(connector, hdmi->bridge.encoder);
on its own?

@@ -1154,20 +1186,36 @@ static int ingenic_drm_bind(struct device *dev, bool has_components)
			bridge = devm_drm_panel_bridge_add_typed(dev, panel,
								 DRM_MODE_CONNECTOR_DPI);

		drm_encoder_helper_add(encoder, &ingenic_drm_encoder_helper_funcs);

-		ret = drm_bridge_attach(encoder, bridge, NULL, 0);
-		if (ret)
+		ib->bridge.funcs = &ingenic_drm_bridge_funcs;
+		ib->next_bridge = bridge;
+
+		ret = drm_bridge_attach(encoder, &ib->bridge, NULL,
+					DRM_BRIDGE_ATTACH_NO_CONNECTOR);
+		if (ret) {
+			dev_err(dev, "Unable to attach bridge\n");
			return ret;
+		}
+
+		connector = drm_bridge_connector_init(drm, encoder);
+		if (IS_ERR(connector)) {
+			dev_err(dev, "Unable to init connector\n");
+			return PTR_ERR(connector);
+		}
+
+		drm_connector_attach_encoder(connector, encoder);
	}

A problem may be that "connector" is unknown before drm_bridge_connector_init()
is called.

Then I think I can propose a fallback solution to drm_bridge_attach(, 0) if
drm_bridge_attach(, DRM_BRIDGE_ATTACH_NO_CONNECTOR) fails. 

BR and thanks,
Nikolaus