drm/amd/display: Determine early if a link has supported encoders (v2)

Avoid initializing DDC, HPD, etc. when we know that the link is
not going to be constructed because it has no supported encoders.

This is mainly useful for old GPUs which may have encoders such
as TRAVIS and NUTMEG that are not yet supported by DC.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: Timur Kristóf

drivers/gpu/drm/amd/display/dc/link/link_factory.c

@@ -451,6 +451,14 @@ static enum channel_id get_ddc_line(struct dc_link *link)
 	return channel;
 }
 
+static bool transmitter_supported(const enum transmitter transmitter)
+{
+	return transmitter != TRANSMITTER_UNKNOWN &&
+		transmitter != TRANSMITTER_NUTMEG_CRT &&
+		transmitter != TRANSMITTER_TRAVIS_CRT &&
+		transmitter != TRANSMITTER_TRAVIS_LCD;
+}
+
 static bool construct_phy(struct dc_link *link,
 			      const struct link_init_data *init_params)
 {
@@ -482,6 +490,17 @@ static bool construct_phy(struct dc_link *link,
 	link->link_id =
 		bios->funcs->get_connector_id(bios, init_params->connector_index);
 
+	/* Determine early if the link has any supported encoders,
+	 * so that we avoid initializing DDC and HPD, etc.
+	 */
+	bp_funcs->get_src_obj(bios, link->link_id, 0, &enc_init_data.encoder);
+	enc_init_data.transmitter = translate_encoder_to_transmitter(enc_init_data.encoder);
+
+	if (!transmitter_supported(enc_init_data.transmitter)) {
+		DC_LOG_WARNING("link_id %d has unsupported encoder\n", link->link_id.id);
+		return false;
+	}
+
 	link->ep_type = DISPLAY_ENDPOINT_PHY;
 
 	DC_LOG_DC("BIOS object table - link_id: %d", link->link_id.id);
@@ -611,16 +630,12 @@ static bool construct_phy(struct dc_link *link,
 		dal_ddc_get_line(get_ddc_pin(link->ddc));
 
 	enc_init_data.ctx = dc_ctx;
-	bp_funcs->get_src_obj(dc_ctx->dc_bios, link->link_id, 0,
-			      &enc_init_data.encoder);
 	enc_init_data.connector = link->link_id;
 	enc_init_data.channel = get_ddc_line(link);
 	enc_init_data.hpd_source = get_hpd_line(link);
 
 	link->hpd_src = enc_init_data.hpd_source;
 
-	enc_init_data.transmitter =
-		translate_encoder_to_transmitter(enc_init_data.encoder);
 	link->link_enc =
 		link->dc->res_pool->funcs->link_enc_create(dc_ctx, &enc_init_data);