drm/i915/dsi: fix VBT send packet port selection for ICL+

The VBT send packet port selection was never updated for ICL+ where the
2nd link is on port B instead of port C as in VLV+ DSI.

First, single link DSI needs to use the configured port instead of
relying on the VBT sequence block port. Remove the hard-coded port C
check here and make it generic. For reference, see commit f915084e
("drm/i915: Changes related to the sequence port no for") for the
original VLV specific fix.

Second, the sequence block port number is either 0 or 1, where 1
indicates the 2nd link. Remove the hard-coded port C here for 2nd
link. (This could be a "find second set bit" on DSI ports, but just
check the two possible options.)

Third, sanity check the result with a warning to avoid a NULL pointer
dereference.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5984
Cc: stable@vger.kernel.org # v4.19+
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220520094600.2066945-1-jani.nikula@intel.com

drivers/gpu/drm/i915/display/intel_dsi_vbt.c

@@ -125,9 +125,25 @@ struct i2c_adapter_lookup {
 #define  ICL_GPIO_DDPA_CTRLCLK_2	8
 #define  ICL_GPIO_DDPA_CTRLDATA_2	9
 
-static enum port intel_dsi_seq_port_to_port(u8 port)
+static enum port intel_dsi_seq_port_to_port(struct intel_dsi *intel_dsi,
+					    u8 seq_port)
 {
-	return port ? PORT_C : PORT_A;
+	/*
+	 * If single link DSI is being used on any port, the VBT sequence block
+	 * send packet apparently always has 0 for the port. Just use the port
+	 * we have configured, and ignore the sequence block port.
+	 */
+	if (hweight8(intel_dsi->ports) == 1)
+		return ffs(intel_dsi->ports) - 1;
+
+	if (seq_port) {
+		if (intel_dsi->ports & PORT_B)
+			return PORT_B;
+		else if (intel_dsi->ports & PORT_C)
+			return PORT_C;
+	}
+
+	return PORT_A;
 }
 
 static const u8 *mipi_exec_send_packet(struct intel_dsi *intel_dsi,
@@ -149,15 +165,10 @@ static const u8 *mipi_exec_send_packet(struct intel_dsi *intel_dsi,
 
 	seq_port = (flags >> MIPI_PORT_SHIFT) & 3;
 
-	/* For DSI single link on Port A & C, the seq_port value which is
-	 * parsed from Sequence Block#53 of VBT has been set to 0
-	 * Now, read/write of packets for the DSI single link on Port A and
-	 * Port C will based on the DVO port from VBT block 2.
-	 */
-	if (intel_dsi->ports == (1 << PORT_C))
-		port = PORT_C;
-	else
-		port = intel_dsi_seq_port_to_port(seq_port);
+	port = intel_dsi_seq_port_to_port(intel_dsi, seq_port);
+
+	if (drm_WARN_ON(&dev_priv->drm, !intel_dsi->dsi_hosts[port]))
+		goto out;
 
 	dsi_device = intel_dsi->dsi_hosts[port]->device;
 	if (!dsi_device) {