drm: apple: answer the DPTX port's group 1 calls as macOS does

drivers/gpu/drm/apple/afk.c

@@ -493,14 +493,12 @@ static void afk_recv_handle_reply(struct apple_dcp_afkep *ep, u32 channel,
 		dma_free_coherent(ep->dcp->dev, txlen, txbuf, txbuf_dma);
 }
 
+/* A call from DCP: one word ahead of the call header AP sends. */
 struct epic_std_service_ap_call {
 	__le32 unk0;
-	__le32 unk1;
-	__le32 type;
-	__le32 len;
-	__le32 magic;
-	u8 _unk[48];
+	struct epic_service_call call;
 } __attribute__((packed));
+static_assert(sizeof(struct epic_std_service_ap_call) == 68);
 
 static void afk_recv_handle_std_service(struct apple_dcp_afkep *ep, u32 channel,
 					u32 type, struct epic_hdr *ehdr,
@@ -525,30 +523,56 @@ static void afk_recv_handle_std_service(struct apple_dcp_afkep *ep, u32 channel,
 	if (type == EPIC_TYPE_NOTIFY && eshdr->category == EPIC_CAT_NOTIFY) {
 		struct epic_std_service_ap_call *call = payload;
 		size_t call_size;
+		u32 command;
 		void *reply;
+		u16 group;
 		int ret;
 
 		if (payload_size < sizeof(*call))
 			return;
 
-		call_size = le32_to_cpu(call->len);
+		call_size = le32_to_cpu(call->call.data_len);
 		if (payload_size < sizeof(*call) + call_size)
 			return;
 
-		if (!service->ops->call)
+		group = le16_to_cpu(call->call.group);
+		command = le32_to_cpu(call->call.command);
+
+		/*
+		 * Command numbers are per group: a group-less .call handler
+		 * would take another group's call for a group 0 one. Without
+		 * call_v2 there is no handler for it, and AFK cannot guess a
+		 * reply, so it gets none, as a call without any handler.
+		 */
+		if (!service->ops->call_v2 && (group || !service->ops->call)) {
+			if (group)
+				dev_warn_ratelimited(ep->dcp->dev,
+						     "AFK[ep:%02x]: %s (chan:%u) apcall %u:%u has no handler, sending NO reply\n",
+						     ep->endpoint, service->ops->name,
+						     channel, group, command);
 			return;
+		}
 		reply = kzalloc(payload_size, GFP_KERNEL);
 		if (!reply)
 			return;
 
-		ret = service->ops->call(service, le32_to_cpu(call->type),
-					 payload + sizeof(*call), call_size,
-					 reply + sizeof(*call), call_size);
+		if (service->ops->call_v2)
+			ret = service->ops->call_v2(service, group, command,
+						    payload + sizeof(*call),
+						    call_size,
+						    reply + sizeof(*call),
+						    call_size);
+		else
+			ret = service->ops->call(service, command,
+						 payload + sizeof(*call),
+						 call_size,
+						 reply + sizeof(*call),
+						 call_size);
 		if (ret) {
 			dev_warn(ep->dcp->dev,
-				 "AFK[ep:%02x]: %s (chan:%u) apcall %u handler returned %d, sending NO reply\n",
+				 "AFK[ep:%02x]: %s (chan:%u) apcall %u:%u handler returned %d, sending NO reply\n",
 				 ep->endpoint, service->ops->name, channel,
-				 le32_to_cpu(call->type), ret);
+				 group, command, ret);
 			kfree(reply);
 			return;
 		}

drivers/gpu/drm/apple/afk.h

@@ -74,6 +74,8 @@ struct apple_epic_service_ops {
 	int (*call)(struct apple_epic_service *service, u32 idx,
 		    const void *data, size_t data_size, void *reply,
 		    size_t reply_size);
+	int (*call_v2)(struct apple_epic_service *service, u16 group, u32 command,
+		       const void *data, size_t size, void *reply, size_t room);
 	int (*report)(struct apple_epic_service *service, enum epic_subtype type,
 		      const void *data, size_t data_size);
 	void (*teardown)(struct apple_epic_service *service);

drivers/gpu/drm/apple/dptxep.c

@@ -691,7 +691,7 @@ static int dptxport_call(struct apple_epic_service *service, u32 idx,
 			 size_t reply_size)
 {
 	struct dptx_port *dptx = service->cookie;
-	trace_dptxport_apcall(dptx, idx, data_size);
+	trace_dptxport_apcall(dptx, 0, idx, data_size);
 	dev_dbg(service->ep->dcp->dev, "DPTXPort: APCALL %u (%zu bytes)\n",
 		 idx, data_size);
 	if (data_size)
@@ -836,11 +836,69 @@ static void dptxport_init(struct apple_epic_service *service, const char *name,
 	}
 }
 
+/*
+ * Group 1 calls 3 and 4 come around link (re)configuration, audio prepare
+ * included. They carry a lane count at +0x10 in (1, 3) and at +0x00 in
+ * (1, 4); the J700 code reads (1, 3) as drive settings with levels per
+ * lane from +0x20, and its group 0 GET (0, 4) has the count at +0x00.
+ * macOS 13 acks both with the request, (1, 3) with +0x00..0x03
+ * cleared and (1, 4) with +0x10..0x13 and +0x20 to the end cleared, so
+ * what DCP left there does not go back (42 of 42 traced pairs on t6020,
+ * 13.5 firmware: TV through a USB-C to HDMI adapter, Dell over TB).
+ */
+static int dptxport_call_group1(u32 command, const void *data,
+				size_t data_size, void *reply, size_t reply_size)
+{
+	size_t size = min(reply_size, data_size);
+
+	memcpy(reply, data, size);
+	if (command == 3) {
+		memset(reply, 0, min_t(size_t, size, 0x4));
+	} else if (size > 0x10) {
+		memset(reply + 0x10, 0, min_t(size_t, size - 0x10, 0x4));
+		if (size > 0x20)
+			memset(reply + 0x20, 0, size - 0x20);
+	}
+	return 0;
+}
+
+static int dptxport_group_call(struct apple_epic_service *service, u16 group,
+			       u32 command, const void *data, size_t size,
+			       void *reply, size_t room)
+{
+	struct dptx_port *dptx = service->cookie;
+
+	if (!group)
+		return dptxport_call(service, command, data, size, reply, room);
+
+	trace_dptxport_apcall(dptx, group, command, size);
+	dev_dbg(service->ep->dcp->dev, "DPTXPort: APCALL %u:%u (%zu bytes)\n",
+		group, command, size);
+	if (size)
+		print_hex_dump_debug("DPTXPort: apcall data: ",
+				     DUMP_PREFIX_OFFSET, 16, 1, data,
+				     min(size, (size_t)64), true);
+
+	if (group == 1 && (command == 3 || command == 4))
+		return dptxport_call_group1(command, data, size, reply, room);
+
+	/*
+	 * Echo it, as group 0 acks an unhandled call: no reply might stall
+	 * DCP's caller.
+	 */
+	dev_warn_ratelimited(service->ep->dcp->dev,
+			     "DPTXPort: unknown AP call %u:%u, echoing it\n",
+			     group, command);
+	memcpy(reply, data, min(room, size));
+	return 0;
+}
+
 static const struct apple_epic_service_ops dptxep_ops[] = {
 	{
 		.name = "AppleDCPDPTXRemotePort",
 		.init = dptxport_init,
 		.call = dptxport_call,
+		.call_v2 = dptxport_group_call,
 	},
 	{}
 };

drivers/gpu/drm/apple/trace.h

@@ -398,18 +398,21 @@ TRACE_EVENT(dptxport_init, TP_PROTO(struct apple_dcp *dcp, u64 unit),
 
 TRACE_EVENT(
 	dptxport_apcall,
-	TP_PROTO(struct dptx_port *dptx, int idx, size_t len),
-	TP_ARGS(dptx, idx, len),
+	TP_PROTO(struct dptx_port *dptx, u16 group, int idx, size_t len),
+	TP_ARGS(dptx, group, idx, len),
 
 	TP_STRUCT__entry(__string(devname, dev_name(dptx->service->ep->dcp->dev))
-			__field(u32, unit) __field(int, idx) __field(size_t, len)),
+			__field(u32, unit) __field(u16, group) __field(int, idx)
+			__field(size_t, len)),
 
 	TP_fast_assign(__assign_str(devname);
-		       __entry->unit = dptx->unit; __entry->idx = idx; __entry->len = len;),
+		       __entry->unit = dptx->unit; __entry->group = group;
+		       __entry->idx = idx; __entry->len = len;),
 
-	TP_printk("%s: dptx%d: AP Call %d (%s) with len %lu", __get_str(devname),
-		  __entry->unit,
-		  __entry->idx, show_dptxport_apcall(__entry->idx), __entry->len));
+	TP_printk("%s: dptx%d: AP Call %u:%d (%s) with len %lu", __get_str(devname),
+		  __entry->unit, __entry->group, __entry->idx,
+		  __entry->group ? "-" : show_dptxport_apcall(__entry->idx),
+		  __entry->len));
 
 TRACE_EVENT(
 	dptxport_validate_connection,