idpf: compile singleq code only under default-n CONFIG_IDPF_SINGLEQ

Currently, all HW supporting idpf supports the singleq model, but none
of it advertises it by default, as splitq is supported and preferred
for multiple reasons. Still, this almost dead code often times adds
hotpath branches and redundant cacheline accesses.
While it can't currently be removed, add CONFIG_IDPF_SINGLEQ and build
the singleq code only when it's enabled manually. This corresponds to
-10 Kb of object code size and a good bunch of hotpath checks.
idpf_is_queue_model_split() works as a gate and compiles out to `true`
when the config option is disabled.

Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/Kconfig

@@ -384,17 +384,6 @@ config IGC_LEDS
 	  Optional support for controlling the NIC LED's with the netdev
 	  LED trigger.
 
-config IDPF
-	tristate "Intel(R) Infrastructure Data Path Function Support"
-	depends on PCI_MSI
-	select DIMLIB
-	select PAGE_POOL
-	select PAGE_POOL_STATS
-	help
-	  This driver supports Intel(R) Infrastructure Data Path Function
-	  devices.
-
-	  To compile this driver as a module, choose M here. The module
-	  will be called idpf.
+source "drivers/net/ethernet/intel/idpf/Kconfig"
 
 endif # NET_VENDOR_INTEL

drivers/net/ethernet/intel/idpf/Kconfig

@@ -0,0 +1,27 @@
+# SPDX-License-Identifier: GPL-2.0-only
+# Copyright (C) 2024 Intel Corporation
+
+config IDPF
+	tristate "Intel(R) Infrastructure Data Path Function Support"
+	depends on PCI_MSI
+	select DIMLIB
+	select PAGE_POOL
+	select PAGE_POOL_STATS
+	help
+	  This driver supports Intel(R) Infrastructure Data Path Function
+	  devices.
+
+	  To compile this driver as a module, choose M here. The module
+	  will be called idpf.
+
+if IDPF
+
+config IDPF_SINGLEQ
+	bool "idpf singleq support"
+	help
+	  This option enables support for legacy single Rx/Tx queues w/no
+	  completion and fill queues. Only enable if you have hardware which
+	  wants to work in this mode as it increases the driver size and adds
+	  runtme checks on hotpath.
+
+endif # IDPF

drivers/net/ethernet/intel/idpf/Makefile

@@ -12,7 +12,8 @@ idpf-y := \
 	idpf_ethtool.o		\
 	idpf_lib.o		\
 	idpf_main.o		\
-	idpf_singleq_txrx.o	\
 	idpf_txrx.o		\
 	idpf_virtchnl.o 	\
 	idpf_vf_dev.o
+
+idpf-$(CONFIG_IDPF_SINGLEQ)	+= idpf_singleq_txrx.o

drivers/net/ethernet/intel/idpf/idpf.h

@@ -599,7 +599,8 @@ struct idpf_adapter {
  */
 static inline int idpf_is_queue_model_split(u16 q_model)
 {
-	return q_model == VIRTCHNL2_QUEUE_MODEL_SPLIT;
+	return !IS_ENABLED(CONFIG_IDPF_SINGLEQ) ||
+	       q_model == VIRTCHNL2_QUEUE_MODEL_SPLIT;
 }
 
 #define idpf_is_cap_ena(adapter, field, flag) \

drivers/net/ethernet/intel/idpf/idpf_txrx.c

@@ -1309,7 +1309,7 @@ static void idpf_vport_calc_numq_per_grp(struct idpf_vport *vport,
 static void idpf_rxq_set_descids(const struct idpf_vport *vport,
 				 struct idpf_rx_queue *q)
 {
-	if (vport->rxq_model == VIRTCHNL2_QUEUE_MODEL_SPLIT) {
+	if (idpf_is_queue_model_split(vport->rxq_model)) {
 		q->rxdids = VIRTCHNL2_RXDID_2_FLEX_SPLITQ_M;
 	} else {
 		if (vport->base_rxd)

drivers/net/ethernet/intel/idpf/idpf_virtchnl.c

@@ -1256,12 +1256,12 @@ int idpf_send_create_vport_msg(struct idpf_adapter *adapter,
 	vport_msg->vport_type = cpu_to_le16(VIRTCHNL2_VPORT_TYPE_DEFAULT);
 	vport_msg->vport_index = cpu_to_le16(idx);
 
-	if (adapter->req_tx_splitq)
+	if (adapter->req_tx_splitq || !IS_ENABLED(CONFIG_IDPF_SINGLEQ))
 		vport_msg->txq_model = cpu_to_le16(VIRTCHNL2_QUEUE_MODEL_SPLIT);
 	else
 		vport_msg->txq_model = cpu_to_le16(VIRTCHNL2_QUEUE_MODEL_SINGLE);
 
-	if (adapter->req_rx_splitq)
+	if (adapter->req_rx_splitq || !IS_ENABLED(CONFIG_IDPF_SINGLEQ))
 		vport_msg->rxq_model = cpu_to_le16(VIRTCHNL2_QUEUE_MODEL_SPLIT);
 	else
 		vport_msg->rxq_model = cpu_to_le16(VIRTCHNL2_QUEUE_MODEL_SINGLE);
@@ -1323,10 +1323,17 @@ int idpf_check_supported_desc_ids(struct idpf_vport *vport)
 
 	vport_msg = adapter->vport_params_recvd[vport->idx];
 
+	if (!IS_ENABLED(CONFIG_IDPF_SINGLEQ) &&
+	    (vport_msg->rxq_model == VIRTCHNL2_QUEUE_MODEL_SINGLE ||
+	     vport_msg->txq_model == VIRTCHNL2_QUEUE_MODEL_SINGLE)) {
+		pci_err(adapter->pdev, "singleq mode requested, but not compiled-in\n");
+		return -EOPNOTSUPP;
+	}
+
 	rx_desc_ids = le64_to_cpu(vport_msg->rx_desc_ids);
 	tx_desc_ids = le64_to_cpu(vport_msg->tx_desc_ids);
 
-	if (vport->rxq_model == VIRTCHNL2_QUEUE_MODEL_SPLIT) {
+	if (idpf_is_queue_model_split(vport->rxq_model)) {
 		if (!(rx_desc_ids & VIRTCHNL2_RXDID_2_FLEX_SPLITQ_M)) {
 			dev_info(&adapter->pdev->dev, "Minimum RX descriptor support not provided, using the default\n");
 			vport_msg->rx_desc_ids = cpu_to_le64(VIRTCHNL2_RXDID_2_FLEX_SPLITQ_M);
@@ -1336,7 +1343,7 @@ int idpf_check_supported_desc_ids(struct idpf_vport *vport)
 			vport->base_rxd = true;
 	}
 
-	if (vport->txq_model != VIRTCHNL2_QUEUE_MODEL_SPLIT)
+	if (!idpf_is_queue_model_split(vport->txq_model))
 		return 0;
 
 	if ((tx_desc_ids & MIN_SUPPORT_TXDID) != MIN_SUPPORT_TXDID) {