isci: workaround port task scheduler starvation issue

There is a condition whereby TCs (task contexts) can jump to the head of
the round robin queue causing indefinite starvation of pending tasks.
Posting a TC to a suspended RNC (remote node context) causes the
hardware to select that task first, but since the RNC is suspended the
scheduler proceeds to the next task in the expected round robin fashion,
restoring TC arbitration fairness.

Signed-off-by: Tomasz Chudy <tomasz.chudy@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/scsi/isci/core/scic_port.h

@@ -147,23 +147,6 @@ enum sci_status scic_port_get_properties(
 	struct scic_sds_port *port,
 	struct scic_port_properties *properties);
 
-
-
-/**
- * scic_port_start() - This method will make the port ready for operation.
- *    Prior to calling the start method IO operation is not possible.
- * @port: This parameter specifies the port to be started.
- *
- * Indicate if the port was successfully started. SCI_SUCCESS This value is
- * returned if the port was successfully started. SCI_WARNING_ALREADY_IN_STATE
- * This value is returned if the port is in the process of starting.
- * SCI_FAILURE_INVALID_PORT This value is returned if the supplied port is not
- * valid. SCI_FAILURE_INVALID_STATE This value is returned if a start operation
- * can't be completed due to the state of port.
- */
-enum sci_status scic_port_start(
-	struct scic_sds_port *port);
-
 /**
  * scic_port_stop() - This method will make the port no longer ready for
  *    operation.  After invoking this method IO operation is not possible.

drivers/scsi/isci/core/scic_sds_controller.c

@@ -796,7 +796,11 @@ enum sci_status scic_sds_controller_stop_ports(struct scic_sds_controller *scic)
 	enum sci_status status = SCI_SUCCESS;
 
 	for (index = 0; index < scic->logical_port_entries; index++) {
-		port_status = scic_port_stop(&scic->port_table[index]);
+		struct scic_sds_port *sci_port = &scic->port_table[index];
+		SCI_BASE_PORT_HANDLER_T stop;
+
+		stop = sci_port->state_handlers->parent.stop_handler;
+		port_status = stop(&sci_port->parent);
 
 		if ((port_status != SCI_SUCCESS) &&
 		    (port_status != SCI_FAILURE_INVALID_STATE)) {
@@ -806,7 +810,7 @@ enum sci_status scic_sds_controller_stop_ports(struct scic_sds_controller *scic)
 				 "%s: Controller stop operation failed to "
 				 "stop port %d because of status %d.\n",
 				 __func__,
-				 scic->port_table[index].logical_port_index,
+				 sci_port->logical_port_index,
 				 port_status);
 		}
 	}
@@ -3003,7 +3007,7 @@ static enum sci_status scic_sds_controller_initialized_state_start_handler(
 		scic_sds_controller_ram_initialization(this_controller);
 	}
 
-	if (SCI_SUCCESS == result) {
+	if (result == SCI_SUCCESS) {
 		/* Build the TCi free pool */
 		sci_pool_initialize(this_controller->tci_pool);
 		for (index = 0; index < this_controller->task_context_entries; index++) {
@@ -3017,7 +3021,7 @@ static enum sci_status scic_sds_controller_initialized_state_start_handler(
 			);
 	}
 
-	if (SCI_SUCCESS == result) {
+	if (result == SCI_SUCCESS) {
 		/*
 		 * Before anything else lets make sure we will not be interrupted
 		 * by the hardware. */
@@ -3036,7 +3040,15 @@ static enum sci_status scic_sds_controller_initialized_state_start_handler(
 		scic_sds_controller_initialize_unsolicited_frame_queue(this_controller);
 	}
 
-	if (SCI_SUCCESS == result) {
+	/* Start all of the ports on this controller */
+	for (index = 0; index < this_controller->logical_port_entries &&
+			result == SCI_SUCCESS; index++) {
+		struct scic_sds_port *sci_port = &this_controller->port_table[index];
+
+		result = sci_port->state_handlers->parent.start_handler(&sci_port->parent);
+	}
+
+	if (result == SCI_SUCCESS) {
 		scic_sds_controller_start_next_phy(this_controller);
 
 		isci_event_timer_start(this_controller,

drivers/scsi/isci/core/scic_sds_port.c

@@ -67,6 +67,7 @@
 #include "scic_sds_remote_node_context.h"
 #include "scic_sds_request.h"
 #include "sci_environment.h"
+#include "scic_sds_controller_registers.h"
 
 
 static void scic_sds_port_invalid_link_up(
@@ -78,6 +79,7 @@ static void scic_sds_port_timeout_handler(
 #define SCIC_SDS_PORT_MAX_TIMER_COUNT  (SCI_MAX_PORTS)
 
 #define SCIC_SDS_PORT_HARD_RESET_TIMEOUT  (1000)
+#define SCU_DUMMY_INDEX    (0xFFFF)
 
 void sci_base_port_construct(
 	struct sci_base_port *base_port,
@@ -474,67 +476,131 @@ void scic_sds_port_get_attached_protocols(
 }
 
 /**
- * This method returns the amount of memory requred for a port object.
+ * scic_sds_port_construct_dummy_rnc() - create dummy rnc for si workaround
  *
- * u32
- */
-
-/**
- * This method returns the minimum number of timers required for all port
- *    objects.
+ * @sci_port: logical port on which we need to create the remote node context
+ * @rni: remote node index for this remote node context.
  *
- * u32
+ * This routine will construct a dummy remote node context data structure
+ * This structure will be posted to the hardware to work around a scheduler
+ * error in the hardware.
  */
+void scic_sds_port_construct_dummy_rnc(struct scic_sds_port *sci_port, u16 rni)
+{
+	union scu_remote_node_context *rnc;
 
-/**
- * This method returns the maximum number of timers required for all port
- *    objects.
- *
- * u32
- */
+	rnc = &sci_port->owning_controller->remote_node_context_table[rni];
+
+	memset(rnc, 0, sizeof(union scu_remote_node_context));
+
+	rnc->ssp.remote_sas_address_hi = 0;
+	rnc->ssp.remote_sas_address_lo = 0;
+
+	rnc->ssp.remote_node_index = rni;
+	rnc->ssp.remote_node_port_width = 1;
+	rnc->ssp.logical_port_index = sci_port->physical_port_index;
+
+	rnc->ssp.nexus_loss_timer_enable = false;
+	rnc->ssp.check_bit = false;
+	rnc->ssp.is_valid = true;
+	rnc->ssp.is_remote_node_context = true;
+	rnc->ssp.function_number = 0;
+	rnc->ssp.arbitration_wait_time = 0;
+}
 
 /**
+ * scic_sds_port_construct_dummy_task() - create dummy task for si workaround
+ * @sci_port The logical port on which we need to create the
+ *            remote node context.
+ *            context.
+ * @tci The remote node index for this remote node context.
  *
- * @this_port:
- * @port_index:
- *
+ * This routine will construct a dummy task context data structure.  This
+ * structure will be posted to the hardwre to work around a scheduler error
+ * in the hardware.
  *
  */
-void scic_sds_port_construct(
-	struct scic_sds_port *this_port,
-	u8 port_index,
-	struct scic_sds_controller *owning_controller)
+void scic_sds_port_construct_dummy_task(struct scic_sds_port *sci_port, u16 tci)
+{
+	struct scu_task_context *task_context;
+
+	task_context = scic_sds_controller_get_task_context_buffer(sci_port->owning_controller, tci);
+
+	memset(task_context, 0, sizeof(struct scu_task_context));
+
+	task_context->abort = 0;
+	task_context->priority = 0;
+	task_context->initiator_request = 1;
+	task_context->connection_rate = 1;
+	task_context->protocol_engine_index = 0;
+	task_context->logical_port_index = sci_port->physical_port_index;
+	task_context->protocol_type = SCU_TASK_CONTEXT_PROTOCOL_SSP;
+	task_context->task_index = scic_sds_io_tag_get_index(tci);
+	task_context->valid = SCU_TASK_CONTEXT_VALID;
+	task_context->context_type = SCU_TASK_CONTEXT_TYPE;
+
+	task_context->remote_node_index = sci_port->reserved_rni;
+	task_context->command_code = 0;
+
+	task_context->link_layer_control = 0;
+	task_context->do_not_dma_ssp_good_response = 1;
+	task_context->strict_ordering = 0;
+	task_context->control_frame = 0;
+	task_context->timeout_enable = 0;
+	task_context->block_guard_enable = 0;
+
+	task_context->address_modifier = 0;
+
+	task_context->task_phase = 0x01;
+}
+
+void scic_sds_port_destroy_dummy_resources(struct scic_sds_port *sci_port)
+{
+	struct scic_sds_controller *scic = sci_port->owning_controller;
+
+	if (sci_port->reserved_tci != SCU_DUMMY_INDEX)
+		scic_controller_free_io_tag(scic, sci_port->reserved_tci);
+
+	if (sci_port->reserved_rni != SCU_DUMMY_INDEX)
+		scic_sds_remote_node_table_release_remote_node_index(&scic->available_remote_nodes,
+								     1, sci_port->reserved_rni);
+
+	sci_port->reserved_rni = SCU_DUMMY_INDEX;
+	sci_port->reserved_tci = SCU_DUMMY_INDEX;
+}
+
+void scic_sds_port_construct(struct scic_sds_port *sci_port, u8 port_index,
+			     struct scic_sds_controller *scic)
 {
 	u32 index;
 
-	sci_base_port_construct(
-		&this_port->parent,
-		scic_sds_port_state_table
-		);
+	sci_base_port_construct(&sci_port->parent, scic_sds_port_state_table);
 
 	sci_base_state_machine_construct(
-		scic_sds_port_get_ready_substate_machine(this_port),
-		&this_port->parent.parent,
+		scic_sds_port_get_ready_substate_machine(sci_port),
+		&sci_port->parent.parent,
 		scic_sds_port_ready_substate_table,
 		SCIC_SDS_PORT_READY_SUBSTATE_WAITING
 		);
 
-	this_port->logical_port_index  = SCIC_SDS_DUMMY_PORT;
-	this_port->physical_port_index = port_index;
-	this_port->active_phy_mask     = 0;
+	sci_port->logical_port_index  = SCIC_SDS_DUMMY_PORT;
+	sci_port->physical_port_index = port_index;
+	sci_port->active_phy_mask     = 0;
 
-	this_port->owning_controller = owning_controller;
+	sci_port->owning_controller = scic;
 
-	this_port->started_request_count = 0;
-	this_port->assigned_device_count = 0;
+	sci_port->started_request_count = 0;
+	sci_port->assigned_device_count = 0;
 
-	this_port->timer_handle = NULL;
+	sci_port->reserved_rni = SCU_DUMMY_INDEX;
+	sci_port->reserved_tci = SCU_DUMMY_INDEX;
 
-	this_port->port_task_scheduler_registers = NULL;
+	sci_port->timer_handle = NULL;
 
-	for (index = 0; index < SCI_MAX_PHYS; index++) {
-		this_port->phy_table[index] = NULL;
-	}
+	sci_port->port_task_scheduler_registers = NULL;
+
+	for (index = 0; index < SCI_MAX_PHYS; index++)
+		sci_port->phy_table[index] = NULL;
 }
 
 /**
@@ -634,19 +700,11 @@ void scic_sds_port_general_link_up_handler(
 	}
 }
 
-
-enum sci_status scic_port_start(struct scic_sds_port *port)
-{
-	return port->state_handlers->parent.start_handler(&port->parent);
-}
-
-
 enum sci_status scic_port_stop(struct scic_sds_port *port)
 {
 	return port->state_handlers->parent.stop_handler(&port->parent);
 }
 
-
 enum sci_status scic_port_get_properties(
 	struct scic_sds_port *port,
 	struct scic_port_properties *prop)
@@ -1541,6 +1599,58 @@ static void scic_sds_port_suspend_port_task_scheduler(
 	scu_port_task_scheduler_write(this_port, control, pts_control_value);
 }
 
+/**
+ * scic_sds_port_post_dummy_request() - post dummy/workaround request
+ * @sci_port: port to post task
+ *
+ * Prevent the hardware scheduler from posting new requests to the front
+ * of the scheduler queue causing a starvation problem for currently
+ * ongoing requests.
+ *
+ */
+void scic_sds_port_post_dummy_request(struct scic_sds_port *sci_port)
+{
+	u32 command;
+	struct scu_task_context *task_context;
+	struct scic_sds_controller *scic = sci_port->owning_controller;
+	u16 tci = sci_port->reserved_tci;
+
+	task_context = scic_sds_controller_get_task_context_buffer(scic, tci);
+
+	task_context->abort = 0;
+
+	command = SCU_CONTEXT_COMMAND_REQUEST_TYPE_POST_TC |
+		  sci_port->physical_port_index << SCU_CONTEXT_COMMAND_LOGICAL_PORT_SHIFT |
+		  tci;
+
+	scic_sds_controller_post_request(scic, command);
+}
+
+/**
+ * This routine will abort the dummy request.  This will alow the hardware to
+ * power down parts of the silicon to save power.
+ *
+ * @sci_port: The port on which the task must be aborted.
+ *
+ */
+void scic_sds_port_abort_dummy_request(struct scic_sds_port *sci_port)
+{
+	struct scic_sds_controller *scic = sci_port->owning_controller;
+	u16 tci = sci_port->reserved_tci;
+	struct scu_task_context *tc;
+	u32 command;
+
+	tc = scic_sds_controller_get_task_context_buffer(scic, tci);
+
+	tc->abort = 1;
+
+	command = SCU_CONTEXT_COMMAND_REQUEST_POST_TC_ABORT |
+		  sci_port->physical_port_index << SCU_CONTEXT_COMMAND_LOGICAL_PORT_SHIFT |
+		  tci;
+
+	scic_sds_controller_post_request(scic, command);
+}
+
 /**
  *
  * @this_port: This is the struct scic_sds_port object to resume.
@@ -1584,6 +1694,12 @@ static void scic_sds_port_ready_substate_waiting_enter(
 
 	scic_sds_port_suspend_port_task_scheduler(this_port);
 
+	/* Kill the dummy task for this port if it has not yet posted
+	 * the hardware will treat this as a NOP and just return abort
+	 * complete.
+	 */
+	scic_sds_port_abort_dummy_request(this_port);
+
 	this_port->not_ready_reason = SCIC_PORT_NOT_READY_NO_ACTIVE_PHYS;
 
 	if (this_port->active_phy_mask != 0) {
@@ -1629,6 +1745,11 @@ static void scic_sds_port_ready_substate_operational_enter(
 	scic_sds_port_update_viit_entry(this_port);
 
 	scic_sds_port_resume_port_task_scheduler(this_port);
+
+	/* Post the dummy task for the port so the hardware can schedule
+	 * io correctly
+	 */
+	scic_sds_port_post_dummy_request(this_port);
 }
 
 /**
@@ -2062,6 +2183,7 @@ static enum sci_status scic_sds_port_general_complete_io_handler(
  * **************************************************************************** */
 
 /**
+ * scic_sds_port_stopped_state_start_handler() - stop a port from "started"
  *
  * @port: This is the struct sci_base_port object which is cast into a struct scic_sds_port
  *    object.
@@ -2075,13 +2197,14 @@ static enum sci_status scic_sds_port_general_complete_io_handler(
  * start request is successful and the struct scic_sds_port object has transitioned to
  * the SCI_BASE_PORT_STATE_READY.
  */
-static enum sci_status scic_sds_port_stopped_state_start_handler(
-	struct sci_base_port *port)
+static enum sci_status scic_sds_port_stopped_state_start_handler(struct sci_base_port *base_port)
 {
+	struct scic_sds_port *sci_port = container_of(base_port, typeof(*sci_port), parent);
+	struct scic_sds_controller *scic = sci_port->owning_controller;
+	enum sci_status status = SCI_SUCCESS;
 	u32 phy_mask;
-	struct scic_sds_port *this_port = (struct scic_sds_port *)port;
 
-	if (this_port->assigned_device_count > 0) {
+	if (sci_port->assigned_device_count > 0) {
 		/*
 		 * / @todo This is a start failure operation because there are still
 		 * /       devices assigned to this port.  There must be no devices
@@ -2089,22 +2212,56 @@ static enum sci_status scic_sds_port_stopped_state_start_handler(
 		return SCI_FAILURE_UNSUPPORTED_PORT_CONFIGURATION;
 	}
 
-	phy_mask = scic_sds_port_get_phys(this_port);
+	sci_port->timer_handle = isci_event_timer_create(scic,
+							 scic_sds_port_timeout_handler,
+							 sci_port);
 
-	/*
-	 * There are one or more phys assigned to this port.  Make sure
-	 * the port's phy mask is in fact legal and supported by the
-	 * silicon. */
-	if (scic_sds_port_is_phy_mask_valid(this_port, phy_mask) == true) {
-		sci_base_state_machine_change_state(
-			scic_sds_port_get_base_state_machine(this_port),
-			SCI_BASE_PORT_STATE_READY
-			);
+	if (!sci_port->timer_handle)
+		return SCI_FAILURE_INSUFFICIENT_RESOURCES;
 
-		return SCI_SUCCESS;
+	if (sci_port->reserved_rni == SCU_DUMMY_INDEX) {
+		u16 rni = scic_sds_remote_node_table_allocate_remote_node(&scic->available_remote_nodes, 1);
+
+		if (rni != SCU_DUMMY_INDEX)
+			scic_sds_port_construct_dummy_rnc(sci_port, rni);
+		else
+			status = SCI_FAILURE_INSUFFICIENT_RESOURCES;
+		sci_port->reserved_rni = rni;
+	}
+
+	if (sci_port->reserved_tci == SCU_DUMMY_INDEX) {
+		/* Allocate a TCI and remove the sequence nibble */
+		u16 tci = scic_controller_allocate_io_tag(scic);
+
+		if (tci != SCU_DUMMY_INDEX)
+			scic_sds_port_construct_dummy_task(sci_port, tci);
+		else
+			status = SCI_FAILURE_INSUFFICIENT_RESOURCES;
+		sci_port->reserved_tci = tci;
+	}
+
+	if (status == SCI_SUCCESS) {
+		phy_mask = scic_sds_port_get_phys(sci_port);
+
+		/*
+		 * There are one or more phys assigned to this port.  Make sure
+		 * the port's phy mask is in fact legal and supported by the
+		 * silicon.
+		 */
+		if (scic_sds_port_is_phy_mask_valid(sci_port, phy_mask) == true) {
+			sci_base_state_machine_change_state(
+				scic_sds_port_get_base_state_machine(sci_port),
+				SCI_BASE_PORT_STATE_READY);
+
+			return SCI_SUCCESS;
+		} else
+			status = SCI_FAILURE;
 	}
 
-	return SCI_FAILURE_UNSUPPORTED_PORT_CONFIGURATION;
+	if (status != SCI_SUCCESS)
+		scic_sds_port_destroy_dummy_resources(sci_port);
+
+	return status;
 }
 
 /**
@@ -2467,6 +2624,52 @@ static void scic_sds_port_disable_port_task_scheduler(
 	scu_port_task_scheduler_write(this_port, control, pts_control_value);
 }
 
+void scic_sds_port_post_dummy_remote_node(struct scic_sds_port *sci_port)
+{
+	struct scic_sds_controller *scic = sci_port->owning_controller;
+	u8 phys_index = sci_port->physical_port_index;
+	union scu_remote_node_context *rnc;
+	u16 rni = sci_port->reserved_rni;
+	u32 command;
+
+	rnc = &scic->remote_node_context_table[rni];
+	rnc->ssp.is_valid = true;
+
+	command = SCU_CONTEXT_COMMAND_POST_RNC_32 |
+		  phys_index << SCU_CONTEXT_COMMAND_LOGICAL_PORT_SHIFT | rni;
+
+	scic_sds_controller_post_request(scic, command);
+
+	/* ensure hardware has seen the post rnc command and give it
+	 * ample time to act before sending the suspend
+	 */
+	SMU_ISR_READ(scic); /* flush */
+	udelay(10);
+
+	command = SCU_CONTEXT_COMMAND_POST_RNC_SUSPEND_TX_RX |
+		  phys_index << SCU_CONTEXT_COMMAND_LOGICAL_PORT_SHIFT | rni;
+
+	scic_sds_controller_post_request(scic, command);
+}
+
+void scic_sds_port_invalidate_dummy_remote_node(struct scic_sds_port *sci_port)
+{
+	struct scic_sds_controller *scic = sci_port->owning_controller;
+	u8 phys_index = sci_port->physical_port_index;
+	union scu_remote_node_context *rnc;
+	u16 rni = sci_port->reserved_rni;
+	u32 command;
+
+	rnc = &scic->remote_node_context_table[rni];
+
+	rnc->ssp.is_valid = false;
+
+	command = SCU_CONTEXT_COMMAND_POST_RNC_INVALIDATE |
+		  phys_index << SCU_CONTEXT_COMMAND_LOGICAL_PORT_SHIFT | rni;
+
+	scic_sds_controller_post_request(scic, command);
+}
+
 /*
  * ******************************************************************************
  * *  PORT STATE METHODS
@@ -2562,6 +2765,9 @@ static void scic_sds_port_ready_state_enter(
 			);
 	}
 
+	/* Post and suspend the dummy remote node context for this port. */
+	scic_sds_port_post_dummy_remote_node(this_port);
+
 	/* Start the ready substate machine */
 	sci_base_state_machine_start(
 		scic_sds_port_get_ready_substate_machine(this_port)
@@ -2583,6 +2789,8 @@ static void scic_sds_port_ready_state_exit(
 	this_port = (struct scic_sds_port *)object;
 
 	sci_base_state_machine_stop(&this_port->ready_substate_machine);
+
+	scic_sds_port_invalidate_dummy_remote_node(this_port);
 }
 
 /**
@@ -2663,6 +2871,8 @@ static void scic_sds_port_stopping_state_exit(
 		scic_sds_port_get_controller(this_port),
 		this_port->timer_handle
 		);
+
+	scic_sds_port_destroy_dummy_resources(this_port);
 }
 
 /**

drivers/scsi/isci/core/scic_sds_port.h

@@ -72,6 +72,12 @@
 
 #define SCIC_SDS_DUMMY_PORT   0xFF
 
+/**
+ * This constant defines the value utilized by SCI Components to indicate
+ * an invalid handle.
+ */
+#define SCI_INVALID_HANDLE 0x0
+
 /**
  * enum SCIC_SDS_PORT_READY_SUBSTATES -
  *
@@ -134,6 +140,9 @@ struct scic_sds_port {
 	 */
 	u8 active_phy_mask;
 
+	u16 reserved_rni;
+	u16 reserved_tci;
+
 	/**
 	 * This field contains the count of the io requests started on this port
 	 * object.  It is used to control controller shutdown.

drivers/scsi/isci/host.c

@@ -381,7 +381,6 @@ int isci_host_init(struct isci_host *isci_host)
 	int index = 0;
 	enum sci_status status;
 	struct scic_sds_controller *controller;
-	struct scic_sds_port *scic_port;
 	union scic_oem_parameters scic_oem_params;
 	union scic_user_parameters scic_user_params;
 
@@ -517,11 +516,5 @@ int isci_host_init(struct isci_host *isci_host)
 	for (index = 0; index < SCI_MAX_PHYS; index++)
 		isci_phy_init(&isci_host->phys[index], isci_host, index);
 
-	/* Start the ports */
-	for (index = 0; index < SCI_MAX_PORTS; index++) {
-		scic_controller_get_port_handle(controller, index, &scic_port);
-		scic_port_start(scic_port);
-	}
-
 	return 0;
 }