firewire: core: allocate workqueue to handle isochronous contexts in card

This commit adds a workqueue dedicated for isochronous context processing.

The workqueue is allocated per instance of fw_card structure to satisfy the
following characteristics descending from 1394 OHCI specification:

In 1394 OHCI specification, memory pages are reserved to each isochronous
context dedicated to DMA transmission. It allows to operate these
per-context pages concurrently. Software can schedule hardware interrupt
for several isochronous context to the same cycle, thus WQ_UNBOUND is
specified. Additionally, it is sleepable to operate the content of pages,
thus WQ_BH is not used.

The isochronous context delivers the packets with time stamp, thus
WQ_HIGHPRI is specified for semi real-time data such as IEC 61883-1/6
protocol implemented by ALSA firewire stack. The isochronous context is not
used by the implementation of SCSI over IEEE1394 protocol (sbp2), thus
WQ_MEM_RECLAIM is not specified.

It is useful for users to adjust cpu affinity of the workqueue depending
on their work loads, thus WQ_SYS is specified to expose the attributes to
user space.
Tested-by: Edmund Raile <edmund.raile@protonmail.com>
Link: https://lore.kernel.org/r/20240904125155.461886-2-o-takashi@sakamocchi.jpSigned-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

drivers/firewire/core-card.c

@@ -571,11 +571,30 @@ void fw_card_initialize(struct fw_card *card,
 }
 EXPORT_SYMBOL(fw_card_initialize);
 
-int fw_card_add(struct fw_card *card,
-		u32 max_receive, u32 link_speed, u64 guid)
+int fw_card_add(struct fw_card *card, u32 max_receive, u32 link_speed, u64 guid,
+		unsigned int supported_isoc_contexts)
 {
+	struct workqueue_struct *isoc_wq;
 	int ret;
 
+	// This workqueue should be:
+	//  * != WQ_BH			Sleepable.
+	//  * == WQ_UNBOUND		Any core can process data for isoc context. The
+	//				implementation of unit protocol could consumes the core
+	//				longer somehow.
+	//  * != WQ_MEM_RECLAIM		Not used for any backend of block device.
+	//  * == WQ_FREEZABLE		Isochronous communication is at regular interval in real
+	//				time, thus should be drained if possible at freeze phase.
+	//  * == WQ_HIGHPRI		High priority to process semi-realtime timestamped data.
+	//  * == WQ_SYSFS		Parameters are available via sysfs.
+	//  * max_active == n_it + n_ir	A hardIRQ could notify events for multiple isochronous
+	//				contexts if they are scheduled to the same cycle.
+	isoc_wq = alloc_workqueue("firewire-isoc-card%u",
+				  WQ_UNBOUND | WQ_FREEZABLE | WQ_HIGHPRI | WQ_SYSFS,
+				  supported_isoc_contexts, card->index);
+	if (!isoc_wq)
+		return -ENOMEM;
+
 	card->max_receive = max_receive;
 	card->link_speed = link_speed;
 	card->guid = guid;
@@ -584,9 +603,12 @@ int fw_card_add(struct fw_card *card,
 
 	generate_config_rom(card, tmp_config_rom);
 	ret = card->driver->enable(card, tmp_config_rom, config_rom_length);
-	if (ret < 0)
+	if (ret < 0) {
+		destroy_workqueue(isoc_wq);
 		return ret;
+	}
 
+	card->isoc_wq = isoc_wq;
 	list_add_tail(&card->link, &card_list);
 
 	return 0;
@@ -708,6 +730,8 @@ void fw_core_remove_card(struct fw_card *card)
 {
 	struct fw_card_driver dummy_driver = dummy_driver_template;
 
+	might_sleep();
+
 	card->driver->update_phy_reg(card, 4,
 				     PHY_LINK_ACTIVE | PHY_CONTENDER, 0);
 	fw_schedule_bus_reset(card, false, true);
@@ -719,6 +743,7 @@ void fw_core_remove_card(struct fw_card *card)
 	dummy_driver.free_iso_context	= card->driver->free_iso_context;
 	dummy_driver.stop_iso		= card->driver->stop_iso;
 	card->driver = &dummy_driver;
+	drain_workqueue(card->isoc_wq);
 
 	scoped_guard(spinlock_irqsave, &card->lock)
 		fw_destroy_nodes(card);
@@ -727,6 +752,8 @@ void fw_core_remove_card(struct fw_card *card)
 	fw_card_put(card);
 	wait_for_completion(&card->done);
 
+	destroy_workqueue(card->isoc_wq);
+
 	WARN_ON(!list_empty(&card->transaction_list));
 }
 EXPORT_SYMBOL(fw_core_remove_card);

drivers/firewire/core.h

@@ -115,8 +115,8 @@ struct fw_card_driver {
 
 void fw_card_initialize(struct fw_card *card,
 		const struct fw_card_driver *driver, struct device *device);
-int fw_card_add(struct fw_card *card,
-		u32 max_receive, u32 link_speed, u64 guid);
+int fw_card_add(struct fw_card *card, u32 max_receive, u32 link_speed, u64 guid,
+		unsigned int supported_isoc_contexts);
 void fw_core_remove_card(struct fw_card *card);
 int fw_compute_block_crc(__be32 *block);
 void fw_schedule_bm_work(struct fw_card *card, unsigned long delay);

drivers/firewire/ohci.c

@@ -3827,7 +3827,7 @@ static int pci_probe(struct pci_dev *dev,
 		goto fail_msi;
 	}
 
-	err = fw_card_add(&ohci->card, max_receive, link_speed, guid);
+	err = fw_card_add(&ohci->card, max_receive, link_speed, guid, ohci->n_it + ohci->n_ir);
 	if (err)
 		goto fail_irq;
 

include/linux/firewire.h

@@ -134,6 +134,8 @@ struct fw_card {
 	__be32 topology_map[(CSR_TOPOLOGY_MAP_END - CSR_TOPOLOGY_MAP) / 4];
 
 	__be32 maint_utility_register;
+
+	struct workqueue_struct *isoc_wq;
 };
 
 static inline struct fw_card *fw_card_get(struct fw_card *card)