firewire: use sleepable workqueue to handle 1394 OHCI IT/IR context events: test 1

[Edmund Raile <edmund.raile@xxxxxxxxxxxxxx>]

Hello Sakamoto-San, I very much appreciate the idea and effort to take on the tasklet conversion in small steps instead of all-at-once!

I also thank you for the CC, I'd like to be the testing canary for the coal mine of firewire ALSA with RME FireFace!
The ALSA mailing list is a bit overwhelming and I'll likely unsubscribe so a direct CC for anything I can test is a good idea.

Trying to apply patch 1 of 5 to mainline, your kernel tree appears to be out of sync with mainline!
It was missing b171e20 from 2009 and a7ecbe9 from 2022!
I hope nothing else important is missing!

Since in fw_card_initialize, ret is tested to be 0 we'd need an else instead, is this correct?

I edited these functions of patch 1, now everything applies just fine:

@@ -571,11 +571,28 @@ 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_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_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 +601,13 @@ 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)
 		list_add_tail(&card->link, &card_list);
+	else
+		destroy_workqueue(isoc_wq);
+
+	card->isoc_wq = isoc_wq;

 	mutex_unlock(&card_mutex);

 	return ret;
@@ -709,7 +729,9 @@ void fw_core_remove_card(struct fw_card *card)
 {
 	struct fw_card_driver dummy_driver = dummy_driver_template;
 	unsigned long flags;
 
+	might_sleep();
+
 	card->driver->update_phy_reg(card, 4,
 				     PHY_LINK_ACTIVE | PHY_CONTENDER, 0);
 	fw_schedule_bus_reset(card, false, true);
@@ -719,6 +741,7 @@ 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);
 
 	spin_lock_irqsave(&card->lock, flags);
 	fw_destroy_nodes(card);

Building a kernel with the patch produced 6.11.0-rc6-1-mainline-00019-g67784a74e258-dirty.
Testing it with TI XIO2213B and RME Fireface 800 so far > 1 hour reveals no issues at all.
ALSA streaming works fine:
  mpv --audio-device=alsa/sysdefault:CARD=Fireface800 Spor-Ignition.flac

Though I haven't the faintest clue how to measure CPU usage impact of the patch, it looks like it would be neglible.

As of finishing this, I noticed you released [2] https://lore.kernel.org/lkml/20240904125155.461886-1-o-takashi@xxxxxxxxxxxxx/T/
I'll get around to testing that one too, but tomorrow at the earliest.

Kind regards,
Edmund Raile.

Signed-off-by: Edmund Raile <edmund.raile@xxxxxxxxxxxxxx>
Tested-by: Edmund Raile <edmund.raile@xxxxxxxxxxxxxx>