firewire: ohci: use threaded IRQ handler to handle SelfIDComplete event

The first step  maintaining the bus topology is to handle SelfIDComplete
event. This event occurs after initiating bus reset when 1394 OHCI link
layer is enabled, or when the bus topology changes (e.g. when a device is
added). Because enumeration of the selfID sequence can take some time, it
should be processed in a bottom half.

Currently, this is done in a module-local workqueue with the
WQ_MEM_RECLAIM flag, to allow invocation during memory reclaim paths. A
threaded IRQ handler is a preferable alternative, as it eliminates the
need to manage workqueue attributes manually.

Although SelfIDComplete events are not so frequent in normal usage,
handling them correctly is critical for proper bus topology management.
This commit switches SelfIDComplete handling to a threaded IRQ handler.

Link: https://lore.kernel.org/r/20250823030954.268412-3-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

Author: takaswie

drivers/firewire/ohci.c

@@ -760,7 +760,7 @@ static __le32 *handle_ar_packet(struct ar_context *ctx, __le32 *buffer)
 	 *
 	 * Alas some chips sometimes emit bus reset packets with a
 	 * wrong generation.  We set the correct generation for these
-	 * at a slightly incorrect time (in bus_reset_work).
+	 * at a slightly incorrect time (in handle_selfid_complete_event).
 	 */
 	if (evt == OHCI1394_evt_bus_reset) {
 		if (!(ohci->quirks & QUIRK_RESET_PACKET))
@@ -1830,9 +1830,9 @@ static int find_and_insert_self_id(struct fw_ohci *ohci, int self_id_count)
 	return self_id_count;
 }
 
-static void bus_reset_work(struct work_struct *work)
+static irqreturn_t handle_selfid_complete_event(int irq, void *data)
 {
-	struct fw_ohci *ohci = from_work(ohci, work, bus_reset_work);
+	struct fw_ohci *ohci = data;
 	int self_id_count, generation, new_generation, i, j;
 	u32 reg, quadlet;
 	void *free_rom = NULL;
@@ -1843,11 +1843,11 @@ static void bus_reset_work(struct work_struct *work)
 	if (!(reg & OHCI1394_NodeID_idValid)) {
 		ohci_notice(ohci,
 			    "node ID not valid, new bus reset in progress\n");
-		return;
+		goto end;
 	}
 	if ((reg & OHCI1394_NodeID_nodeNumber) == 63) {
 		ohci_notice(ohci, "malconfigured bus\n");
-		return;
+		goto end;
 	}
 	ohci->node_id = reg & (OHCI1394_NodeID_busNumber |
 			       OHCI1394_NodeID_nodeNumber);
@@ -1861,7 +1861,7 @@ static void bus_reset_work(struct work_struct *work)
 	reg = reg_read(ohci, OHCI1394_SelfIDCount);
 	if (ohci1394_self_id_count_is_error(reg)) {
 		ohci_notice(ohci, "self ID receive error\n");
-		return;
+		goto end;
 	}
 
 	trace_self_id_complete(ohci->card.index, reg, ohci->self_id, has_be_header_quirk(ohci));
@@ -1876,7 +1876,7 @@ static void bus_reset_work(struct work_struct *work)
 
 	if (self_id_count > 252) {
 		ohci_notice(ohci, "bad selfIDSize (%08x)\n", reg);
-		return;
+		goto end;
 	}
 
 	quadlet = cond_le32_to_cpu(ohci->self_id[0], has_be_header_quirk(ohci));
@@ -1903,7 +1903,7 @@ static void bus_reset_work(struct work_struct *work)
 
 			ohci_notice(ohci, "bad self ID %d/%d (%08x != ~%08x)\n",
 				    j, self_id_count, id, id2);
-			return;
+			goto end;
 		}
 		ohci->self_id_buffer[j] = id;
 	}
@@ -1913,13 +1913,13 @@ static void bus_reset_work(struct work_struct *work)
 		if (self_id_count < 0) {
 			ohci_notice(ohci,
 				    "could not construct local self ID\n");
-			return;
+			goto end;
 		}
 	}
 
 	if (self_id_count == 0) {
 		ohci_notice(ohci, "no self IDs\n");
-		return;
+		goto end;
 	}
 	rmb();
 
@@ -1941,7 +1941,7 @@ static void bus_reset_work(struct work_struct *work)
 	new_generation = ohci1394_self_id_count_get_generation(reg);
 	if (new_generation != generation) {
 		ohci_notice(ohci, "new bus reset, discarding self ids\n");
-		return;
+		goto end;
 	}
 
 	// FIXME: Document how the locking works.
@@ -2002,6 +2002,8 @@ static void bus_reset_work(struct work_struct *work)
 				 self_id_count, ohci->self_id_buffer,
 				 ohci->csr_state_setclear_abdicate);
 	ohci->csr_state_setclear_abdicate = false;
+end:
+	return IRQ_HANDLED;
 }
 
 static irqreturn_t irq_handler(int irq, void *data)
@@ -2023,13 +2025,10 @@ static irqreturn_t irq_handler(int irq, void *data)
 		  event & ~(OHCI1394_busReset | OHCI1394_postedWriteErr));
 	trace_irqs(ohci->card.index, event);
 
-	// The flag is masked again at bus_reset_work() scheduled by selfID event.
+	// The flag is masked again at handle_selfid_complete_event() scheduled by selfID event.
 	if (event & OHCI1394_busReset)
 		reg_write(ohci, OHCI1394_IntMaskClear, OHCI1394_busReset);
 
-	if (event & OHCI1394_selfIDComplete)
-		queue_work(selfid_workqueue, &ohci->bus_reset_work);
-
 	if (event & OHCI1394_RQPkt)
 		queue_work(ohci->card.async_wq, &ohci->ar_request_ctx.work);
 
@@ -2100,7 +2099,10 @@ static irqreturn_t irq_handler(int irq, void *data)
 	} else
 		flush_writes(ohci);
 
-	return IRQ_HANDLED;
+	if (event & OHCI1394_selfIDComplete)
+		return IRQ_WAKE_THREAD;
+	else
+		return IRQ_HANDLED;
 }
 
 static int software_reset(struct fw_ohci *ohci)
@@ -2413,7 +2415,7 @@ static int ohci_set_config_rom(struct fw_card *card,
 	 * then set up the real values for the two registers.
 	 *
 	 * We use ohci->lock to avoid racing with the code that sets
-	 * ohci->next_config_rom to NULL (see bus_reset_work).
+	 * ohci->next_config_rom to NULL (see handle_selfid_complete_event).
 	 */
 
 	next_config_rom = dmam_alloc_coherent(ohci->card.device, CONFIG_ROM_SIZE,
@@ -3620,7 +3622,9 @@ static int pci_probe(struct pci_dev *dev,
 		goto fail_msi;
 	}
 
-	err = request_threaded_irq(irq, irq_handler, NULL,
+	// IRQF_ONESHOT is not applied so that any events are handled in the hardIRQ handler during
+	// invoking the threaded IRQ handler for SelfIDComplete event.
+	err = request_threaded_irq(irq, irq_handler, handle_selfid_complete_event,
 				   pci_dev_msi_enabled(dev) ? 0 : IRQF_SHARED, ohci_driver_name,
 				   ohci);
 	if (err < 0) {