From 72bf1441231ab421a380771e37a5c595493db178 Mon Sep 17 00:00:00 2001 From: Takashi Sakamoto Date: Sun, 15 Jun 2025 22:32:51 +0900 Subject: firewire: core: allocate workqueue for AR/AT request/response contexts Some tasklets (softIRQs) are still used as bottom-halves to handle events for 1394 OHCI AR/AT contexts. However, using softIRQs for IRQ bottom halves is generally discouraged today. This commit adds a per-fw_card workqueue to accommodate the behaviour specified by the 1394 OHCI specification. According to the 1394 OHCI specification, system memory pages are reserved for each asynchronous DMA context. This allows concurrent operation across contexts. In the 1394 OHCI PCI driver implementation, the hardware generates IRQs either upon receiving asynchronous packets from other nodes (incoming) or after completing transmission to them (outgoing). These independent events can occur in the same transmission cycle, therefore the max_active parameter for the workqueue is set to the total number of AR/AT contexts (=4). The WQ_UNBOUND flag is used to allow the work to be scheduled on any available core, since there is little CPU cache affinity benefit for the data. Each DMA context uses a circular descriptor list in system memory, allowing deferred data processing in software as long as buffer overrun are avoided. Since the overall operation is sleepable except for small atomic regions, WQ_BH is not used. As the descriptors contain timestamps, WQ_HIGHPRI is specified to support semi-real-time processing. The asynchronous context is also used by the SCSI over IEEE 1394 protocol implementation (sbp2), which can be part of memory reclaim paths. Therefore, WQ_MEM_RECLAIM is required. To allow uses to adjust CPU affinity according to workload, WQ_SYSFS is specified so that workqueue attributes are exposed to user space. Link: https://lore.kernel.org/r/20250615133253.433057-2-o-takashi@sakamocchi.jp Signed-off-by: Takashi Sakamoto --- include/linux/firewire.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux') diff --git a/include/linux/firewire.h b/include/linux/firewire.h index b632eec3ab52..c55b8e30e700 100644 --- a/include/linux/firewire.h +++ b/include/linux/firewire.h @@ -136,6 +136,7 @@ struct fw_card { __be32 maint_utility_register; struct workqueue_struct *isoc_wq; + struct workqueue_struct *async_wq; }; static inline struct fw_card *fw_card_get(struct fw_card *card) -- cgit v1.2.3 From aef6bcc0f278eba408751f8b3e0beae992e9faec Mon Sep 17 00:00:00 2001 From: Takashi Sakamoto Date: Sun, 15 Jun 2025 22:32:53 +0900 Subject: firewire: ohci: use workqueue to handle events of AT request/response contexts This commit adds a work item to handle events of 1394 OHCI AT request/response contexts, and queues the item to the specific workqueue. The call of struct fw_packet.callbaqck() is done in the workqueue when receiving acknowledgement to the asynchronous packet transferred to remote node. Link: https://lore.kernel.org/r/20250615133253.433057-4-o-takashi@sakamocchi.jp Signed-off-by: Takashi Sakamoto --- include/linux/firewire.h | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) (limited to 'include/linux') diff --git a/include/linux/firewire.h b/include/linux/firewire.h index c55b8e30e700..cceb70415ed2 100644 --- a/include/linux/firewire.h +++ b/include/linux/firewire.h @@ -308,8 +308,7 @@ struct fw_packet { * For successful transmission, the status code is the ack received * from the destination. Otherwise it is one of the juju-specific * rcodes: RCODE_SEND_ERROR, _CANCELLED, _BUSY, _GENERATION, _NO_ACK. - * The callback can be called from tasklet context and thus - * must never block. + * The callback can be called from workqueue and thus must never block. */ fw_packet_callback_t callback; int ack; @@ -382,6 +381,10 @@ void __fw_send_request(struct fw_card *card, struct fw_transaction *t, int tcode * * A variation of __fw_send_request() to generate callback for response subaction without time * stamp. + * + * The callback is invoked in the workqueue context in most cases. However, if an error is detected + * before queueing or the destination address refers to the local node, it is invoked in the + * current context instead. */ static inline void fw_send_request(struct fw_card *card, struct fw_transaction *t, int tcode, int destination_id, int generation, int speed, @@ -411,6 +414,10 @@ static inline void fw_send_request(struct fw_card *card, struct fw_transaction * * @callback_data: data to be passed to the transaction completion callback * * A variation of __fw_send_request() to generate callback for response subaction with time stamp. + * + * The callback is invoked in the workqueue context in most cases. However, if an error is detected + * before queueing or the destination address refers to the local node, it is invoked in the current + * context instead. */ static inline void fw_send_request_with_tstamp(struct fw_card *card, struct fw_transaction *t, int tcode, int destination_id, int generation, int speed, unsigned long long offset, -- cgit v1.2.3