firewire: core: use spin lock specific to timer for split transaction

At present the parameters to compute timeout time for split transaction is
protected by card-wide spin lock, while it is not necessarily convenient
in a point to narrower critical section.

This commit adds and uses another spin lock specific for the purpose.

Link: https://lore.kernel.org/r/20250915234747.915922-6-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

diff --git a/drivers/firewire/core-card.c b/drivers/firewire/core-card.c
index 39f9500..9649539 100644 (file)
--- a/drivers/firewire/core-card.c
+++ b/drivers/firewire/core-card.c
@@ -550,10 +550,12 @@ void fw_card_initialize(struct fw_card *card,
        INIT_LIST_HEAD(&card->transactions.list);
        spin_lock_init(&card->transactions.lock);
 
-       card->split_timeout_hi = DEFAULT_SPLIT_TIMEOUT / 8000;
-       card->split_timeout_lo = (DEFAULT_SPLIT_TIMEOUT % 8000) << 19;
-       card->split_timeout_cycles = DEFAULT_SPLIT_TIMEOUT;
-       card->split_timeout_jiffies = isoc_cycles_to_jiffies(DEFAULT_SPLIT_TIMEOUT);
+       card->split_timeout.hi = DEFAULT_SPLIT_TIMEOUT / 8000;
+       card->split_timeout.lo = (DEFAULT_SPLIT_TIMEOUT % 8000) << 19;
+       card->split_timeout.cycles = DEFAULT_SPLIT_TIMEOUT;
+       card->split_timeout.jiffies = isoc_cycles_to_jiffies(DEFAULT_SPLIT_TIMEOUT);
+       spin_lock_init(&card->split_timeout.lock);
+
        card->color = 0;
        card->broadcast_channel = BROADCAST_CHANNEL_INITIAL;
 

diff --git a/drivers/firewire/core-transaction.c b/drivers/firewire/core-transaction.c
index 5366d8a..dd3656a 100644 (file)
--- a/drivers/firewire/core-transaction.c
+++ b/drivers/firewire/core-transaction.c
@@ -137,14 +137,18 @@ static void split_transaction_timeout_callback(struct timer_list *timer)
 static void start_split_transaction_timeout(struct fw_transaction *t,
                                            struct fw_card *card)
 {
-       guard(spinlock_irqsave)(&card->lock);
+       unsigned long delta;
 
        if (list_empty(&t->link) || WARN_ON(t->is_split_transaction))
                return;
 
        t->is_split_transaction = true;
-       mod_timer(&t->split_timeout_timer,
-                 jiffies + card->split_timeout_jiffies);
+
+       // NOTE: This can be without irqsave when we can guarantee that __fw_send_request() for
+       // local destination never runs in any type of IRQ context.
+       scoped_guard(spinlock_irqsave, &card->split_timeout.lock)
+               delta = card->split_timeout.jiffies;
+       mod_timer(&t->split_timeout_timer, jiffies + delta);
 }
 
 static u32 compute_split_timeout_timestamp(struct fw_card *card, u32 request_timestamp);
@@ -164,8 +168,12 @@ static void transmit_complete_callback(struct fw_packet *packet,
                break;
        case ACK_PENDING:
        {
-               t->split_timeout_cycle =
-                       compute_split_timeout_timestamp(card, packet->timestamp) & 0xffff;
+               // NOTE: This can be without irqsave when we can guarantee that __fw_send_request() for
+               // local destination never runs in any type of IRQ context.
+               scoped_guard(spinlock_irqsave, &card->split_timeout.lock) {
+                       t->split_timeout_cycle =
+                               compute_split_timeout_timestamp(card, packet->timestamp) & 0xffff;
+               }
                start_split_transaction_timeout(t, card);
                break;
        }
@@ -790,11 +798,14 @@ EXPORT_SYMBOL(fw_fill_response);
 
 static u32 compute_split_timeout_timestamp(struct fw_card *card,
                                           u32 request_timestamp)
+__must_hold(&card->split_timeout.lock)
 {
        unsigned int cycles;
        u32 timestamp;
 
-       cycles = card->split_timeout_cycles;
+       lockdep_assert_held(&card->split_timeout.lock);
+
+       cycles = card->split_timeout.cycles;
        cycles += request_timestamp & 0x1fff;
 
        timestamp = request_timestamp & ~0x1fff;
@@ -845,9 +856,12 @@ static struct fw_request *allocate_request(struct fw_card *card,
                return NULL;
        kref_init(&request->kref);
 
+       // NOTE: This can be without irqsave when we can guarantee that __fw_send_request() for
+       // local destination never runs in any type of IRQ context.
+       scoped_guard(spinlock_irqsave, &card->split_timeout.lock)
+               request->response.timestamp = compute_split_timeout_timestamp(card, p->timestamp);
+
        request->response.speed = p->speed;
-       request->response.timestamp =
-                       compute_split_timeout_timestamp(card, p->timestamp);
        request->response.generation = p->generation;
        request->response.ack = 0;
        request->response.callback = free_response_callback;
@@ -1228,16 +1242,17 @@ static const struct fw_address_region registers_region =
          .end   = CSR_REGISTER_BASE | CSR_CONFIG_ROM, };
 
 static void update_split_timeout(struct fw_card *card)
+__must_hold(&card->split_timeout.lock)
 {
        unsigned int cycles;
 
-       cycles = card->split_timeout_hi * 8000 + (card->split_timeout_lo >> 19);
+       cycles = card->split_timeout.hi * 8000 + (card->split_timeout.lo >> 19);
 
        /* minimum per IEEE 1394, maximum which doesn't overflow OHCI */
        cycles = clamp(cycles, 800u, 3u * 8000u);
 
-       card->split_timeout_cycles = cycles;
-       card->split_timeout_jiffies = isoc_cycles_to_jiffies(cycles);
+       card->split_timeout.cycles = cycles;
+       card->split_timeout.jiffies = isoc_cycles_to_jiffies(cycles);
 }
 
 static void handle_registers(struct fw_card *card, struct fw_request *request,
@@ -1287,12 +1302,15 @@ static void handle_registers(struct fw_card *card, struct fw_request *request,
 
        case CSR_SPLIT_TIMEOUT_HI:
                if (tcode == TCODE_READ_QUADLET_REQUEST) {
-                       *data = cpu_to_be32(card->split_timeout_hi);
+                       *data = cpu_to_be32(card->split_timeout.hi);
                } else if (tcode == TCODE_WRITE_QUADLET_REQUEST) {
-                       guard(spinlock_irqsave)(&card->lock);
-
-                       card->split_timeout_hi = be32_to_cpu(*data) & 7;
-                       update_split_timeout(card);
+                       // NOTE: This can be without irqsave when we can guarantee that
+                       // __fw_send_request() for local destination never runs in any type of IRQ
+                       // context.
+                       scoped_guard(spinlock_irqsave, &card->split_timeout.lock) {
+                               card->split_timeout.hi = be32_to_cpu(*data) & 7;
+                               update_split_timeout(card);
+                       }
                } else {
                        rcode = RCODE_TYPE_ERROR;
                }
@@ -1300,12 +1318,15 @@ static void handle_registers(struct fw_card *card, struct fw_request *request,
 
        case CSR_SPLIT_TIMEOUT_LO:
                if (tcode == TCODE_READ_QUADLET_REQUEST) {
-                       *data = cpu_to_be32(card->split_timeout_lo);
+                       *data = cpu_to_be32(card->split_timeout.lo);
                } else if (tcode == TCODE_WRITE_QUADLET_REQUEST) {
-                       guard(spinlock_irqsave)(&card->lock);
-
-                       card->split_timeout_lo = be32_to_cpu(*data) & 0xfff80000;
-                       update_split_timeout(card);
+                       // NOTE: This can be without irqsave when we can guarantee that
+                       // __fw_send_request() for local destination never runs in any type of IRQ
+                       // context.
+                       scoped_guard(spinlock_irqsave, &card->split_timeout.lock) {
+                               card->split_timeout.lo = be32_to_cpu(*data) & 0xfff80000;
+                               update_split_timeout(card);
+                       }
                } else {
                        rcode = RCODE_TYPE_ERROR;
                }

diff --git a/include/linux/firewire.h b/include/linux/firewire.h
index 8d6801c..6d20876 100644 (file)
--- a/include/linux/firewire.h
+++ b/include/linux/firewire.h
@@ -97,18 +97,21 @@ struct fw_card {
                spinlock_t lock;
        } transactions;
 
-       u32 split_timeout_hi;
-       u32 split_timeout_lo;
-       unsigned int split_timeout_cycles;
-       unsigned int split_timeout_jiffies;
+       struct {
+               u32 hi;
+               u32 lo;
+               unsigned int cycles;
+               unsigned int jiffies;
+               spinlock_t lock;
+       } split_timeout;
 
        unsigned long long guid;
        unsigned max_receive;
        int link_speed;
        int config_rom_generation;
 
-       spinlock_t lock; /* Take this lock when handling the lists in
-                         * this struct. */
+       spinlock_t lock;
+
        struct fw_node *local_node;
        struct fw_node *root_node;
        struct fw_node *irm_node;