firewire: core: integrate software-forced bus resets with bus management

Bus resets which are triggered
  - by the kernel drivers after updates of the local nodes' config ROM,
  - by userspace software via ioctl
shall be deferred until after >=2 seconds after the last bus reset.

If multiple modifications of the local nodes' config ROM happen in a row,
only a single bus reset should happen after them.

When the local node's link goes from inactive to active or vice versa,
and at the two occasions of bus resets mentioned above --- and if the
current gap count differs from 63 --- the bus reset should be preceded
by a PHY configuration packet that reaffirms the gap count.  Otherwise a
bus manager would have to reset the bus again right after that.

This is necessary to promote bus stability, e.g. leave grace periods for
allocations and reallocations of isochronous channels and bandwidth,
SBP-2 reconnections etc.; see IEEE 1394 clause 8.2.1.

This change implements all of the above by moving bus reset initiation
into a delayed work (except for bus resets which are triggered by the
bus manager workqueue job and are performed there immediately).  It
comes with a necessary addition to the card driver methods that allows
to get the current gap count from PHY registers.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

1 files changed, 52 insertions, 16 deletions

diff --git a/drivers/firewire/core-card.c b/drivers/firewire/core-card.c
index 6c316cf..2bb5c03 100644
--- a/drivers/firewire/core-card.c
+++ b/drivers/firewire/core-card.c
@@ -204,6 +204,45 @@ void fw_core_remove_descriptor(struct fw_descriptor *desc)
 }
 EXPORT_SYMBOL(fw_core_remove_descriptor);
 
+static int reset_bus(struct fw_card *card, bool short_reset)
+{
+	int reg = short_reset ? 5 : 1;
+	int bit = short_reset ? PHY_BUS_SHORT_RESET : PHY_BUS_RESET;
+
+	return card->driver->update_phy_reg(card, reg, 0, bit);
+}
+
+void fw_schedule_bus_reset(struct fw_card *card, bool delayed, bool short_reset)
+{
+	/* We don't try hard to sort out requests of long vs. short resets. */
+	card->br_short = short_reset;
+
+	/* Use an arbitrary short delay to combine multiple reset requests. */
+	fw_card_get(card);
+	if (!schedule_delayed_work(&card->br_work,
+				   delayed ? DIV_ROUND_UP(HZ, 100) : 0))
+		fw_card_put(card);
+}
+EXPORT_SYMBOL(fw_schedule_bus_reset);
+
+static void br_work(struct work_struct *work)
+{
+	struct fw_card *card = container_of(work, struct fw_card, br_work.work);
+
+	/* Delay for 2s after last reset per IEEE 1394 clause 8.2.1. */
+	if (card->reset_jiffies != 0 &&
+	    time_is_after_jiffies(card->reset_jiffies + 2 * HZ)) {
+		if (!schedule_delayed_work(&card->br_work, 2 * HZ))
+			fw_card_put(card);
+		return;
+	}
+
+	fw_send_phy_config(card, FW_PHY_CONFIG_NO_NODE_ID, card->generation,
+			   FW_PHY_CONFIG_CURRENT_GAP_COUNT);
+	reset_bus(card, card->br_short);
+	fw_card_put(card);
+}
+
 static void allocate_broadcast_channel(struct fw_card *card, int generation)
 {
 	int channel, bandwidth = 0;
@@ -230,13 +269,13 @@ static const char gap_count_table[] = {
 void fw_schedule_bm_work(struct fw_card *card, unsigned long delay)
 {
 	fw_card_get(card);
-	if (!schedule_delayed_work(&card->work, delay))
+	if (!schedule_delayed_work(&card->bm_work, delay))
 		fw_card_put(card);
 }
 
-static void fw_card_bm_work(struct work_struct *work)
+static void bm_work(struct work_struct *work)
 {
-	struct fw_card *card = container_of(work, struct fw_card, work.work);
+	struct fw_card *card = container_of(work, struct fw_card, bm_work.work);
 	struct fw_device *root_device;
 	struct fw_node *root_node;
 	int root_id, new_root_id, irm_id, bm_id, local_id;
@@ -413,7 +452,7 @@ static void fw_card_bm_work(struct work_struct *work)
 		fw_notify("phy config: card %d, new root=%x, gap_count=%d\n",
 			  card->index, new_root_id, gap_count);
 		fw_send_phy_config(card, new_root_id, generation, gap_count);
-		fw_core_initiate_bus_reset(card, 1);
+		reset_bus(card, true);
 		/* Will allocate broadcast channel after the reset. */
 		goto out;
 	}
@@ -465,7 +504,8 @@ void fw_card_initialize(struct fw_card *card,
 
 	card->local_node = NULL;
 
-	INIT_DELAYED_WORK(&card->work, fw_card_bm_work);
+	INIT_DELAYED_WORK(&card->br_work, br_work);
+	INIT_DELAYED_WORK(&card->bm_work, bm_work);
 }
 EXPORT_SYMBOL(fw_card_initialize);
 
@@ -491,7 +531,6 @@ int fw_card_add(struct fw_card *card,
 }
 EXPORT_SYMBOL(fw_card_add);
 
-
 /*
  * The next few functions implement a dummy driver that is used once a card
  * driver shuts down an fw_card.  This allows the driver to cleanly unload,
@@ -507,6 +546,11 @@ static int dummy_enable(struct fw_card *card,
 	return -1;
 }
 
+static int dummy_read_phy_reg(struct fw_card *card, int address)
+{
+	return -ENODEV;
+}
+
 static int dummy_update_phy_reg(struct fw_card *card, int address,
 				int clear_bits, int set_bits)
 {
@@ -547,6 +591,7 @@ static int dummy_enable_phys_dma(struct fw_card *card,
 
 static const struct fw_card_driver dummy_driver_template = {
 	.enable          = dummy_enable,
+	.read_phy_reg    = dummy_read_phy_reg,
 	.update_phy_reg  = dummy_update_phy_reg,
 	.set_config_rom  = dummy_set_config_rom,
 	.send_request    = dummy_send_request,
@@ -568,7 +613,7 @@ void fw_core_remove_card(struct fw_card *card)
 
 	card->driver->update_phy_reg(card, 4,
 				     PHY_LINK_ACTIVE | PHY_CONTENDER, 0);
-	fw_core_initiate_bus_reset(card, 1);
+	fw_schedule_bus_reset(card, false, true);
 
 	mutex_lock(&card_mutex);
 	list_del_init(&card->link);
@@ -588,12 +633,3 @@ void fw_core_remove_card(struct fw_card *card)
 	WARN_ON(!list_empty(&card->transaction_list));
 }
 EXPORT_SYMBOL(fw_core_remove_card);
-
-int fw_core_initiate_bus_reset(struct fw_card *card, int short_reset)
-{
-	int reg = short_reset ? 5 : 1;
-	int bit = short_reset ? PHY_BUS_SHORT_RESET : PHY_BUS_RESET;
-
-	return card->driver->update_phy_reg(card, reg, 0, bit);
-}
-EXPORT_SYMBOL(fw_core_initiate_bus_reset);