sfc: Correct interrupt timer quantum for Siena (normal and turbo mode)

We currently assume that the timer quantum for Siena is 5 us, the same
as for Falcon.  This is not correct; timer ticks are generated on a
rota which takes a minimum of 768 cycles (each event delivery or other
timer change will delay it by 3 cycles).  The timer quantum should be
6.144 or 3.072 us depending on whether turbo mode is active.

Replace EFX_IRQ_MOD_RESOLUTION with a timer_quantum_ns field in struct
efx_nic, initialised by the efx_nic_type::probe function.

While we're at it, replace EFX_IRQ_MOD_MAX with a timer_period_max
field in struct efx_nic_type.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

drivers/net/ethernet/sfc/efx.c

@@ -1513,13 +1513,13 @@ static void efx_remove_all(struct efx_nic *efx)
  *
  **************************************************************************/
 
-static unsigned int irq_mod_ticks(unsigned int usecs, unsigned int resolution)
+static unsigned int irq_mod_ticks(unsigned int usecs, unsigned int quantum_ns)
 {
 	if (usecs == 0)
 		return 0;
-	if (usecs < resolution)
+	if (usecs * 1000 < quantum_ns)
 		return 1; /* never round down to 0 */
-	return usecs / resolution;
+	return usecs * 1000 / quantum_ns;
 }
 
 /* Set interrupt moderation parameters */
@@ -1528,14 +1528,20 @@ int efx_init_irq_moderation(struct efx_nic *efx, unsigned int tx_usecs,
 			    bool rx_may_override_tx)
 {
 	struct efx_channel *channel;
-	unsigned tx_ticks = irq_mod_ticks(tx_usecs, EFX_IRQ_MOD_RESOLUTION);
-	unsigned rx_ticks = irq_mod_ticks(rx_usecs, EFX_IRQ_MOD_RESOLUTION);
+	unsigned int irq_mod_max = DIV_ROUND_UP(efx->type->timer_period_max *
+						efx->timer_quantum_ns,
+						1000);
+	unsigned int tx_ticks;
+	unsigned int rx_ticks;
 
 	EFX_ASSERT_RESET_SERIALISED(efx);
 
-	if (tx_ticks > EFX_IRQ_MOD_MAX || rx_ticks > EFX_IRQ_MOD_MAX)
+	if (tx_usecs > irq_mod_max || rx_usecs > irq_mod_max)
 		return -EINVAL;
 
+	tx_ticks = irq_mod_ticks(tx_usecs, efx->timer_quantum_ns);
+	rx_ticks = irq_mod_ticks(rx_usecs, efx->timer_quantum_ns);
+
 	if (tx_ticks != rx_ticks && efx->tx_channel_offset == 0 &&
 	    !rx_may_override_tx) {
 		netif_err(efx, drv, efx->net_dev, "Channels are shared. "
@@ -1558,8 +1564,14 @@ int efx_init_irq_moderation(struct efx_nic *efx, unsigned int tx_usecs,
 void efx_get_irq_moderation(struct efx_nic *efx, unsigned int *tx_usecs,
 			    unsigned int *rx_usecs, bool *rx_adaptive)
 {
+	/* We must round up when converting ticks to microseconds
+	 * because we round down when converting the other way.
+	 */
+
 	*rx_adaptive = efx->irq_rx_adaptive;
-	*rx_usecs = efx->irq_rx_moderation * EFX_IRQ_MOD_RESOLUTION;
+	*rx_usecs = DIV_ROUND_UP(efx->irq_rx_moderation *
+				 efx->timer_quantum_ns,
+				 1000);
 
 	/* If channels are shared between RX and TX, so is IRQ
 	 * moderation.  Otherwise, IRQ moderation is the same for all
@@ -1568,9 +1580,10 @@ void efx_get_irq_moderation(struct efx_nic *efx, unsigned int *tx_usecs,
 	if (efx->tx_channel_offset == 0)
 		*tx_usecs = *rx_usecs;
 	else
-		*tx_usecs =
+		*tx_usecs = DIV_ROUND_UP(
 			efx->channel[efx->tx_channel_offset]->irq_moderation *
-			EFX_IRQ_MOD_RESOLUTION;
+			efx->timer_quantum_ns,
+			1000);
 }
 
 /**************************************************************************

drivers/net/ethernet/sfc/falcon.c

@@ -103,8 +103,6 @@ static void falcon_push_irq_moderation(struct efx_channel *channel)
 	efx_dword_t timer_cmd;
 	struct efx_nic *efx = channel->efx;
 
-	BUILD_BUG_ON(EFX_IRQ_MOD_MAX > (1 << FRF_AB_TC_TIMER_VAL_WIDTH));
-
 	/* Set timer register */
 	if (channel->irq_moderation) {
 		EFX_POPULATE_DWORD_2(timer_cmd,
@@ -1471,6 +1469,8 @@ static int falcon_probe_nic(struct efx_nic *efx)
 		goto fail5;
 	}
 
+	efx->timer_quantum_ns = 4968; /* 621 cycles */
+
 	/* Initialise I2C adapter */
 	board = falcon_board(efx);
 	board->i2c_adap.owner = THIS_MODULE;
@@ -1785,6 +1785,7 @@ const struct efx_nic_type falcon_a1_nic_type = {
 	.rx_buffer_padding = 0x24,
 	.max_interrupt_mode = EFX_INT_MODE_MSI,
 	.phys_addr_channels = 4,
+	.timer_period_max =  1 << FRF_AB_TC_TIMER_VAL_WIDTH,
 	.tx_dc_base = 0x130000,
 	.rx_dc_base = 0x100000,
 	.offload_features = NETIF_F_IP_CSUM,
@@ -1836,6 +1837,7 @@ const struct efx_nic_type falcon_b0_nic_type = {
 	.phys_addr_channels = 32, /* Hardware limit is 64, but the legacy
 				   * interrupt handler only supports 32
 				   * channels */
+	.timer_period_max =  1 << FRF_AB_TC_TIMER_VAL_WIDTH,
 	.tx_dc_base = 0x130000,
 	.rx_dc_base = 0x100000,
 	.offload_features = NETIF_F_IP_CSUM | NETIF_F_RXHASH | NETIF_F_NTUPLE,

drivers/net/ethernet/sfc/net_driver.h

@@ -624,6 +624,7 @@ struct efx_filter_state;
  * @membase_phys: Memory BAR value as physical address
  * @membase: Memory BAR value
  * @interrupt_mode: Interrupt mode
+ * @timer_quantum_ns: Interrupt timer quantum, in nanoseconds
  * @irq_rx_adaptive: Adaptive IRQ moderation enabled for RX event queues
  * @irq_rx_moderation: IRQ moderation time for RX event queues
  * @msg_enable: Log message enable flags
@@ -706,6 +707,7 @@ struct efx_nic {
 	void __iomem *membase;
 
 	enum efx_int_mode interrupt_mode;
+	unsigned int timer_quantum_ns;
 	bool irq_rx_adaptive;
 	unsigned int irq_rx_moderation;
 	u32 msg_enable;
@@ -845,6 +847,7 @@ static inline unsigned int efx_port_num(struct efx_nic *efx)
  *	from &enum efx_init_mode.
  * @phys_addr_channels: Number of channels with physically addressed
  *	descriptors
+ * @timer_period_max: Maximum period of interrupt timer (in ticks)
  * @tx_dc_base: Base address in SRAM of TX queue descriptor caches
  * @rx_dc_base: Base address in SRAM of RX queue descriptor caches
  * @offload_features: net_device feature flags for protocol offload
@@ -889,6 +892,7 @@ struct efx_nic_type {
 	unsigned int rx_buffer_padding;
 	unsigned int max_interrupt_mode;
 	unsigned int phys_addr_channels;
+	unsigned int timer_period_max;
 	unsigned int tx_dc_base;
 	unsigned int rx_dc_base;
 	netdev_features_t offload_features;

drivers/net/ethernet/sfc/nic.h

@@ -205,9 +205,6 @@ extern irqreturn_t efx_nic_fatal_interrupt(struct efx_nic *efx);
 extern irqreturn_t falcon_legacy_interrupt_a1(int irq, void *dev_id);
 extern void falcon_irq_ack_a1(struct efx_nic *efx);
 
-#define EFX_IRQ_MOD_RESOLUTION	5
-#define EFX_IRQ_MOD_MAX		0x1000
-
 /* Global Resources */
 extern int efx_nic_flush_queues(struct efx_nic *efx);
 extern void falcon_start_nic_stats(struct efx_nic *efx);

drivers/net/ethernet/sfc/siena.c

@@ -35,8 +35,6 @@ static void siena_push_irq_moderation(struct efx_channel *channel)
 {
 	efx_dword_t timer_cmd;
 
-	BUILD_BUG_ON(EFX_IRQ_MOD_MAX > (1 << FRF_CZ_TC_TIMER_VAL_WIDTH));
-
 	if (channel->irq_moderation)
 		EFX_POPULATE_DWORD_2(timer_cmd,
 				     FRF_CZ_TC_TIMER_MODE,
@@ -216,7 +214,15 @@ static int siena_reset_hw(struct efx_nic *efx, enum reset_type method)
 
 static int siena_probe_nvconfig(struct efx_nic *efx)
 {
-	return efx_mcdi_get_board_cfg(efx, efx->net_dev->perm_addr, NULL, NULL);
+	u32 caps = 0;
+	int rc;
+
+	rc = efx_mcdi_get_board_cfg(efx, efx->net_dev->perm_addr, NULL, &caps);
+
+	efx->timer_quantum_ns =
+		(caps & (1 << MC_CMD_CAPABILITIES_TURBO_ACTIVE_LBN)) ?
+		3072 : 6144; /* 768 cycles */
+	return rc;
 }
 
 static int siena_probe_nic(struct efx_nic *efx)
@@ -644,6 +650,7 @@ const struct efx_nic_type siena_a0_nic_type = {
 	.phys_addr_channels = 32, /* Hardware limit is 64, but the legacy
 				   * interrupt handler only supports 32
 				   * channels */
+	.timer_period_max = 1 << FRF_CZ_TC_TIMER_VAL_WIDTH,
 	.tx_dc_base = 0x88000,
 	.rx_dc_base = 0x68000,
 	.offload_features = (NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM |