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>

1 files changed, 22 insertions, 9 deletions

diff --git a/drivers/net/ethernet/sfc/efx.c b/drivers/net/ethernet/sfc/efx.c
index de162474c3c5..9d4ab5e5e1fa 100644
--- a/drivers/net/ethernet/sfc/efx.c
+++ b/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);
 }
 
 /**************************************************************************