sfc: Extend the legacy interrupt workarounds

Siena has two problems with legacy interrupts:
  1. There is no synchronisation between the ISR read completion,
     and the interrupt deassert message.
  2. A downstream read at the "wrong" moment can return 0, and
     suppress generating the next interrupt.

Falcon should suffer from both of these, and it appears it does.
Enable EFX_WORKAROUND_15783 on Falcon as well.

Also, when we see queues == 0, ensure we always schedule or rearm
every event queue.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 10 insertions, 15 deletions

diff --git a/drivers/net/sfc/nic.c b/drivers/net/sfc/nic.c
index 23738f80835b..b61674cb0c19 100644
--- a/drivers/net/sfc/nic.c
+++ b/drivers/net/sfc/nic.c
@@ -1356,33 +1356,28 @@ static irqreturn_t efx_legacy_interrupt(int irq, void *dev_id)
                 }
                 result = IRQ_HANDLED;
 
-        } else if (EFX_WORKAROUND_15783(efx) &&
-                   efx->irq_zero_count++ == 0) {
+        } else if (EFX_WORKAROUND_15783(efx)) {
                 efx_qword_t *event;
 
-                /* Ensure we rearm all event queues */
+                /* We can't return IRQ_HANDLED more than once on seeing ISR=0
+                 * because this might be a shared interrupt. */
+                if (efx->irq_zero_count++ == 0)
+                        result = IRQ_HANDLED;
+
+                /* Ensure we schedule or rearm all event queues */
                 efx_for_each_channel(channel, efx) {
                         event = efx_event(channel, channel->eventq_read_ptr);
                         if (efx_event_present(event))
                                 efx_schedule_channel(channel);
+                        else
+                                efx_nic_eventq_read_ack(channel);
                 }
-
-                result = IRQ_HANDLED;
         }
 
         if (result == IRQ_HANDLED) {
                 efx->last_irq_cpu = raw_smp_processor_id();
                 EFX_TRACE(efx, "IRQ %d on CPU %d status " EFX_DWORD_FMT "\n",
                           irq, raw_smp_processor_id(), EFX_DWORD_VAL(reg));
-        } else if (EFX_WORKAROUND_15783(efx)) {
-                /* We can't return IRQ_HANDLED more than once on seeing ISR0=0
-                 * because this might be a shared interrupt, but we do need to
-                 * check the channel every time and preemptively rearm it if
-                 * it's idle. */
-                efx_for_each_channel(channel, efx) {
-                        if (!channel->work_pending)
-                                efx_nic_eventq_read_ack(channel);
-                }
         }
 
         return result;
diff --git a/drivers/net/sfc/workarounds.h b/drivers/net/sfc/workarounds.h
index acd9c734e483..518f7fc91473 100644
--- a/drivers/net/sfc/workarounds.h
+++ b/drivers/net/sfc/workarounds.h
@@ -37,7 +37,7 @@
 /* Truncated IPv4 packets can confuse the TX packet parser */
 #define EFX_WORKAROUND_15592 EFX_WORKAROUND_FALCON_AB
 /* Legacy ISR read can return zero once */
-#define EFX_WORKAROUND_15783 EFX_WORKAROUND_SIENA
+#define EFX_WORKAROUND_15783 EFX_WORKAROUND_ALWAYS
 /* Legacy interrupt storm when interrupt fifo fills */
 #define EFX_WORKAROUND_17213 EFX_WORKAROUND_SIENA