netdev - [PATCH net 2/2] net: ipa: re-enable NAPI before enabling interrupt

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Date:   Thu,  7 Jan 2021 15:43:25 -0600
From:   Alex Elder <elder@...aro.org>
To:     davem@...emloft.net, kuba@...nel.org
Cc:     evgreen@...omium.org, bjorn.andersson@...aro.org,
        cpratapa@...eaurora.org, subashab@...eaurora.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH net 2/2] net: ipa: re-enable NAPI before enabling interrupt

When we stop or suspend a channel, we first "freeze" it.  The last
part of that involves disabling NAPI, and disabling the IEOB
interrupt that schedules NAPI when it occurs.  On resume, a "thaw"
does the inverse of these activities, in reverse order.  Currently
these are ordered such that NAPI is disabled before interrupts on
suspend, and NAPI is re-enabled after interrupts on resume.

An interrupt occurring while NAPI is disabled will request a NAPI
schedule, but polling is deferred until after NAPI is enabled again.
When NAPI is re-enabled, polling is allowed again, but enabling
NAPI does not schedule a poll (i.e., it won't trigger polling to
handle a schedule request that occurred while disabled).  Polling
won't commence until the next napi_schedule() request occurs.

Instead, disable completion interrupts *before* disabling NAPI when
stopping a channel, and re-enable interrupts *after* re-enabling
NAPI.  That way NAPI is always enabled when an interrupt occurs,
and polling to handle the interrupt can commence immediately.

The channel STOPPING flag ensures the polling function won't
re-enable the completion interrupt while we are stopping.

Fixes: 650d1603825d8 ("soc: qcom: ipa: the generic software interface")
Signed-off-by: Alex Elder <elder@...aro.org>
---
 drivers/net/ipa/gsi.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ipa/gsi.c b/drivers/net/ipa/gsi.c
index 7e7629902911e..9bde6d02b1cd6 100644
--- a/drivers/net/ipa/gsi.c
+++ b/drivers/net/ipa/gsi.c
@@ -743,21 +743,21 @@ static void gsi_channel_freeze(struct gsi_channel *channel)
 	set_bit(GSI_CHANNEL_FLAG_STOPPING, channel->flags);
 	smp_mb__after_atomic();	/* Ensure gsi_channel_poll() sees new value */

-	napi_disable(&channel->napi);
-
 	gsi_irq_ieob_disable(channel->gsi, channel->evt_ring_id);
+
+	napi_disable(&channel->napi);
 }

 /* Allow transactions to be used on the channel again. */
 static void gsi_channel_thaw(struct gsi_channel *channel)
 {
-	gsi_irq_ieob_enable(channel->gsi, channel->evt_ring_id);
-
 	/* Allow the NAPI poll loop to re-enable interrupts again */
 	clear_bit(GSI_CHANNEL_FLAG_STOPPING, channel->flags);
 	smp_mb__after_atomic();	/* Ensure gsi_channel_poll() sees new value */

 	napi_enable(&channel->napi);
+
+	gsi_irq_ieob_enable(channel->gsi, channel->evt_ring_id);
 }

 /* Program a channel for use */
-- 
2.20.1