Merge branch 'net-ipa-don-t-disable-napi-in-suspend'

Alex Elder says:

====================
net: ipa: don't disable NAPI in suspend

This is version 2 of a series that reworks the order in which things
happen during channel stop and suspend (and start and resume), in
order to address a hang that has been observed during suspend.
The introductory message on the first version of the series gave
some history which is omitted here.

The end result of this series is that we only enable NAPI and the
I/O completion interrupt on a channel when we start the channel for
the first time.  And we only disable them when stopping the channel
"for good."  In other words, NAPI and the completion interrupt
remain enabled while a channel is stopped for suspend.

One comment on version 1 of the series suggested *not* returning
early on success in a function, instead having both success and
error paths return from the same point at the end of the function
block.  This has been addressed in this version.

In addition, this version consolidates things a little bit, but the
net result of the series is exactly the same as version 1 (with the
exception of the return fix mentioned above).

First, patch 6 in the first version was a small step to make patch 7
easier to understand.  The two have been combined now.

Second, previous version moved (and for suspend/resume, eliminated)
I/O completion interrupt and NAPI disable/enable control in separate
steps (patches).  Now both are moved around together in patch 5 and
6, which eliminates the need for the final (NAPI-only) patch.

I won't repeat the patch summaries provided in v1:
  https://lore.kernel.org/netdev/20210129202019.2099259-1-elder@linaro.org/

Many thanks to Willem de Bruijn for his thoughtful input.
====================

Link: https://lore.kernel.org/r/20210201172850.2221624-1-elder@linaro.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ipa/gsi.c

@@ -725,22 +725,38 @@ static void gsi_evt_ring_program(struct gsi *gsi, u32 evt_ring_id)
 	gsi_evt_ring_doorbell(gsi, evt_ring_id, 0);
 }
 
-/* Return the last (most recent) transaction completed on a channel. */
+/* Find the transaction whose completion indicates a channel is quiesced */
 static struct gsi_trans *gsi_channel_trans_last(struct gsi_channel *channel)
 {
 	struct gsi_trans_info *trans_info = &channel->trans_info;
+	const struct list_head *list;
 	struct gsi_trans *trans;
 
 	spin_lock_bh(&trans_info->spinlock);
 
-	if (!list_empty(&trans_info->complete))
-		trans = list_last_entry(&trans_info->complete,
-					struct gsi_trans, links);
-	else if (!list_empty(&trans_info->polled))
-		trans = list_last_entry(&trans_info->polled,
-					struct gsi_trans, links);
-	else
-		trans = NULL;
+	/* There is a small chance a TX transaction got allocated just
+	 * before we disabled transmits, so check for that.
+	 */
+	if (channel->toward_ipa) {
+		list = &trans_info->alloc;
+		if (!list_empty(list))
+			goto done;
+		list = &trans_info->pending;
+		if (!list_empty(list))
+			goto done;
+	}
+
+	/* Otherwise (TX or RX) we want to wait for anything that
+	 * has completed, or has been polled but not released yet.
+	 */
+	list = &trans_info->complete;
+	if (!list_empty(list))
+		goto done;
+	list = &trans_info->polled;
+	if (list_empty(list))
+		list = NULL;
+done:
+	trans = list ? list_last_entry(list, struct gsi_trans, links) : NULL;
 
 	/* Caller will wait for this, so take a reference */
 	if (trans)
@@ -764,24 +780,6 @@ static void gsi_channel_trans_quiesce(struct gsi_channel *channel)
 	}
 }
 
-/* Stop channel activity.  Transactions may not be allocated until thawed. */
-static void gsi_channel_freeze(struct gsi_channel *channel)
-{
-	gsi_channel_trans_quiesce(channel);
-
-	napi_disable(&channel->napi);
-
-	gsi_irq_ieob_disable_one(channel->gsi, channel->evt_ring_id);
-}
-
-/* Allow transactions to be used on the channel again. */
-static void gsi_channel_thaw(struct gsi_channel *channel)
-{
-	gsi_irq_ieob_enable_one(channel->gsi, channel->evt_ring_id);
-
-	napi_enable(&channel->napi);
-}
-
 /* Program a channel for use */
 static void gsi_channel_program(struct gsi_channel *channel, bool doorbell)
 {
@@ -873,31 +871,47 @@ static void gsi_channel_deprogram(struct gsi_channel *channel)
 	/* Nothing to do */
 }
 
-/* Start an allocated GSI channel */
-int gsi_channel_start(struct gsi *gsi, u32 channel_id)
+static int __gsi_channel_start(struct gsi_channel *channel, bool start)
 {
-	struct gsi_channel *channel = &gsi->channel[channel_id];
+	struct gsi *gsi = channel->gsi;
 	int ret;
 
+	if (!start)
+		return 0;
+
 	mutex_lock(&gsi->mutex);
 
 	ret = gsi_channel_start_command(channel);
 
 	mutex_unlock(&gsi->mutex);
 
-	gsi_channel_thaw(channel);
-
 	return ret;
 }
 
-/* Stop a started channel */
-int gsi_channel_stop(struct gsi *gsi, u32 channel_id)
+/* Start an allocated GSI channel */
+int gsi_channel_start(struct gsi *gsi, u32 channel_id)
 {
 	struct gsi_channel *channel = &gsi->channel[channel_id];
-	u32 retries = GSI_CHANNEL_STOP_RETRIES;
 	int ret;
 
-	gsi_channel_freeze(channel);
+	/* Enable NAPI and the completion interrupt */
+	napi_enable(&channel->napi);
+	gsi_irq_ieob_enable_one(gsi, channel->evt_ring_id);
+
+	ret = __gsi_channel_start(channel, true);
+	if (ret) {
+		gsi_irq_ieob_disable_one(gsi, channel->evt_ring_id);
+		napi_disable(&channel->napi);
+	}
+
+	return ret;
+}
+
+static int gsi_channel_stop_retry(struct gsi_channel *channel)
+{
+	u32 retries = GSI_CHANNEL_STOP_RETRIES;
+	struct gsi *gsi = channel->gsi;
+	int ret;
 
 	mutex_lock(&gsi->mutex);
 
@@ -910,11 +924,39 @@ int gsi_channel_stop(struct gsi *gsi, u32 channel_id)
 
 	mutex_unlock(&gsi->mutex);
 
-	/* Thaw the channel if we need to retry (or on error) */
-	if (ret)
-		gsi_channel_thaw(channel);
+	return ret;
+}
+
+static int __gsi_channel_stop(struct gsi_channel *channel, bool stop)
+{
+	int ret;
+
+	/* Wait for any underway transactions to complete before stopping. */
+	gsi_channel_trans_quiesce(channel);
+
+	ret = stop ? gsi_channel_stop_retry(channel) : 0;
+	/* Finally, ensure NAPI polling has finished. */
+	if (!ret)
+		napi_synchronize(&channel->napi);
+
+	return ret;
+}
 
+/* Stop a started channel */
+int gsi_channel_stop(struct gsi *gsi, u32 channel_id)
+{
+	struct gsi_channel *channel = &gsi->channel[channel_id];
+	int ret;
+
+	/* Only disable the completion interrupt if stop is successful */
+	ret = __gsi_channel_stop(channel, true);
+	if (ret)
 		return ret;
+
+	gsi_irq_ieob_disable_one(gsi, channel->evt_ring_id);
+	napi_disable(&channel->napi);
+
+	return 0;
 }
 
 /* Reset and reconfigure a channel, (possibly) enabling the doorbell engine */
@@ -940,12 +982,7 @@ int gsi_channel_suspend(struct gsi *gsi, u32 channel_id, bool stop)
 {
 	struct gsi_channel *channel = &gsi->channel[channel_id];
 
-	if (stop)
-		return gsi_channel_stop(gsi, channel_id);
-
-	gsi_channel_freeze(channel);
-
-	return 0;
+	return __gsi_channel_stop(channel, stop);
 }
 
 /* Resume a suspended channel (starting will be requested if STOPPED) */
@@ -953,12 +990,7 @@ int gsi_channel_resume(struct gsi *gsi, u32 channel_id, bool start)
 {
 	struct gsi_channel *channel = &gsi->channel[channel_id];
 
-	if (start)
-		return gsi_channel_start(gsi, channel_id);
-
-	gsi_channel_thaw(channel);
-
-	return 0;
+	return __gsi_channel_start(channel, start);
 }
 
 /**