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Date:   Thu, 30 Apr 2020 17:13:23 -0500
From:   Alex Elder <elder@...aro.org>
To:     davem@...emloft.net
Cc:     evgreen@...omium.org.net, subashab@...eaurora.org,
        cpratapa@...eaurora.org, bjorn.andersson@...aro.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH net-next 2/2] net: ipa: do not cache channel state

It is possible for a GSI channel's state to be changed as a result
of an action by a different execution environment.  Specifically,
the modem is able to issue a GSI generic command that causes a state
change on a GSI channel associated with the AP.

A channel's state only needs to be known when a channel is allocated
or deallocaed, started or stopped, or reset.  So there is little
value in caching the state anyway.

Stop recording a copy of the channel's last known state, and instead
fetch the true state from hardware whenever it's needed.  In such
cases, *do* record the state in a local variable, in case an error
message reports it (so the value reported is the value seen).

Signed-off-by: Alex Elder <elder@...aro.org>
---
 drivers/net/ipa/gsi.c | 87 +++++++++++++++++++++++++++----------------
 drivers/net/ipa/gsi.h |  3 +-
 2 files changed, 55 insertions(+), 35 deletions(-)

diff --git a/drivers/net/ipa/gsi.c b/drivers/net/ipa/gsi.c
index 6946c39b664a..8184d34124b7 100644
--- a/drivers/net/ipa/gsi.c
+++ b/drivers/net/ipa/gsi.c
@@ -415,7 +415,7 @@ static void gsi_evt_ring_de_alloc_command(struct gsi *gsi, u32 evt_ring_id)
 			evt_ring->state);
 }
 
-/* Return the hardware's notion of the current state of a channel */
+/* Fetch the current state of a channel from hardware */
 static enum gsi_channel_state gsi_channel_state(struct gsi_channel *channel)
 {
 	u32 channel_id = gsi_channel_id(channel);
@@ -433,16 +433,18 @@ gsi_channel_command(struct gsi_channel *channel, enum gsi_ch_cmd_opcode opcode)
 {
 	struct completion *completion = &channel->completion;
 	u32 channel_id = gsi_channel_id(channel);
+	struct gsi *gsi = channel->gsi;
 	u32 val;
 
 	val = u32_encode_bits(channel_id, CH_CHID_FMASK);
 	val |= u32_encode_bits(opcode, CH_OPCODE_FMASK);
 
-	if (gsi_command(channel->gsi, GSI_CH_CMD_OFFSET, val, completion))
+	if (gsi_command(gsi, GSI_CH_CMD_OFFSET, val, completion))
 		return 0;	/* Success! */
 
-	dev_err(channel->gsi->dev, "GSI command %u to channel %u timed out "
-		"(state is %u)\n", opcode, channel_id, channel->state);
+	dev_err(gsi->dev,
+		"GSI command %u to channel %u timed out (state is %u)\n",
+		opcode, channel_id, gsi_channel_state(channel));
 
 	return -ETIMEDOUT;
 }
@@ -451,18 +453,21 @@ gsi_channel_command(struct gsi_channel *channel, enum gsi_ch_cmd_opcode opcode)
 static int gsi_channel_alloc_command(struct gsi *gsi, u32 channel_id)
 {
 	struct gsi_channel *channel = &gsi->channel[channel_id];
+	enum gsi_channel_state state;
 	int ret;
 
 	/* Get initial channel state */
-	channel->state = gsi_channel_state(channel);
-
-	if (channel->state != GSI_CHANNEL_STATE_NOT_ALLOCATED)
+	state = gsi_channel_state(channel);
+	if (state != GSI_CHANNEL_STATE_NOT_ALLOCATED)
 		return -EINVAL;
 
 	ret = gsi_channel_command(channel, GSI_CH_ALLOCATE);
-	if (!ret && channel->state != GSI_CHANNEL_STATE_ALLOCATED) {
+
+	/* Channel state will normally have been updated */
+	state = gsi_channel_state(channel);
+	if (!ret && state != GSI_CHANNEL_STATE_ALLOCATED) {
 		dev_err(gsi->dev, "bad channel state (%u) after alloc\n",
-			channel->state);
+			state);
 		ret = -EIO;
 	}
 
@@ -472,18 +477,21 @@ static int gsi_channel_alloc_command(struct gsi *gsi, u32 channel_id)
 /* Start an ALLOCATED channel */
 static int gsi_channel_start_command(struct gsi_channel *channel)
 {
-	enum gsi_channel_state state = channel->state;
+	enum gsi_channel_state state;
 	int ret;
 
+	state = gsi_channel_state(channel);
 	if (state != GSI_CHANNEL_STATE_ALLOCATED &&
 	    state != GSI_CHANNEL_STATE_STOPPED)
 		return -EINVAL;
 
 	ret = gsi_channel_command(channel, GSI_CH_START);
-	if (!ret && channel->state != GSI_CHANNEL_STATE_STARTED) {
+
+	/* Channel state will normally have been updated */
+	state = gsi_channel_state(channel);
+	if (!ret && state != GSI_CHANNEL_STATE_STARTED) {
 		dev_err(channel->gsi->dev,
-			"bad channel state (%u) after start\n",
-			channel->state);
+			"bad channel state (%u) after start\n", state);
 		ret = -EIO;
 	}
 
@@ -493,23 +501,27 @@ static int gsi_channel_start_command(struct gsi_channel *channel)
 /* Stop a GSI channel in STARTED state */
 static int gsi_channel_stop_command(struct gsi_channel *channel)
 {
-	enum gsi_channel_state state = channel->state;
+	enum gsi_channel_state state;
 	int ret;
 
+	state = gsi_channel_state(channel);
 	if (state != GSI_CHANNEL_STATE_STARTED &&
 	    state != GSI_CHANNEL_STATE_STOP_IN_PROC)
 		return -EINVAL;
 
 	ret = gsi_channel_command(channel, GSI_CH_STOP);
-	if (ret || channel->state == GSI_CHANNEL_STATE_STOPPED)
+
+	/* Channel state will normally have been updated */
+	state = gsi_channel_state(channel);
+	if (ret || state == GSI_CHANNEL_STATE_STOPPED)
 		return ret;
 
 	/* We may have to try again if stop is in progress */
-	if (channel->state == GSI_CHANNEL_STATE_STOP_IN_PROC)
+	if (state == GSI_CHANNEL_STATE_STOP_IN_PROC)
 		return -EAGAIN;
 
-	dev_err(channel->gsi->dev, "bad channel state (%u) after stop\n",
-		channel->state);
+	dev_err(channel->gsi->dev,
+		"bad channel state (%u) after stop\n", state);
 
 	return -EIO;
 }
@@ -517,41 +529,49 @@ static int gsi_channel_stop_command(struct gsi_channel *channel)
 /* Reset a GSI channel in ALLOCATED or ERROR state. */
 static void gsi_channel_reset_command(struct gsi_channel *channel)
 {
+	enum gsi_channel_state state;
 	int ret;
 
 	msleep(1);	/* A short delay is required before a RESET command */
 
-	if (channel->state != GSI_CHANNEL_STATE_STOPPED &&
-	    channel->state != GSI_CHANNEL_STATE_ERROR) {
+	state = gsi_channel_state(channel);
+	if (state != GSI_CHANNEL_STATE_STOPPED &&
+	    state != GSI_CHANNEL_STATE_ERROR) {
 		dev_err(channel->gsi->dev,
-			"bad channel state (%u) before reset\n",
-			channel->state);
+			"bad channel state (%u) before reset\n", state);
 		return;
 	}
 
 	ret = gsi_channel_command(channel, GSI_CH_RESET);
-	if (!ret && channel->state != GSI_CHANNEL_STATE_ALLOCATED)
+
+	/* Channel state will normally have been updated */
+	state = gsi_channel_state(channel);
+	if (!ret && state != GSI_CHANNEL_STATE_ALLOCATED)
 		dev_err(channel->gsi->dev,
-			"bad channel state (%u) after reset\n",
-			channel->state);
+			"bad channel state (%u) after reset\n", state);
 }
 
 /* Deallocate an ALLOCATED GSI channel */
 static void gsi_channel_de_alloc_command(struct gsi *gsi, u32 channel_id)
 {
 	struct gsi_channel *channel = &gsi->channel[channel_id];
+	enum gsi_channel_state state;
 	int ret;
 
-	if (channel->state != GSI_CHANNEL_STATE_ALLOCATED) {
-		dev_err(gsi->dev, "bad channel state (%u) before dealloc\n",
-			channel->state);
+	state = gsi_channel_state(channel);
+	if (state != GSI_CHANNEL_STATE_ALLOCATED) {
+		dev_err(gsi->dev,
+			"bad channel state (%u) before dealloc\n", state);
 		return;
 	}
 
 	ret = gsi_channel_command(channel, GSI_CH_DE_ALLOC);
-	if (!ret && channel->state != GSI_CHANNEL_STATE_NOT_ALLOCATED)
-		dev_err(gsi->dev, "bad channel state (%u) after dealloc\n",
-			channel->state);
+
+	/* Channel state will normally have been updated */
+	state = gsi_channel_state(channel);
+	if (!ret && state != GSI_CHANNEL_STATE_NOT_ALLOCATED)
+		dev_err(gsi->dev,
+			"bad channel state (%u) after dealloc\n", state);
 }
 
 /* Ring an event ring doorbell, reporting the last entry processed by the AP.
@@ -778,6 +798,7 @@ int gsi_channel_start(struct gsi *gsi, u32 channel_id)
 int gsi_channel_stop(struct gsi *gsi, u32 channel_id)
 {
 	struct gsi_channel *channel = &gsi->channel[channel_id];
+	enum gsi_channel_state state;
 	u32 retries;
 	int ret;
 
@@ -787,7 +808,8 @@ int gsi_channel_stop(struct gsi *gsi, u32 channel_id)
 	 * STOP command timed out.  We won't stop a channel if stopping it
 	 * was successful previously (so we still want the freeze above).
 	 */
-	if (channel->state == GSI_CHANNEL_STATE_STOPPED)
+	state = gsi_channel_state(channel);
+	if (state == GSI_CHANNEL_STATE_STOPPED)
 		return 0;
 
 	/* RX channels might require a little time to enter STOPPED state */
@@ -941,7 +963,6 @@ static void gsi_isr_chan_ctrl(struct gsi *gsi)
 		channel_mask ^= BIT(channel_id);
 
 		channel = &gsi->channel[channel_id];
-		channel->state = gsi_channel_state(channel);
 
 		complete(&channel->completion);
 	}
diff --git a/drivers/net/ipa/gsi.h b/drivers/net/ipa/gsi.h
index 0698ff1ae7a6..19471017fadf 100644
--- a/drivers/net/ipa/gsi.h
+++ b/drivers/net/ipa/gsi.h
@@ -113,8 +113,7 @@ struct gsi_channel {
 	u16 tre_count;
 	u16 event_count;
 
-	struct completion completion;	/* signals channel state changes */
-	enum gsi_channel_state state;
+	struct completion completion;	/* signals channel command completion */
 
 	struct gsi_ring tre_ring;
 	u32 evt_ring_id;
-- 
2.20.1

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