net: ipa: introduce channel flow control

One quirk for certain versions of IPA is that endpoint DELAY mode
does not work properly.  IPA DELAY mode prevents any packets from
being delivered to the IPA core for processing on a TX endpoint.
The AP uses DELAY mode when the modem crashes, to prevent modem TX
endpoints from generating traffic during crash recovery.  Without
this, there is a chance the hardware will stall during recovery from
a modem crash.

To achieve a similar effect, a GSI FLOW_CONTROLLED channel state
was created.  A STARTED TX channel can be placed in FLOW_CONTROLLED
state, which prevents the transfer of any more packets.  A channel
in FLOW_CONTROLLED state can be either returned to STARTED state, or
can be transitioned to STOPPED state.

Because this operates on GSI channels, two generic commands were
added to allow the AP to control this state for modem channels
(similar to the ALLOCATE and HALT channel commands).

Previously the code assumed this quirk only applied to IPA v4.2.
In fact, channel flow control (rather than endpoint DELAY mode)
should be used for all versions *starting* with IPA v4.2.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 30 insertions, 20 deletions

diff --git a/drivers/net/ipa/ipa_endpoint.c b/drivers/net/ipa/ipa_endpoint.c
index fba576a7717f..b475f89e09bd 100644
--- a/drivers/net/ipa/ipa_endpoint.c
+++ b/drivers/net/ipa/ipa_endpoint.c
@@ -237,7 +237,8 @@ static struct gsi_trans *ipa_endpoint_trans_alloc(struct ipa_endpoint *endpoint,
 }
 
 /* suspend_delay represents suspend for RX, delay for TX endpoints.
- * Note that suspend is not supported starting with IPA v4.0.
+ * Note that suspend is not supported starting with IPA v4.0, and
+ * delay mode should not be used starting with IPA v4.2.
  */
 static bool
 ipa_endpoint_init_ctrl(struct ipa_endpoint *endpoint, bool suspend_delay)
@@ -248,11 +249,8 @@ ipa_endpoint_init_ctrl(struct ipa_endpoint *endpoint, bool suspend_delay)
 	u32 mask;
 	u32 val;
 
-	/* Suspend is not supported for IPA v4.0+.  Delay doesn't work
-	 * correctly on IPA v4.2.
-	 */
 	if (endpoint->toward_ipa)
-		WARN_ON(ipa->version == IPA_VERSION_4_2);
+		WARN_ON(ipa->version >= IPA_VERSION_4_2);
 	else
 		WARN_ON(ipa->version >= IPA_VERSION_4_0);
 
@@ -270,15 +268,15 @@ ipa_endpoint_init_ctrl(struct ipa_endpoint *endpoint, bool suspend_delay)
 	return state;
 }
 
-/* We currently don't care what the previous state was for delay mode */
+/* We don't care what the previous state was for delay mode */
 static void
 ipa_endpoint_program_delay(struct ipa_endpoint *endpoint, bool enable)
 {
+	/* Delay mode should not be used for IPA v4.2+ */
+	WARN_ON(endpoint->ipa->version >= IPA_VERSION_4_2);
 	WARN_ON(!endpoint->toward_ipa);
 
-	/* Delay mode doesn't work properly for IPA v4.2 */
-	if (endpoint->ipa->version != IPA_VERSION_4_2)
-		(void)ipa_endpoint_init_ctrl(endpoint, enable);
+	(void)ipa_endpoint_init_ctrl(endpoint, enable);
 }
 
 static bool ipa_endpoint_aggr_active(struct ipa_endpoint *endpoint)
@@ -355,26 +353,29 @@ ipa_endpoint_program_suspend(struct ipa_endpoint *endpoint, bool enable)
 	return suspended;
 }
 
-/* Enable or disable delay or suspend mode on all modem endpoints */
+/* Put all modem RX endpoints into suspend mode, and stop transmission
+ * on all modem TX endpoints.  Prior to IPA v4.2, endpoint DELAY mode is
+ * used for TX endpoints; starting with IPA v4.2 we use GSI channel flow
+ * control instead.
+ */
 void ipa_endpoint_modem_pause_all(struct ipa *ipa, bool enable)
 {
 	u32 endpoint_id;
 
-	/* DELAY mode doesn't work correctly on IPA v4.2 */
-	if (ipa->version == IPA_VERSION_4_2)
-		return;
-
 	for (endpoint_id = 0; endpoint_id < IPA_ENDPOINT_MAX; endpoint_id++) {
 		struct ipa_endpoint *endpoint = &ipa->endpoint[endpoint_id];
 
 		if (endpoint->ee_id != GSI_EE_MODEM)
 			continue;
 
-		/* Set TX delay mode or RX suspend mode */
-		if (endpoint->toward_ipa)
+		if (!endpoint->toward_ipa)
+			(void)ipa_endpoint_program_suspend(endpoint, enable);
+		else if (ipa->version < IPA_VERSION_4_2)
 			ipa_endpoint_program_delay(endpoint, enable);
 		else
-			(void)ipa_endpoint_program_suspend(endpoint, enable);
+			gsi_modem_channel_flow_control(&ipa->gsi,
+						       endpoint->channel_id,
+						       enable);
 	}
 }
 
@@ -1532,10 +1533,19 @@ static void ipa_endpoint_reset(struct ipa_endpoint *endpoint)
 
 static void ipa_endpoint_program(struct ipa_endpoint *endpoint)
 {
-	if (endpoint->toward_ipa)
-		ipa_endpoint_program_delay(endpoint, false);
-	else
+	if (endpoint->toward_ipa) {
+		/* Newer versions of IPA use GSI channel flow control
+		 * instead of endpoint DELAY mode to prevent sending data.
+		 * Flow control is disabled for newly-allocated channels,
+		 * and we can assume flow control is not (ever) enabled
+		 * for AP TX channels.
+		 */
+		if (endpoint->ipa->version < IPA_VERSION_4_2)
+			ipa_endpoint_program_delay(endpoint, false);
+	} else {
+		/* Ensure suspend mode is off on all AP RX endpoints */
 		(void)ipa_endpoint_program_suspend(endpoint, false);
+	}
 	ipa_endpoint_init_cfg(endpoint);
 	ipa_endpoint_init_nat(endpoint);
 	ipa_endpoint_init_hdr(endpoint);