[PATCH v1 1/6] bus: mhi: core: Improve shutdown handling after link down detection

[Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>]

If MHI were to attempt a device shutdown following an assumption
that the device is inaccessible, the host currently moves to a state
where device register accesses are allowed when they should not be.
This would end up allowing accesses to device register space when the
link is inaccessible which can result in NOC errors to be observed on
the host. Improve shutdown handling so as to prevent these outcomes
and do not move the MHI PM state to a register accessible state after
device is assumed to be inaccessible.

Signed-off-by: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>
---
 drivers/bus/mhi/core/init.c     |  1 +
 drivers/bus/mhi/core/internal.h |  1 +
 drivers/bus/mhi/core/pm.c       | 20 ++++++++++++++------
 3 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/drivers/bus/mhi/core/init.c b/drivers/bus/mhi/core/init.c
index 9b6a5173..0ae4c34 100644
--- a/drivers/bus/mhi/core/init.c
+++ b/drivers/bus/mhi/core/init.c
@@ -37,6 +37,7 @@
 	[DEV_ST_TRANSITION_MISSION_MODE] = "MISSION_MODE",
 	[DEV_ST_TRANSITION_SYS_ERR] = "SYS_ERR",
 	[DEV_ST_TRANSITION_DISABLE] = "DISABLE",
+	[DEV_ST_TRANSITION_FATAL] = "FATAL SHUTDOWN",
 };
 
 const char * const mhi_state_str[MHI_STATE_MAX] = {
diff --git a/drivers/bus/mhi/core/internal.h b/drivers/bus/mhi/core/internal.h
index 798aa483..a7203c2 100644
--- a/drivers/bus/mhi/core/internal.h
+++ b/drivers/bus/mhi/core/internal.h
@@ -388,6 +388,7 @@ enum dev_st_transition {
 	DEV_ST_TRANSITION_MISSION_MODE,
 	DEV_ST_TRANSITION_SYS_ERR,
 	DEV_ST_TRANSITION_DISABLE,
+	DEV_ST_TRANSITION_FATAL,
 	DEV_ST_TRANSITION_MAX,
 };
 
diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
index 783e3d5..b2b3de7 100644
--- a/drivers/bus/mhi/core/pm.c
+++ b/drivers/bus/mhi/core/pm.c
@@ -37,9 +37,10 @@
  *     M0 -> FW_DL_ERR
  *     M0 -> M3_ENTER -> M3 -> M3_EXIT --> M0
  * L1: SYS_ERR_DETECT -> SYS_ERR_PROCESS --> POR
- * L2: SHUTDOWN_PROCESS -> DISABLE
+ * L2: SHUTDOWN_PROCESS -> LD_ERR_FATAL_DETECT
+ *     SHUTDOWN_PROCESS -> DISABLE
  * L3: LD_ERR_FATAL_DETECT <--> LD_ERR_FATAL_DETECT
- *     LD_ERR_FATAL_DETECT -> SHUTDOWN_PROCESS
+ *     LD_ERR_FATAL_DETECT -> DISABLE
  */
 static struct mhi_pm_transitions const dev_state_transitions[] = {
 	/* L0 States */
@@ -72,7 +73,7 @@
 	{
 		MHI_PM_M3,
 		MHI_PM_M3_EXIT | MHI_PM_SYS_ERR_DETECT |
-		MHI_PM_SHUTDOWN_PROCESS | MHI_PM_LD_ERR_FATAL_DETECT
+		MHI_PM_LD_ERR_FATAL_DETECT
 	},
 	{
 		MHI_PM_M3_EXIT,
@@ -103,7 +104,7 @@
 	/* L3 States */
 	{
 		MHI_PM_LD_ERR_FATAL_DETECT,
-		MHI_PM_LD_ERR_FATAL_DETECT | MHI_PM_SHUTDOWN_PROCESS
+		MHI_PM_LD_ERR_FATAL_DETECT | MHI_PM_DISABLE
 	},
 };
 
@@ -667,7 +668,11 @@ void mhi_pm_st_worker(struct work_struct *work)
 			break;
 		case DEV_ST_TRANSITION_DISABLE:
 			mhi_pm_disable_transition
-				(mhi_cntrl, MHI_PM_SHUTDOWN_PROCESS);
+					(mhi_cntrl, MHI_PM_SHUTDOWN_PROCESS);
+			break;
+		case DEV_ST_TRANSITION_FATAL:
+			mhi_pm_disable_transition
+					(mhi_cntrl, MHI_PM_LD_ERR_FATAL_DETECT);
 			break;
 		default:
 			break;
@@ -1040,6 +1045,7 @@ int mhi_async_power_up(struct mhi_controller *mhi_cntrl)
 void mhi_power_down(struct mhi_controller *mhi_cntrl, bool graceful)
 {
 	enum mhi_pm_state cur_state;
+	enum dev_st_transition next_state = DEV_ST_TRANSITION_DISABLE;
 	struct device *dev = &mhi_cntrl->mhi_dev->dev;
 
 	/* If it's not a graceful shutdown, force MHI to linkdown state */
@@ -1054,9 +1060,11 @@ void mhi_power_down(struct mhi_controller *mhi_cntrl, bool graceful)
 			dev_dbg(dev, "Failed to move to state: %s from: %s\n",
 				to_mhi_pm_state_str(MHI_PM_LD_ERR_FATAL_DETECT),
 				to_mhi_pm_state_str(mhi_cntrl->pm_state));
+		else
+			next_state = DEV_ST_TRANSITION_FATAL;
 	}
 
-	mhi_queue_state_transition(mhi_cntrl, DEV_ST_TRANSITION_DISABLE);
+	mhi_queue_state_transition(mhi_cntrl, next_state);
 
 	/* Wait for shutdown to complete */
 	flush_work(&mhi_cntrl->st_worker);
-- 
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