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From:   Jeffrey Hugo <jhugo@codeaurora.org>
To:     manivannan.sadhasivam@linaro.org, hemantk@codeaurora.org
Cc:     bbhatt@codeaurora.org, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org, Jeffrey Hugo <jhugo@codeaurora.org>
Subject: [PATCH] mhi_bus: core: Wait for ready state after reset
Date:   Tue, 16 Feb 2021 13:52:25 -0700
Message-Id: <1613508745-32324-1-git-send-email-jhugo@codeaurora.org>
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After the device has signaled the end of reset by clearing the reset bit,
it will automatically reinit MHI and the internal device structures.  Once
That is done, the device will signal it has entered the ready state.

Signaling the ready state involves sending an interrupt (MSI) to the host
which might cause IOMMU faults if it occurs at the wrong time.

If the controller is being powered down, and possibly removed, then the
reset flow would only wait for the end of reset.  At which point, the host
and device would start a race.  The host may complete its reset work, and
remove the interrupt handler, which would cause the interrupt to be
disabled in the IOMMU.  If that occurs before the device signals the ready
state, then the IOMMU will fault since it blocked an interrupt.  While
harmless, the fault would appear like a serious issue has occurred so let's
silence it by making sure the device hits the ready state before the host
completes its reset processing.

Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>
---
 drivers/bus/mhi/core/pm.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
index ef8fb4a..dc69074 100644
--- a/drivers/bus/mhi/core/pm.c
+++ b/drivers/bus/mhi/core/pm.c
@@ -463,7 +463,7 @@ static void mhi_pm_disable_transition(struct mhi_controller *mhi_cntrl)
 
 	/* Trigger MHI RESET so that the device will not access host memory */
 	if (!MHI_PM_IN_FATAL_STATE(mhi_cntrl->pm_state)) {
-		u32 in_reset = -1;
+		u32 in_reset = -1, ready = 0;
 		unsigned long timeout = msecs_to_jiffies(mhi_cntrl->timeout_ms);
 
 		dev_dbg(dev, "Triggering MHI Reset in device\n");
@@ -486,6 +486,25 @@ static void mhi_pm_disable_transition(struct mhi_controller *mhi_cntrl)
 		 * hence re-program it
 		 */
 		mhi_write_reg(mhi_cntrl, mhi_cntrl->bhi, BHI_INTVEC, 0);
+
+		if (!MHI_IN_PBL(mhi_get_exec_env(mhi_cntrl))) {
+			/* wait for ready to be set */
+			ret = wait_event_timeout(mhi_cntrl->state_event,
+						 mhi_read_reg_field(mhi_cntrl,
+							mhi_cntrl->regs,
+							MHISTATUS,
+							MHISTATUS_READY_MASK,
+							MHISTATUS_READY_SHIFT,
+							&ready)
+						 || ready, timeout);
+			if ((!ret || !ready) &&
+			    cur_state == MHI_PM_SYS_ERR_PROCESS) {
+				dev_err(dev,
+					"Device failed to enter READY state\n");
+				mutex_unlock(&mhi_cntrl->pm_mutex);
+				return;
+			}
+		}
 	}
 
 	dev_dbg(dev,
-- 
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