bus: mhi: core: Check state before processing power_down

We cannot process a power_down if the power state is DISABLED.  There is
no valid mhi_ctxt in that case, so attepting to process the power_down
will likely result in a null pointer dereference.  If the power state is
DISABLED, there is nothing to do anyways, so just bail early.
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/1615409365-8165-1-git-send-email-jhugo@codeaurora.orgSigned-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

drivers/bus/mhi/core/pm.c

@@ -1134,6 +1134,7 @@ int mhi_async_power_up(struct mhi_controller *mhi_cntrl)
 		mhi_deinit_dev_ctxt(mhi_cntrl);
 
 error_dev_ctxt:
+	mhi_cntrl->pm_state = MHI_PM_DISABLE;
 	mutex_unlock(&mhi_cntrl->pm_mutex);
 
 	return ret;
@@ -1145,12 +1146,19 @@ void mhi_power_down(struct mhi_controller *mhi_cntrl, bool graceful)
 	enum mhi_pm_state cur_state, transition_state;
 	struct device *dev = &mhi_cntrl->mhi_dev->dev;
 
+	mutex_lock(&mhi_cntrl->pm_mutex);
+	write_lock_irq(&mhi_cntrl->pm_lock);
+	cur_state = mhi_cntrl->pm_state;
+	if (cur_state == MHI_PM_DISABLE) {
+		write_unlock_irq(&mhi_cntrl->pm_lock);
+		mutex_unlock(&mhi_cntrl->pm_mutex);
+		return; /* Already powered down */
+	}
+
 	/* If it's not a graceful shutdown, force MHI to linkdown state */
 	transition_state = (graceful) ? MHI_PM_SHUTDOWN_PROCESS :
 			   MHI_PM_LD_ERR_FATAL_DETECT;
 
-	mutex_lock(&mhi_cntrl->pm_mutex);
-	write_lock_irq(&mhi_cntrl->pm_lock);
 	cur_state = mhi_tryset_pm_state(mhi_cntrl, transition_state);
 	if (cur_state != transition_state) {
 		dev_err(dev, "Failed to move to state: %s from: %s\n",