bus: mhi: ep: Only send -ENOTCONN status if client driver is available

For the STOP and RESET commands, only send the channel disconnect status
-ENOTCONN if client driver is available. Otherwise, it will result in
null pointer dereference.

Cc: <stable@vger.kernel.org> # 5.19
Fixes: e8275690 ("bus: mhi: ep: Add support for processing command rings")
Signed-off-by: NManivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: NJeffrey Hugo <quic_jhugo@quicinc.com>
Link: https://lore.kernel.org/r/20221228161704.255268-4-manivannan.sadhasivam@linaro.orgSigned-off-by: NManivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

drivers/bus/mhi/ep/main.c

@@ -203,9 +203,11 @@ static int mhi_ep_process_cmd_ring(struct mhi_ep_ring *ring, struct mhi_ring_ele
 		mhi_ep_mmio_disable_chdb(mhi_cntrl, ch_id);
 
 		/* Send channel disconnect status to client drivers */
+		if (mhi_chan->xfer_cb) {
 			result.transaction_status = -ENOTCONN;
 			result.bytes_xferd = 0;
 			mhi_chan->xfer_cb(mhi_chan->mhi_dev, &result);
+		}
 
 		/* Set channel state to STOP */
 		mhi_chan->state = MHI_CH_STATE_STOP;
@@ -235,9 +237,11 @@ static int mhi_ep_process_cmd_ring(struct mhi_ep_ring *ring, struct mhi_ring_ele
 		mhi_ep_ring_reset(mhi_cntrl, ch_ring);
 
 		/* Send channel disconnect status to client driver */
+		if (mhi_chan->xfer_cb) {
 			result.transaction_status = -ENOTCONN;
 			result.bytes_xferd = 0;
 			mhi_chan->xfer_cb(mhi_chan->mhi_dev, &result);
+		}
 
 		/* Set channel state to DISABLED */
 		mhi_chan->state = MHI_CH_STATE_DISABLED;