spi: Don't mark message DMA mapped when no transfer in it is

BugLink: https://bugs.launchpad.net/bugs/2072617

[ Upstream commit 9f788ba ]

There is no need to set the DMA mapped flag of the message if it has
no mapped transfers. Moreover, it may give the code a chance to take
the wrong paths, i.e. to exercise DMA related APIs on unmapped data.
Make __spi_map_msg() to bail earlier on the above mentioned cases.

Fixes: 99adef3 ("spi: Provide core support for DMA mapping transfers")
Signed-off-by: Andy Shevchenko <[email protected]>
Link: https://msgid.link/r/[email protected]
Signed-off-by: Mark Brown <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
Signed-off-by: Portia Stephens <[email protected]>
Signed-off-by: Stefan Bader <[email protected]>

Author: andy-shev

drivers/spi/spi.c

@@ -1047,6 +1047,7 @@ static int __spi_map_msg(struct spi_controller *ctlr, struct spi_message *msg)
 	else
 		rx_dev = ctlr->dev.parent;
 
+	ret = -ENOMSG;
 	list_for_each_entry(xfer, &msg->transfers, transfer_list) {
 		if (!ctlr->can_dma(ctlr, msg->spi, xfer))
 			continue;
@@ -1070,6 +1071,9 @@ static int __spi_map_msg(struct spi_controller *ctlr, struct spi_message *msg)
 			}
 		}
 	}
+	/* No transfer has been mapped, bail out with success */
+	if (ret)
+		return 0;
 
 	ctlr->cur_msg_mapped = true;