[PATCH] serial: 8250: check DMA channel configuration errors

[James Hilliard <james.hilliard1@gmail.com>]

serial8250_request_dma() checks channel capabilities but ignores the
result of configuring either channel. Those checks do not establish
that the provider accepted the requested slave configuration. If it
rejects the configuration, startup still selects DMA and later attempts
transfers on a channel that was not configured successfully.

Return the configuration error after releasing the channels acquired so
far. Both the common and OMAP startup paths already fall back to PIO when
requesting DMA fails. Check configuration before allocating the receive
buffer or mapping the transmit buffer, using the existing unwind paths.

Fixes: 9ee4b83e51f7 ("serial: 8250: Add support for dmaengine")
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
---
 drivers/tty/serial/8250/8250_dma.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c
index 1da605cc8601..d6cda9a121c2 100644
--- a/drivers/tty/serial/8250/8250_dma.c
+++ b/drivers/tty/serial/8250/8250_dma.c
@@ -262,7 +262,9 @@ int serial8250_request_dma(struct uart_8250_port *p)
 		goto release_rx;
 	}
 
-	dmaengine_slave_config(dma->rxchan, &dma->rxconf);
+	ret = dmaengine_slave_config(dma->rxchan, &dma->rxconf);
+	if (ret)
+		goto release_rx;
 
 	/* Get a channel for TX */
 	dma->txchan = dma_request_slave_channel_compat(mask,
@@ -282,7 +284,9 @@ int serial8250_request_dma(struct uart_8250_port *p)
 		goto err;
 	}
 
-	dmaengine_slave_config(dma->txchan, &dma->txconf);
+	ret = dmaengine_slave_config(dma->txchan, &dma->txconf);
+	if (ret)
+		goto err;
 
 	rx_dev = dmaengine_get_dma_device(dma->rxchan);
 	tx_dev = dmaengine_get_dma_device(dma->txchan);

---
base-commit: 1184f87e2790e8af9be3116f608d2e86b4792d7d
change-id: 20261021-submit-serial-8250-dma-config-errors-v1-d536630f0c9d

Best regards,
--  
James Hilliard <james.hilliard1@gmail.com>