diff --git a/drivers/serial/bfin_5xx.c b/drivers/serial/bfin_5xx.c
index 351cc03578eb..c8ca3b43487d 100644
--- a/drivers/serial/bfin_5xx.c
+++ b/drivers/serial/bfin_5xx.c
@@ -23,6 +23,7 @@
 #include <linux/tty.h>
 #include <linux/tty_flip.h>
 #include <linux/serial_core.h>
+#include <linux/dma-mapping.h>
 
 #if defined(CONFIG_KGDB_SERIAL_CONSOLE) || \
 	defined(CONFIG_KGDB_SERIAL_CONSOLE_MODULE)
@@ -33,12 +34,10 @@
 #include <asm/gpio.h>
 #include <mach/bfin_serial_5xx.h>
 
-#ifdef CONFIG_SERIAL_BFIN_DMA
-#include <linux/dma-mapping.h>
+#include <asm/dma.h>
 #include <asm/io.h>
 #include <asm/irq.h>
 #include <asm/cacheflush.h>
-#endif
 
 #ifdef CONFIG_SERIAL_BFIN_MODULE
 # undef CONFIG_EARLY_PRINTK
@@ -688,6 +687,13 @@ static int bfin_serial_startup(struct uart_port *port)
 
 # ifdef CONFIG_BF54x
 	{
+		/*
+		 * UART2 and UART3 on BF548 share interrupt PINs and DMA
+		 * controllers with SPORT2 and SPORT3. UART rx and tx
+		 * interrupts are generated in PIO mode only when configure
+		 * their peripheral mapping registers properly, which means
+		 * request corresponding DMA channels in PIO mode as well.
+		 */
 		unsigned uart_dma_ch_rx, uart_dma_ch_tx;
 
 		switch (uart->port.irq) {