From 644a0cd52573070082d2431d9e1f81a09de57fc9 Mon Sep 17 00:00:00 2001
From: Julian Oes <julian@oes.ch>
Date: Thu, 29 Apr 2021 14:23:15 +0200
Subject: [PATCH] drivers/serial: fix Rx interrupt enable for cdcacm

This is addressing an issue where Rx interrupts were not restored for
cdcacm after the buffer had been filled (in a burst).
The Rx interrupts were only restored after the watchdog timeout of 200ms
fired.

This happened because CONFIG_SERIAL_RXDMA was set, however, for the
cdcacm driver this does not actually matter as it is relying on
uart_enablerxint to be called via the ops table.

This patch makes sure that uart_enablerxint and uart_disablerxint are
always called, independent of CONFIG_SERIAL_RXDMA, relying on the ops
table to be correct for the case where it should be only a no-op.
---
 drivers/serial/serial.c | 19 ++++---------------
 1 file changed, 4 insertions(+), 15 deletions(-)

diff --git a/drivers/serial/serial.c b/drivers/serial/serial.c
index ea64a7c07e..b33d1fa80a 100644
--- a/drivers/serial/serial.c
+++ b/drivers/serial/serial.c
@@ -900,17 +900,13 @@ static ssize_t uart_read(FAR struct file *filep,
 
       else
         {
-#ifdef CONFIG_SERIAL_RXDMA
-          /* Disable all interrupts and test again...
-           * uart_disablerxint() is insufficient for the check in DMA mode.
-           */
+          /* Disable all interrupts and test again... */
 
           flags = enter_critical_section();
-#else
+
           /* Disable Rx interrupts and test again... */
 
           uart_disablerxint(dev);
-#endif
 
           /* If the Rx ring buffer still empty?  Bytes may have been added
            * between the last time that we checked and when we disabled
@@ -927,14 +923,12 @@ static ssize_t uart_read(FAR struct file *filep,
               /* Notify DMA that there is free space in the RX buffer */
 
               uart_dmarxfree(dev);
-#else
+#endif
               /* Wait with the RX interrupt re-enabled.  All interrupts are
                * disabled briefly to assure that the following operations
                * are atomic.
                */
 
-              flags = enter_critical_section();
-
               /* Re-enable UART Rx interrupts */
 
               uart_enablerxint(dev);
@@ -952,7 +946,6 @@ static ssize_t uart_read(FAR struct file *filep,
                   leave_critical_section(flags);
                   continue;
                 }
-#endif
 
 #ifdef CONFIG_SERIAL_REMOVABLE
               /* Check again if the removable device is still connected
@@ -1020,11 +1013,9 @@ static ssize_t uart_read(FAR struct file *filep,
                * the loop.
                */
 
-#ifdef CONFIG_SERIAL_RXDMA
               leave_critical_section(flags);
-#else
+
               uart_enablerxint(dev);
-#endif
             }
         }
     }
@@ -1037,11 +1028,9 @@ static ssize_t uart_read(FAR struct file *filep,
   leave_critical_section(flags);
 #endif
 
-#ifndef CONFIG_SERIAL_RXDMA
   /* RX interrupt could be disabled by RX buffer overflow. Enable it now. */
 
   uart_enablerxint(dev);
-#endif
 
 #ifdef CONFIG_SERIAL_IFLOWCONTROL
 #ifdef CONFIG_SERIAL_IFLOWCONTROL_WATERMARKS