From 560c603a6df2a8df80fcc40d74f678d393a72fdf Mon Sep 17 00:00:00 2001
From: yangsong8 <yangsong8@xiaomi.com>
Date: Thu, 27 Mar 2025 21:27:19 +0800
Subject: [PATCH] driver/serial: Check again the RX buffer, then check file
 flags

The UART driver (cdcacm...) might have buffered data received, Just continue
processing the RX queue if this happens. If not, then check the file or dev
flags.

Signed-off-by: yangsong8 <yangsong8@xiaomi.com>
---
 drivers/serial/serial.c | 118 +++++++++++++++++++++-------------------
 1 file changed, 61 insertions(+), 57 deletions(-)

diff --git a/drivers/serial/serial.c b/drivers/serial/serial.c
index e29d09add3a..f7922643888 100644
--- a/drivers/serial/serial.c
+++ b/drivers/serial/serial.c
@@ -1099,63 +1099,6 @@ static ssize_t uart_readv(FAR struct file *filep, FAR struct uio *uio)
             }
         }
 
-#ifdef CONFIG_DEV_SERIAL_FULLBLOCKS
-      /* No... then we would have to wait to get receive more data.
-       * If the user has specified the O_NONBLOCK option, then just
-       * return what we have.
-       */
-
-      else if ((filep->f_oflags & O_NONBLOCK) != 0)
-        {
-          /* If nothing was transferred, then return the -EAGAIN
-           * error (not zero which means end of file).
-           */
-
-          if (recvd < 1)
-            {
-              recvd = -EAGAIN;
-            }
-
-          break;
-        }
-#else
-      /* No... the circular buffer is empty.  Have we returned anything
-       * to the caller?
-       */
-
-      else if (recvd > 0 && !(dev->tc_lflag & ICANON))
-        {
-          /* Yes.. break out of the loop and return the number of bytes
-           * received up to the wait condition.
-           */
-
-          break;
-        }
-
-      else if (filep->f_inode == 0)
-        {
-          /* File has been closed.
-           * Descriptor is not valid.
-           */
-
-          recvd = -EBADFD;
-          break;
-        }
-
-      /* No... then we would have to wait to get receive some data.
-       * If the user has specified the O_NONBLOCK option, then do not
-       * wait.
-       */
-
-      else if ((filep->f_oflags & O_NONBLOCK) != 0)
-        {
-          /* Break out of the loop returning -EAGAIN */
-
-          recvd = -EAGAIN;
-          break;
-        }
-#endif
-
       /* Otherwise we are going to have to wait for data to arrive */
 
       else
@@ -1207,6 +1150,67 @@ static ssize_t uart_readv(FAR struct file *filep, FAR struct uio *uio)
                   continue;
                 }
 
+#ifdef CONFIG_DEV_SERIAL_FULLBLOCKS
+              /* No... then we would have to wait to get receive more data.
+               * If the user has specified the O_NONBLOCK option, then just
+               * return what we have.
+               */
+
+              else if ((filep->f_oflags & O_NONBLOCK) != 0)
+                {
+                  /* If nothing was transferred, then return the -EAGAIN
+                   * error (not zero which means end of file).
+                   */
+
+                  if (recvd < 1)
+                    {
+                      recvd = -EAGAIN;
+                    }
+
+                  leave_critical_section(flags);
+                  break;
+                }
+#else
+              /* No... the circular buffer is empty.  Have we returned
+               * anything to the caller?
+               */
+
+              else if (recvd > 0 && !(dev->tc_lflag & ICANON))
+                {
+                  /* Yes.. break out of the loop and return the number
+                   * of bytes received up to the wait condition.
+                   */
+
+                  leave_critical_section(flags);
+                  break;
+                }
+
+              else if (filep->f_inode == 0)
+                {
+                  /* File has been closed.
+                   * Descriptor is not valid.
+                   */
+
+                  recvd = -EBADFD;
+                  leave_critical_section(flags);
+                  break;
+                }
+
+              /* No... then we would have to wait to get receive some data.
+               * If the user has specified the O_NONBLOCK option, then do not
+               * wait.
+               */
+
+              else if ((filep->f_oflags & O_NONBLOCK) != 0)
+                {
+                  /* Break out of the loop returning -EAGAIN */
+
+                  recvd = -EAGAIN;
+                  leave_critical_section(flags);
+                  break;
+                }
+#endif
+
 #ifdef CONFIG_SERIAL_REMOVABLE
               /* Check again if the removable device is still connected
                * while we have interrupts off.  We do not want the transition