litex_serial: use small lock in arch/risc-v/src/litex/litex_serial.c

reason:
We hope to remove all instances of spin_lock_irqsave(NULL).

Signed-off-by: hujun5 <[email protected]>

arch/risc-v/src/litex/litex_serial.c

@@ -124,6 +124,7 @@ struct up_dev_s
   uintptr_t uartbase; /* Base address of UART registers */
   uint32_t  baud;     /* Configured baud */
   uint8_t   irq;      /* IRQ associated with this UART */
+  spinlock_t lock;    /* Spinlock */
   uint8_t   im;       /* Interrupt mask state */
 };
 
@@ -190,6 +191,7 @@ static struct up_dev_s g_uart0priv =
   .uartbase  = LITEX_UART0_BASE,
   .baud      = CONFIG_UART0_BAUD,
   .irq       = LITEX_IRQ_UART0,
+  .lock      = SP_UNLOCKED,
 };
 
 static uart_dev_t g_uart0port =
@@ -240,15 +242,15 @@ static void up_serialout(struct up_dev_s *priv, int offset, uint32_t value)
 
 static void up_restoreuartint(struct up_dev_s *priv, uint8_t im)
 {
-  irqstate_t flags = spin_lock_irqsave(NULL);
+  irqstate_t flags = spin_lock_irqsave(&priv->lock);
 
   priv->im = im;
 
   putreg8(getreg8(LITEX_CONSOLE_BASE + UART_EV_PENDING_OFFSET), \
                     LITEX_CONSOLE_BASE + UART_EV_PENDING_OFFSET);
   up_serialout(priv, UART_EV_ENABLE_OFFSET, im);
 
-  spin_unlock_irqrestore(NULL, flags);
+  spin_unlock_irqrestore(&priv->lock, flags);
 }
 
 /****************************************************************************
@@ -257,7 +259,7 @@ static void up_restoreuartint(struct up_dev_s *priv, uint8_t im)
 
 static void up_disableuartint(struct up_dev_s *priv, uint8_t *im)
 {
-  irqstate_t flags = spin_lock_irqsave(NULL);
+  irqstate_t flags = spin_lock_irqsave(&priv->lock);
 
   /* Return the current interrupt mask value */
 
@@ -274,7 +276,7 @@ static void up_disableuartint(struct up_dev_s *priv, uint8_t *im)
                     LITEX_CONSOLE_BASE + UART_EV_PENDING_OFFSET);
   up_serialout(priv, UART_EV_ENABLE_OFFSET, 0);
 
-  spin_unlock_irqrestore(NULL, flags);
+  spin_unlock_irqrestore(&priv->lock, flags);
 }
 
 /****************************************************************************