serial: 8250: extract serial8250_THRE_test()

serial8250_do_startup() contains a stand-alone code for probing THRE.
Furthermore, the code block is conditional (port->irq and test for
UPF_NO_THRE_TEST).

Move this code to a separate function. The conditional can be evaluated
easier there -- by a simple return in the beginning. So the indentation
level lowers and the code is overall more readable now.

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20250611100319.186924-16-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index c09a90b38d8fcb5908e1d6b09acd0080754d388e..5466286bb44fc9bb69a150dc311c296fde9669af 100644 (file)
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -2199,6 +2199,54 @@ static void serial8250_set_TRG_levels(struct uart_port *port)
        }
 }
 
+static void serial8250_THRE_test(struct uart_port *port)
+{
+       struct uart_8250_port *up = up_to_u8250p(port);
+       unsigned long flags;
+       bool iir_noint1, iir_noint2;
+
+       if (!port->irq)
+               return;
+
+       if (up->port.flags & UPF_NO_THRE_TEST)
+               return;
+
+       if (port->irqflags & IRQF_SHARED)
+               disable_irq_nosync(port->irq);
+
+       /*
+        * Test for UARTs that do not reassert THRE when the transmitter is idle and the interrupt
+        * has already been cleared.  Real 16550s should always reassert this interrupt whenever the
+        * transmitter is idle and the interrupt is enabled.  Delays are necessary to allow register
+        * changes to become visible.
+        *
+        * Synchronize UART_IER access against the console.
+        */
+       uart_port_lock_irqsave(port, &flags);
+
+       wait_for_xmitr(up, UART_LSR_THRE);
+       serial_port_out_sync(port, UART_IER, UART_IER_THRI);
+       udelay(1); /* allow THRE to set */
+       iir_noint1 = serial_port_in(port, UART_IIR) & UART_IIR_NO_INT;
+       serial_port_out(port, UART_IER, 0);
+       serial_port_out_sync(port, UART_IER, UART_IER_THRI);
+       udelay(1); /* allow a working UART time to re-assert THRE */
+       iir_noint2 = serial_port_in(port, UART_IIR) & UART_IIR_NO_INT;
+       serial_port_out(port, UART_IER, 0);
+
+       uart_port_unlock_irqrestore(port, flags);
+
+       if (port->irqflags & IRQF_SHARED)
+               enable_irq(port->irq);
+
+       /*
+        * If the interrupt is not reasserted, or we otherwise don't trust the iir, setup a timer to
+        * kick the UART on a regular basis.
+        */
+       if ((!iir_noint1 && iir_noint2) || up->port.flags & UPF_BUG_THRE)
+               up->bugs |= UART_BUG_THRE;
+}
+
 int serial8250_do_startup(struct uart_port *port)
 {
        struct uart_8250_port *up = up_to_u8250p(port);
@@ -2258,49 +2306,7 @@ int serial8250_do_startup(struct uart_port *port)
        if (retval)
                goto out;
 
-       if (port->irq && !(up->port.flags & UPF_NO_THRE_TEST)) {
-               unsigned char iir1;
-
-               if (port->irqflags & IRQF_SHARED)
-                       disable_irq_nosync(port->irq);
-
-               /*
-                * Test for UARTs that do not reassert THRE when the
-                * transmitter is idle and the interrupt has already
-                * been cleared.  Real 16550s should always reassert
-                * this interrupt whenever the transmitter is idle and
-                * the interrupt is enabled.  Delays are necessary to
-                * allow register changes to become visible.
-                *
-                * Synchronize UART_IER access against the console.
-                */
-               uart_port_lock_irqsave(port, &flags);
-
-               wait_for_xmitr(up, UART_LSR_THRE);
-               serial_port_out_sync(port, UART_IER, UART_IER_THRI);
-               udelay(1); /* allow THRE to set */
-               iir1 = serial_port_in(port, UART_IIR);
-               serial_port_out(port, UART_IER, 0);
-               serial_port_out_sync(port, UART_IER, UART_IER_THRI);
-               udelay(1); /* allow a working UART time to re-assert THRE */
-               iir = serial_port_in(port, UART_IIR);
-               serial_port_out(port, UART_IER, 0);
-
-               uart_port_unlock_irqrestore(port, flags);
-
-               if (port->irqflags & IRQF_SHARED)
-                       enable_irq(port->irq);
-
-               /*
-                * If the interrupt is not reasserted, or we otherwise
-                * don't trust the iir, setup a timer to kick the UART
-                * on a regular basis.
-                */
-               if ((!(iir1 & UART_IIR_NO_INT) && (iir & UART_IIR_NO_INT)) ||
-                   up->port.flags & UPF_BUG_THRE) {
-                       up->bugs |= UART_BUG_THRE;
-               }
-       }
+       serial8250_THRE_test(port);
 
        up->ops->setup_timer(up);