[PATCH 15/33] serial: 8250: extract serial8250_THRE_test()

Jiri Slaby (SUSE)
2025-06-11T10:03:54Z

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>
---
drivers/tty/serial/8250/8250_port.c | 92 +++++++++++++++--------------
1 file changed, 49 insertions(+), 43 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index c09a90b38d8f..5466286bb44f 100644
--- 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);

--
2.49.0