[PATCH 3.19 105/177] serial: 8250: Revert "tty: serial: 8250_core: read only RX if there is something in the FIFO"

[Greg Kroah-Hartman]

3.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>

commit ca8bb4aefb932e3da105f28cbfba36d57a931081 upstream.

This reverts commit 0aa525d11859c1a4d5b78fdc704148e2ae03ae13.

The conditional RX-FIFO read seems to cause spurious interrupts and we
see just:
|serial8250: too much work for irq29

The previous behaviour was "default" for decades and Marvell's 88f6282 SoC
might not be the only that relies on it. Therefore the Omap fix is
reverted for now.

Fixes: 0aa525d11859 ("tty: serial: 8250_core: read only RX if there is
something in the FIFO")
Reported-By: Nicolas Schichan <nschichan@xxxxxxxxxx>
Debuged-By: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/tty/serial/8250/8250_core.c |   11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -2107,8 +2107,8 @@ int serial8250_do_startup(struct uart_po
 	/*
 	 * Clear the interrupt registers.
 	 */
-	if (serial_port_in(port, UART_LSR) & UART_LSR_DR)
-		serial_port_in(port, UART_RX);
+	serial_port_in(port, UART_LSR);
+	serial_port_in(port, UART_RX);
 	serial_port_in(port, UART_IIR);
 	serial_port_in(port, UART_MSR);
 
@@ -2269,8 +2269,8 @@ dont_test_tx_en:
 	 * saved flags to avoid getting false values from polling
 	 * routines or the previous session.
 	 */
-	if (serial_port_in(port, UART_LSR) & UART_LSR_DR)
-		serial_port_in(port, UART_RX);
+	serial_port_in(port, UART_LSR);
+	serial_port_in(port, UART_RX);
 	serial_port_in(port, UART_IIR);
 	serial_port_in(port, UART_MSR);
 	up->lsr_saved_flags = 0;
@@ -2363,8 +2363,7 @@ void serial8250_do_shutdown(struct uart_
 	 * Read data port to reset things, and then unlink from
 	 * the IRQ chain.
 	 */
-	if (serial_port_in(port, UART_LSR) & UART_LSR_DR)
-		serial_port_in(port, UART_RX);
+	serial_port_in(port, UART_RX);
 	serial8250_rpm_put(up);
 
 	del_timer_sync(&up->timer);


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