serial 8250: tighten test for using backup timer
Thomas Koeller had reported an issue where a device that had been making use
of the UART_BUG_TXEN code in the 8250 driver was mistakenly being caught by
the backup timer test, causing the device to work improperly.
To fix this, tighten the test requirements to enable the backup timer
workaround.
The backup timer is really meant to catch UARTs that don't re-assert the THRE
interrupt. The expectation is that they do initially assert THRE. This patch
clarifies the test.
Signed-off-by: Alex Williamson <alex.williamson@hp.com>
Cc: Thomas Koeller <thomas@koeller.dyndns.org>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index 6d0ce64..ea41f26 100644
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -1868,6 +1868,7 @@
}
if (is_real_interrupt(up->port.irq)) {
+ unsigned char iir1;
/*
* Test for UARTs that do not reassert THRE when the
* transmitter is idle and the interrupt has already
@@ -1881,7 +1882,7 @@
wait_for_xmitr(up, UART_LSR_THRE);
serial_out_sync(up, UART_IER, UART_IER_THRI);
udelay(1); /* allow THRE to set */
- serial_in(up, UART_IIR);
+ iir1 = serial_in(up, UART_IIR);
serial_out(up, UART_IER, 0);
serial_out_sync(up, UART_IER, UART_IER_THRI);
udelay(1); /* allow a working UART time to re-assert THRE */
@@ -1894,7 +1895,7 @@
* If the interrupt is not reasserted, setup a timer to
* kick the UART on a regular basis.
*/
- if (iir & UART_IIR_NO_INT) {
+ if (!(iir1 & UART_IIR_NO_INT) && (iir & UART_IIR_NO_INT)) {
pr_debug("ttyS%d - using backup timer\n", port->line);
up->timer.function = serial8250_backup_timeout;
up->timer.data = (unsigned long)up;