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authorWill Newton <will.newton@gmail.com>2008-09-03 02:35:06 +0000
committerGreg Kroah-Hartman <gregkh@suse.de>2008-09-08 04:44:20 -0700
commitda924e49a005cdb4bac9a958f3edff958b770069 (patch)
treeaba1a76095ce8aadc8d03a06bf5d7183598065f9 /drivers
parentcd9295c8b95d690c47f5f0000e3128960de8cd8b (diff)
8250: improve workaround for UARTs that don't re-assert THRE correctly
commit 363f66fe06c75270b669c88e321e6b354ba0201e upstream Recent changes to tighten the check for UARTs that don't correctly re-assert THRE (01c194d9278efc15d4785ff205643e9c0bdcef53: "serial 8250: tighten test for using backup timer") caused problems when such a UART was opened for the second time - the bug could only successfully be detected at first initialization. For users of this version of this particular UART IP it is fatal. This patch stores the information about the bug in the bugs field of the port structure when the port is first started up so subsequent opens can check this bit even if the test for the bug fails. David Brownell: "My own exposure to this is that the UART on DaVinci hardware, which TI allegedly derived from its original 16550 logic, has periodically gone from working to unusable with the mainline 8250.c ... and back and forth a bunch. Currently it's "unusable", a regression from some previous versions. With this patch from Will, it's usable." Signed-off-by: Will Newton <will.newton@gmail.com> Acked-by: Alex Williamson <alex.williamson@hp.com> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Cc: David Brownell <david-b@pacbell.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/serial/8250.c16
-rw-r--r--drivers/serial/8250.h1
2 files changed, 13 insertions, 4 deletions
diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index be95e55b228b..405084505a9f 100644
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -1895,15 +1895,23 @@ static int serial8250_startup(struct uart_port *port)
* kick the UART on a regular basis.
*/
if (!(iir1 & UART_IIR_NO_INT) && (iir & UART_IIR_NO_INT)) {
+ up->bugs |= UART_BUG_THRE;
pr_debug("ttyS%d - using backup timer\n", port->line);
- up->timer.function = serial8250_backup_timeout;
- up->timer.data = (unsigned long)up;
- mod_timer(&up->timer, jiffies +
- poll_timeout(up->port.timeout) + HZ / 5);
}
}
/*
+ * The above check will only give an accurate result the first time
+ * the port is opened so this value needs to be preserved.
+ */
+ if (up->bugs & UART_BUG_THRE) {
+ up->timer.function = serial8250_backup_timeout;
+ up->timer.data = (unsigned long)up;
+ mod_timer(&up->timer, jiffies +
+ poll_timeout(up->port.timeout) + HZ / 5);
+ }
+
+ /*
* If the "interrupt" for this port doesn't correspond with any
* hardware interrupt, we use a timer-based system. The original
* driver used to do this with IRQ0.
diff --git a/drivers/serial/8250.h b/drivers/serial/8250.h
index 91bd28f2bb47..245288d83dec 100644
--- a/drivers/serial/8250.h
+++ b/drivers/serial/8250.h
@@ -49,6 +49,7 @@ struct serial8250_config {
#define UART_BUG_QUOT (1 << 0) /* UART has buggy quot LSB */
#define UART_BUG_TXEN (1 << 1) /* UART has buggy TX IIR status */
#define UART_BUG_NOMSR (1 << 2) /* UART has buggy MSR status bits (Au1x00) */
+#define UART_BUG_THRE (1 << 3) /* UART has buggy THRE reassertion */
#define PROBE_RSA (1 << 0)
#define PROBE_ANY (~0)