From 363f66fe06c75270b669c88e321e6b354ba0201e Mon Sep 17 00:00:00 2001 From: Will Newton Date: Tue, 2 Sep 2008 14:35:44 -0700 Subject: [PATCH] 8250: improve workaround for UARTs that don't re-assert THRE correctly 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 Acked-by: Alex Williamson Cc: Alan Cox Cc: David Brownell Cc: [2.6.26.x] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/serial/8250.c | 16 ++++++++++++---- drivers/serial/8250.h | 1 + 2 files changed, 13 insertions(+), 4 deletions(-) diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c index 342e12fb1c25..9ccc563d8730 100644 --- a/drivers/serial/8250.c +++ b/drivers/serial/8250.c @@ -1908,14 +1908,22 @@ 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 diff --git a/drivers/serial/8250.h b/drivers/serial/8250.h index 78c00162b04e..520260326f3d 100644 --- a/drivers/serial/8250.h +++ b/drivers/serial/8250.h @@ -47,6 +47,7 @@ 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) -- 2.20.1