This is a note to let you know that I've just added the patch titled
serial: change the divisor latch only when prescalar actually changed
to the 2.6.38-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
serial-change-the-divisor-latch-only-when-prescalar-actually-changed.patch
and it can be found in the queue-2.6.38 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 0d0389e5414c8950b1613e8bdc74289cde3d6d98 Mon Sep 17 00:00:00 2001
From: Yin Kangkai <[email protected]>
Date: Wed, 9 Feb 2011 11:35:18 +0800
Subject: serial: change the divisor latch only when prescalar actually changed
From: Yin Kangkai <[email protected]>
commit 0d0389e5414c8950b1613e8bdc74289cde3d6d98 upstream.
In 8250.c original ns16550 autoconfig code, we change the divisor latch when
we goto to high speed mode, we're assuming the previous speed is legacy. This
some times is not true.
For example in a system with both CONFIG_SERIAL_8250 and
CONFIG_SERIAL_8250_PNP set, in this case, the code (autoconfig) will be called
twice, one in serial8250_init/probe() and the other is from
serial_pnp_probe. When serial_pnp_probe calls the autoconfig for NS16550A,
it's already in high speed mode, change the divisor latch (quot << 3) in this
case will make the UART console garbled.
CC: Greg Kroah-Hartman <[email protected]>
CC: David Woodhouse <[email protected]>
CC: [email protected]
Signed-off-by: Yin Kangkai <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
drivers/tty/serial/8250.c | 32 ++++++++++++++++++++------------
1 file changed, 20 insertions(+), 12 deletions(-)
--- a/drivers/tty/serial/8250.c
+++ b/drivers/tty/serial/8250.c
@@ -954,6 +954,23 @@ static int broken_efr(struct uart_8250_p
return 0;
}
+static inline int ns16550a_goto_highspeed(struct uart_8250_port *up)
+{
+ unsigned char status;
+
+ status = serial_in(up, 0x04); /* EXCR2 */
+#define PRESL(x) ((x) & 0x30)
+ if (PRESL(status) == 0x10) {
+ /* already in high speed mode */
+ return 0;
+ } else {
+ status &= ~0xB0; /* Disable LOCK, mask out PRESL[01] */
+ status |= 0x10; /* 1.625 divisor for baud_base --> 921600 */
+ serial_outp(up, 0x04, status);
+ }
+ return 1;
+}
+
/*
* We know that the chip has FIFOs. Does it have an EFR? The
* EFR is located in the same register position as the IIR and
@@ -1025,12 +1042,8 @@ static void autoconfig_16550a(struct uar
quot = serial_dl_read(up);
quot <<= 3;
- status1 = serial_in(up, 0x04); /* EXCR2 */
- status1 &= ~0xB0; /* Disable LOCK, mask out PRESL[01] */
- status1 |= 0x10; /* 1.625 divisor for baud_base -->
921600 */
- serial_outp(up, 0x04, status1);
-
- serial_dl_write(up, quot);
+ if (ns16550a_goto_highspeed(up))
+ serial_dl_write(up, quot);
serial_outp(up, UART_LCR, 0);
@@ -3025,15 +3038,10 @@ void serial8250_resume_port(int line)
struct uart_8250_port *up = &serial8250_ports[line];
if (up->capabilities & UART_NATSEMI) {
- unsigned char tmp;
-
/* Ensure it's still in high speed mode */
serial_outp(up, UART_LCR, 0xE0);
- tmp = serial_in(up, 0x04); /* EXCR2 */
- tmp &= ~0xB0; /* Disable LOCK, mask out PRESL[01] */
- tmp |= 0x10; /* 1.625 divisor for baud_base --> 921600 */
- serial_outp(up, 0x04, tmp);
+ ns16550a_goto_highspeed(up);
serial_outp(up, UART_LCR, 0);
up->port.uartclk = 921600*16;
Patches currently in stable-queue which might be from
[email protected] are
queue-2.6.38/serial-change-the-divisor-latch-only-when-prescalar-actually-changed.patch
queue-2.6.38/serial-also-set-the-uartclk-value-in-resume-after-goes-to-highspeed.patch
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