This is a note to let you know that I've just added the patch titled
serial: 8250_dw: Report CTS asserted for auto flow
to the 3.10-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-8250_dw-report-cts-asserted-for-auto-flow.patch
and it can be found in the queue-3.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 33acbb82695f84e9429c1f7fbdeb4588dea12ffa Mon Sep 17 00:00:00 2001
From: Tim Kryger <[email protected]>
Date: Fri, 16 Aug 2013 13:50:15 -0700
Subject: serial: 8250_dw: Report CTS asserted for auto flow
From: Tim Kryger <[email protected]>
commit 33acbb82695f84e9429c1f7fbdeb4588dea12ffa upstream.
When a serial port is configured for RTS/CTS flow control, serial core
will disable the transmitter if it observes CTS is de-asserted. This is
perfectly reasonable and appropriate when the UART lacks the ability to
automatically perform CTS flow control.
However, if the UART hardware can manage flow control automatically, it
is important that software not get involved. When the DesignWare UART
enables 16C750 style auto-RTS/CTS it stops generating interrupts for
changes in CTS state so software mostly stays out of the way. However,
it does report the true state of CTS in the MSR so software may notice
it is de-asserted and respond by improperly disabling the transmitter.
Once this happens the transmitter will be blocked forever.
To avoid this situation, we simply lie to the 8250 and serial core by
reporting that CTS is asserted whenever auto-RTS/CTS mode is enabled.
Signed-off-by: Tim Kryger <[email protected]>
Reviewed-by: Matt Porter <[email protected]>
Reviewed-by: Markus Mayer <[email protected]>
Cc: Wang Nan <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
drivers/tty/serial/8250/8250_dw.c | 34 ++++++++++++++++++++++++++--------
1 file changed, 26 insertions(+), 8 deletions(-)
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -55,10 +55,24 @@
struct dw8250_data {
int last_lcr;
+ int last_mcr;
int line;
struct clk *clk;
};
+static inline int dw8250_modify_msr(struct uart_port *p, int offset, int value)
+{
+ struct dw8250_data *d = p->private_data;
+
+ /* If reading MSR, report CTS asserted when auto-CTS/RTS enabled */
+ if (offset == UART_MSR && d->last_mcr & UART_MCR_AFE) {
+ value |= UART_MSR_CTS;
+ value &= ~UART_MSR_DCTS;
+ }
+
+ return value;
+}
+
static void dw8250_serial_out(struct uart_port *p, int offset, int value)
{
struct dw8250_data *d = p->private_data;
@@ -66,15 +80,17 @@ static void dw8250_serial_out(struct uar
if (offset == UART_LCR)
d->last_lcr = value;
- offset <<= p->regshift;
- writeb(value, p->membase + offset);
+ if (offset == UART_MCR)
+ d->last_mcr = value;
+
+ writeb(value, p->membase + (offset << p->regshift));
}
static unsigned int dw8250_serial_in(struct uart_port *p, int offset)
{
- offset <<= p->regshift;
+ unsigned int value = readb(p->membase + (offset << p->regshift));
- return readb(p->membase + offset);
+ return dw8250_modify_msr(p, offset, value);
}
static void dw8250_serial_out32(struct uart_port *p, int offset, int value)
@@ -84,15 +100,17 @@ static void dw8250_serial_out32(struct u
if (offset == UART_LCR)
d->last_lcr = value;
- offset <<= p->regshift;
- writel(value, p->membase + offset);
+ if (offset == UART_MCR)
+ d->last_mcr = value;
+
+ writel(value, p->membase + (offset << p->regshift));
}
static unsigned int dw8250_serial_in32(struct uart_port *p, int offset)
{
- offset <<= p->regshift;
+ unsigned int value = readl(p->membase + (offset << p->regshift));
- return readl(p->membase + offset);
+ return dw8250_modify_msr(p, offset, value);
}
static int dw8250_handle_irq(struct uart_port *p)
Patches currently in stable-queue which might be from [email protected] are
queue-3.10/serial-8250_dw-report-cts-asserted-for-auto-flow.patch
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