This is a note to let you know that I've just added the patch titled
serial: 8250: enable UART_BUG_NOMSR for Tegra
to my tty git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-next branch.
The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)
The patch will also be merged in the next major kernel release
during the merge window.
If you have any questions about this process, please let me know.
>From 3685f19e07802ec4207b52465c408f185b66490e Mon Sep 17 00:00:00 2001
From: Stephen Warren <swarren@xxxxxxxxxx>
Date: Tue, 7 Jan 2014 15:00:12 -0700
Subject: serial: 8250: enable UART_BUG_NOMSR for Tegra
Tegra chips have 4 or 5 identical UART modules embedded. UARTs C..E have
their MODEM-control signals tied off to a static state. However UARTs A
and B can optionally route those signals to/from package pins, depending
on the exact pinmux configuration.
When these signals are not routed to package pins, false interrupts may
trigger either temporarily, or permanently, all while not showing up in
the IIR; it will read as NO_INT. This will eventually lead to the UART
IRQ being disabled due to unhandled interrupts. When this happens, the
kernel may print e.g.:
irq 68: nobody cared (try booting with the "irqpoll" option)
In order to prevent this, enable UART_BUG_NOMSR. This prevents
UART_IER_MSI from being enabled, which prevents the false interrupts
from triggering.
In practice, this is not needed under any of the following conditions:
* On Tegra chips after Tegra30, since the HW bug has apparently been
fixed.
* On UARTs C..E since their MODEM control signals are tied to the correct
static state which doesn't trigger the issue.
* On UARTs A..B if the MODEM control signals are routed out to package
pins, since they will then carry valid signals.
However, we ignore these exceptions for now, since they are only relevant
if a board actually hooks up more than a 4-wire UART, and no currently
supported board does this. If we ever support a board that does, we can
refine the algorithm that enables UART_BUG_NOMSR to take those exceptions
into account, and/or read a flag from DT/... that indicates that the
board has hooked up and pinmux'd more than a 4-wire UART.
Reported-by: Olof Johansson <olof@xxxxxxxxx> # autotester
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Stephen Warren <swarren@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/serial/8250/8250_core.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index e33d38cb170f..61ecd709a722 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -2670,6 +2670,10 @@ static void serial8250_config_port(struct uart_port *port, int flags)
if (port->type == PORT_16550A && port->iotype == UPIO_AU)
up->bugs |= UART_BUG_NOMSR;
+ /* HW bugs may trigger IRQ while IIR == NO_INT */
+ if (port->type == PORT_TEGRA)
+ up->bugs |= UART_BUG_NOMSR;
+
if (port->type != PORT_UNKNOWN && flags & UART_CONFIG_IRQ)
autoconfig_irq(up);
--
1.8.5.1.163.gd7aced9
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