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authorStephen Warren <swarren@nvidia.com>2014-01-07 15:00:12 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-01-07 17:14:24 -0800
commit3685f19e07802ec4207b52465c408f185b66490e (patch)
tree866053c4a674ae365f64a6238b4ebd2c6512f05a /drivers/tty
parentbb7e73c598fb226c75f7625088a8f6a45a0fc892 (diff)
downloadlinux-3685f19e07802ec4207b52465c408f185b66490e.tar.bz2
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@lixom.net> # autotester Cc: <stable@vger.kernel.org> Signed-off-by: Stephen Warren <swarren@nvidia.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty')
-rw-r--r--drivers/tty/serial/8250/8250_core.c4
1 files changed, 4 insertions, 0 deletions
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);