Re: [PATCH] 8250: add workaround for MPC8[356]xx UART break IRQ storm

[vb@vsbe.com]

sounds very much like this issue:

http://linux.derkeiler.com/Mailing-Lists/Kernel/2010-02/msg09470.html

(interrupt storm on the second port which is hit with breaks).

It's not the uart driver problem per se, the below fixes it:

*** linux/drivers/serial/serial_core.c#1        Wed Feb 24 17:46:22 2010
---  linux/drivers/serial/serial_core.c#2        Mon Mar  1 15:00:29 2010
***************
*** 622,632 ****
        struct uart_port *port = state->port;

        if (I_IXOFF(tty)) {
                if (port->x_char)
                        port->x_char = 0;
!               else
                        uart_send_xchar(tty, START_CHAR(tty));
        }

        if (tty->termios->c_cflag & CRTSCTS)
                uart_set_mctrl(port, TIOCM_RTS);
--- 622,632 ----
        struct uart_port *port = state->port;

        if (I_IXOFF(tty)) {
                if (port->x_char)
                        port->x_char = 0;
!               else if (!(tty->flags & (1 << TTY_IO_ERROR)))
                        uart_send_xchar(tty, START_CHAR(tty));
        }

        if (tty->termios->c_cflag & CRTSCTS)
                uart_set_mctrl(port, TIOCM_RTS);
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I did not get to trying to submit it, but it sure gets rid o the storm.

cheers,
/vb

On Fri, Feb 26, 2010 at 11:25 AM, Paul Gortmaker
<paul.gortmaker@windriver.com> wrote:
> Sending a break on the SOC UARTs found in some MPC83xx/85xx/86xx
> chips seems to cause a short lived IRQ storm (/proc/interrupts
> typically shows somewhere between 300 and 1500 events).  Unfortunately
> this renders SysRQ over the serial console completely inoperable.
> Testing with obvious things like ACKing the event doesn't seem to
> change anything vs. a completely dumb approach of just ignoring
> it and waiting for it to stop, so that is what is implemented here.
>
> Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
> ---
>
> This is a refresh of a patch I'd done earlier -- I've tried to make
> the bug support as generic as possible to minimize having board
> specific ifdef crap in 8250.c -- any suggestions on how to further
> improve it are welcome.
>
>  drivers/serial/8250.c      |    6 ++++++
>  drivers/serial/8250.h      |   20 ++++++++++++++++++++
>  drivers/serial/Kconfig     |   14 ++++++++++++++
>  include/linux/serial_reg.h |    2 ++
>  4 files changed, 42 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
> index e9b15c3..850b0e9 100644
> --- a/drivers/serial/8250.c
> +++ b/drivers/serial/8250.c
> @@ -1531,6 +1531,11 @@ static void serial8250_handle_port(struct uart_8250_port *up)
>
>        status = serial_inp(up, UART_LSR);
>
> +       if ((up->bugs & UART_BUG_PPC) && (status == UART_LSR_RFE_ERROR_BITS)) {
> +               spin_unlock_irqrestore(&up->port.lock, flags);
> +               return;
> +       }
> +
>        DEBUG_INTR("status = %x...", status);
>
>        if (status & (UART_LSR_DR | UART_LSR_BI))
> @@ -1948,6 +1953,7 @@ static int serial8250_startup(struct uart_port *port)
>
>        up->capabilities = uart_config[up->port.type].flags;
>        up->mcr = 0;
> +       up->bugs |= UART_KNOWN_BUGS;
>
>        if (up->port.iotype != up->cur_iotype)
>                set_io_from_upio(port);
> diff --git a/drivers/serial/8250.h b/drivers/serial/8250.h
> index 6e19ea3..2074ce1 100644
> --- a/drivers/serial/8250.h
> +++ b/drivers/serial/8250.h
> @@ -49,6 +49,7 @@ struct serial8250_config {
>  #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 UART_BUG_PPC   (1 << 4)        /* UART has buggy PPC break IRQ storm */
>
>  #define PROBE_RSA      (1 << 0)
>  #define PROBE_ANY      (~0)
> @@ -78,3 +79,22 @@ struct serial8250_config {
>  #else
>  #define ALPHA_KLUDGE_MCR 0
>  #endif
> +
> +/*
> + * The following UART bugs are currently dynamically detected and not
> + * required to be contingent on any particular compile time options.
> + */
> +#define HAS_BUG_QUOT   0       /* assign UART_BUG_QUOT to enable */
> +#define HAS_BUG_TXEN   0       /* assign UART_BUG_TXEN to enable */
> +#define HAS_BUG_NOMSR  0       /* assign UART_BUG_NOMSR to enable */
> +#define HAS_BUG_THRE   0       /* assign UART_BUG_THRE to enable */
> +
> +#ifdef CONFIG_SERIAL_8250_PPC_BUG
> +#define HAS_BUG_PPC    UART_BUG_PPC
> +#else
> +#define HAS_BUG_PPC    0
> +#endif
> +
> +#define UART_KNOWN_BUGS (HAS_BUG_QUOT | HAS_BUG_TXEN | HAS_BUG_NOMSR | \
> +                       HAS_BUG_THRE | HAS_BUG_PPC)
> +
> diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
> index 9ff47db..e01a411 100644
> --- a/drivers/serial/Kconfig
> +++ b/drivers/serial/Kconfig
> @@ -70,6 +70,20 @@ config SERIAL_8250_CONSOLE
>
>          If unsure, say N.
>
> +config SERIAL_8250_PPC_BUG
> +       bool "Fix 8250/16550 to handle IRQ storm after receipt of a break"
> +       depends on SERIAL_8250 && PPC32
> +       ---help---
> +         If you say Y here, addional checks will be added in the handling of
> +         interrupts on the serial ports which will prevent ill effects of
> +         an interrupt storm triggered by a break on the serial line. Without
> +         this enabled, a Sysrq via the serial console can be unusable on
> +         some systems.
> +
> +         This is commonly observed on PPC32 MPC83xx/85xx/86xx based boards.
> +
> +         If unsure, say N.
> +
>  config FIX_EARLYCON_MEM
>        bool
>        depends on X86
> diff --git a/include/linux/serial_reg.h b/include/linux/serial_reg.h
> index cf9327c..010174f 100644
> --- a/include/linux/serial_reg.h
> +++ b/include/linux/serial_reg.h
> @@ -111,6 +111,7 @@
>  #define UART_MCR_DTR           0x01 /* DTR complement */
>
>  #define UART_LSR       5       /* In:  Line Status Register */
> +#define UART_LSR_RFE           0x80 /* Rx FIFO Error (BE, FE, or PE) */
>  #define UART_LSR_TEMT          0x40 /* Transmitter empty */
>  #define UART_LSR_THRE          0x20 /* Transmit-hold-register empty */
>  #define UART_LSR_BI            0x10 /* Break interrupt indicator */
> @@ -119,6 +120,7 @@
>  #define UART_LSR_OE            0x02 /* Overrun error indicator */
>  #define UART_LSR_DR            0x01 /* Receiver data ready */
>  #define UART_LSR_BRK_ERROR_BITS        0x1E /* BI, FE, PE, OE bits */
> +#define UART_LSR_RFE_ERROR_BITS        0xF1 /* RFE, TEMT, THRE, BI, DR bits */
>
>  #define UART_MSR       6       /* In:  Modem Status Register */
>  #define UART_MSR_DCD           0x80 /* Data Carrier Detect */
> --
> 1.6.5.2
>
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