On Feb 26, 2010, at 1:25 PM, Paul Gortmaker 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@xxxxxxxxxxxxx>
> ---
>
> 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.
> +
is there harm caused if we have SERIAL_8250_PPC_BUG set and dont need it?
- k--
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