From: Kumar Gala <galak@kernel.crashing.org>
To: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: linuxppc-dev@lists.ozlabs.org, linux-serial@vger.kernel.org
Subject: Re: [PATCH] 8250: add workaround for MPC8[356]xx UART break IRQ storm
Date: Fri, 26 Feb 2010 13:42:39 -0600 [thread overview]
Message-ID: <EB2B2912-24C3-46C9-B894-0A84D593570F@kernel.crashing.org> (raw)
In-Reply-To: <1267212301-26851-1-git-send-email-paul.gortmaker@windriver.com>
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.
>=20
> Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
> ---
>=20
> 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.
>=20
> 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(-)
>=20
> 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)
>=20
> status =3D serial_inp(up, UART_LSR);
>=20
> + if ((up->bugs & UART_BUG_PPC) && (status =3D=3D =
UART_LSR_RFE_ERROR_BITS)) {
> + spin_unlock_irqrestore(&up->port.lock, flags);
> + return;
> + }
> +
> DEBUG_INTR("status =3D %x...", status);
>=20
> if (status & (UART_LSR_DR | UART_LSR_BI))
> @@ -1948,6 +1953,7 @@ static int serial8250_startup(struct uart_port =
*port)
>=20
> up->capabilities =3D uart_config[up->port.type].flags;
> up->mcr =3D 0;
> + up->bugs |=3D UART_KNOWN_BUGS;
>=20
> if (up->port.iotype !=3D 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 */
>=20
> #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
>=20
> If unsure, say N.
>=20
> +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=
next prev parent reply other threads:[~2010-02-26 19:42 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-26 19:25 [PATCH] 8250: add workaround for MPC8[356]xx UART break IRQ storm Paul Gortmaker
2010-02-26 19:42 ` Kumar Gala [this message]
2010-02-26 20:21 ` Paul Gortmaker
2010-02-26 20:23 ` Scott Wood
2010-03-01 21:23 ` Paul Gortmaker
2010-03-01 23:03 ` vb
2010-03-02 16:27 ` Paul Gortmaker
2010-03-02 21:21 ` vb
2011-11-24 8:14 ` Kumar Gala
2011-11-24 15:26 ` Paul Gortmaker
2011-11-24 19:07 ` Kumar Gala
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