This is to fix an issue where output will suddenly become very slow.
The problem occurs on 8250 UARTS with the hardware bug UART_BUG_THRE.
BACKGROUND
For normal UARTs (without UART_BUG_THRE): When the serial core layer
gets new transmit data and the transmitter is idle, it buffers the
data and calls the 8250s' serial8250_start_tx() routine which will
simply enable the TX interrupt in the IER register and return. This
should immediately fire a THRE interrupt and begin transmitting the
data.
For buggy UARTs (with UART_BUG_THRE): merely enabling the TX interrupt
in IER does not necessarily generate a new THRE interrupt.
Therefore, a background timer periodically checks to see if there is
pending data, and starts transmission if that is the case.
The bug happens on SMP systems when the system has nothing to transmit,
the transmit interrupt is disabled and the following sequence occurs:
- CPU0: The background timer routine serial8250_backup_timeout()
starts and saves the state of the interrupt enable register (IER)
and then disables all interrupts in IER. NOTE: The transmit interrupt
(TI) bit is saved as disabled.
- CPU1: The serial core gets data to transmit, grabs the port lock and
calls serial8250_start_tx() which enables the TI in IER.
- CPU0: serial8250_backup_timeout() waits for the port lock.
- CPU1: finishes (with TI enabled) and releases the port lock.
- CPU0: serial8250_backup_timeout() calls the interrupt routine which
will transmit the next fifo's worth of data and then restores the
IER from the previously saved value (TI disabled).
At this point, as long as the serial core has more transmit data
buffered, it will not call serial8250_start_tx() again and the
background timer routine will slowly transmit the data.
The fix is to have serial8250_start_tx() get the port lock before
it saves the IER state and release it after restoring IER. This will
prevent serial8250_start_tx() from running in parallel.
Signed-off-by: Al Cooper <alcooperx@gmail.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
* 'tty-next' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty-2.6: (26 commits)
amba pl011: workaround for uart registers lockup
n_gsm: fix the wrong FCS handling
pch_uart: add missing comment about OKI ML7223
pch_uart: Add MSI support
tty: fix "IRQ45: nobody cared"
PTI feature to allow user to name and mark masterchannel request.
0 for o PTI Makefile bug.
tty: serial: samsung.c remove legacy PM code.
SERIAL: SC26xx: Fix link error.
serial: mrst_max3110: initialize waitqueue earlier
mrst_max3110: Change max missing message priority.
tty: s5pv210: Add delay loop on fifo reset function for UART
tty/serial: Fix XSCALE serial ports, e.g. ce4100
serial: bfin_5xx: fix off-by-one with resource size
drivers/tty: use printk_ratelimited() instead of printk_ratelimit()
tty: n_gsm: Added refcount usage to gsm_mux and gsm_dlci structs
tty: n_gsm: Add raw-ip support
tty: n_gsm: expose gsmtty device nodes at ldisc open time
pch_phub: Fix register miss-setting issue
serial: 8250, increase PASS_LIMIT
...
Commit 4539c24fe4 "tty/serial: Add
explicit PORT_TEGRA type" introduced separate flags describing the need
for IER bits UUE and RTOIE. Both bits are required for the XSCALE port
type. While that patch updated uart_config[] as required, the auto-probing
code wasn't updated to set the RTOIE flag when an XSCALE port type was
detected. This caused such ports to stop working. This patch rectifies
that.
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Cc: stable <stable@kernel.org> [3.0]
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
With virtual machines like qemu, it's pretty common to see "too much
work for irq4" messages nowadays. This happens when a bunch of output
is printed on the emulated serial console. This is caused by too low
PASS_LIMIT. When ISR loops more than the limit, it spits the message.
I've been using a kernel with doubled the limit and I couldn't see no
problems. Maybe it's time to get rid of the message now?
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
When changing the port type, the capabilities flags should be changed
also, otherwise the capabilities will not correspond to the port type,
which make set_sleep() crash on rmmod.
This patch just assign the correct capabilites when the port changes.
Signed-off-by: Breno Leitao <leitao@linux.vnet.ibm.com>
CC: Michael Reed <mreed@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
When a break is received, Tegra's UART apparently fills the FIFO with
0 bytes. These must be drained so that they aren't interpreted as actual
data received. This allows e.g. MAGIC_SYSRQ to work on Tegra's UARTs.
v2: Added FIXME comment to clear_rx_fifo
Originally-by: Laxman Dewangan <ldewangan@nvidia.com>
Cc: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Tegra's UART is currently auto-detected as PORT_XSCALE due to register
bit UART_IER.UUE being writable. However, the Tegra documentation states
that this register bit is reserved. Hence, we should not program it.
Instead, the documentation specifies that the UART is 16550 compatible.
However, Tegra does need register bit UART_IER.RTOIE set, which is not
enabled by any 16550 port type. This was not noticed before, since
PORT_XSCALE enables CAP_UUE, which conflates both UUE and RTOIE bit
programming.
This change defines PORT_TEGRA that doesn't set UART_CAP_UUE, but does
set UART_CAP_RTOIE, which is a new capability indicating that the RTOIE
bit needs to be enabled.
Based-on-code-by: Laxman Dewangan <ldewangan@nvidia.com>
Cc: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
remove invalid location line in each file header after location
moved from driver/char to driver/tty
Signed-off-by: Jovi Zhang <bookjovi@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
In 8250.c original ns16550 autoconfig code, we change the divisor latch when
we goto to high speed mode, we're assuming the previous speed is legacy. This
some times is not true.
For example in a system with both CONFIG_SERIAL_8250 and
CONFIG_SERIAL_8250_PNP set, in this case, the code (autoconfig) will be called
twice, one in serial8250_init/probe() and the other is from
serial_pnp_probe. When serial_pnp_probe calls the autoconfig for NS16550A,
it's already in high speed mode, change the divisor latch (quot << 3) in this
case will make the UART console garbled.
CC: Greg Kroah-Hartman <greg@kroah.com>
CC: David Woodhouse <dwmw2@infradead.org>
CC: linux-kernel@vger.kernel.org
CC: stable@kernel.org
Signed-off-by: Yin Kangkai <kangkai.yin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
For any reason if the NS16550A was not work in high speed mode (e.g. we hold
NS16550A from going to high speed mode in autoconfig_16550a()), now we are
resume from suspend, we should also set the uartclk to the correct
value. Otherwise it is still the old 1843200 and that will bring issues.
CC: Greg Kroah-Hartman <greg@kroah.com>
CC: David Woodhouse <dwmw2@infradead.org>
CC: linux-kernel@vger.kernel.org
CC: stable@kernel.org
Signed-off-by: Yin Kangkai <kangkai.yin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Unbreak Billionton CF bluetooth card. This actually fixes a regression
on zaurus.
Signed-off-by: Pavel Machek <pavel@ucw.cz>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
The serial drivers are really just tty drivers, so move them to
drivers/tty/ to make things a bit neater overall.
This is part of the tty/serial driver movement proceedure as proposed by
Arnd Bergmann and approved by everyone involved a number of months ago.
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Rogier Wolff <R.E.Wolff@bitwizard.nl>
Cc: Michael H. Warfield <mhw@wittsend.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
