kernel/linux.git/include/linux/serial_core.h, branch v4.4.269

serial: core: Allow processing sysrq at port unlock time

2019-12-21T09:34:25+00:00

[ Upstream commit d6e1935819db0c91ce4a5af82466f3ab50d17346 ] Right now serial drivers process sysrq keys deep in their character receiving code. This means that they've already grabbed their port->lock spinlock. This can end up getting in the way if we've go to do serial stuff (especially kgdb) in response to the sysrq. Serial drivers have various hacks in them to handle this. Looking at '8250_port.c' you can see that the console_write() skips locking if we're in the sysrq handler. Looking at 'msm_serial.c' you can see that the port lock is dropped around uart_handle_sysrq_char(). It turns out that these hacks aren't exactly perfect. If you have lockdep turned on and use something like the 8250_port hack you'll get a splat that looks like: WARNING: possible circular locking dependency detected [...] is trying to acquire lock: ... (console_owner){-.-.}, at: console_unlock+0x2e0/0x5e4 but task is already holding lock: ... (&port_lock_key){-.-.}, at: serial8250_handle_irq+0x30/0xe4 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&port_lock_key){-.-.}: _raw_spin_lock_irqsave+0x58/0x70 serial8250_console_write+0xa8/0x250 univ8250_console_write+0x40/0x4c console_unlock+0x528/0x5e4 register_console+0x2c4/0x3b0 uart_add_one_port+0x350/0x478 serial8250_register_8250_port+0x350/0x3a8 dw8250_probe+0x67c/0x754 platform_drv_probe+0x58/0xa4 really_probe+0x150/0x294 driver_probe_device+0xac/0xe8 __driver_attach+0x98/0xd0 bus_for_each_dev+0x84/0xc8 driver_attach+0x2c/0x34 bus_add_driver+0xf0/0x1ec driver_register+0xb4/0x100 __platform_driver_register+0x60/0x6c dw8250_platform_driver_init+0x20/0x28 ... -> #0 (console_owner){-.-.}: lock_acquire+0x1e8/0x214 console_unlock+0x35c/0x5e4 vprintk_emit+0x230/0x274 vprintk_default+0x7c/0x84 vprintk_func+0x190/0x1bc printk+0x80/0xa0 __handle_sysrq+0x104/0x21c handle_sysrq+0x30/0x3c serial8250_read_char+0x15c/0x18c serial8250_rx_chars+0x34/0x74 serial8250_handle_irq+0x9c/0xe4 dw8250_handle_irq+0x98/0xcc serial8250_interrupt+0x50/0xe8 ... other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&port_lock_key); lock(console_owner); lock(&port_lock_key); lock(console_owner); *** DEADLOCK *** The hack used in 'msm_serial.c' doesn't cause the above splats but it seems a bit ugly to unlock / lock our spinlock deep in our irq handler. It seems like we could defer processing the sysrq until the end of the interrupt handler right after we've unlocked the port. With this scheme if a whole batch of sysrq characters comes in one irq then we won't handle them all, but that seems like it should be a fine compromise. Signed-off-by: Douglas Anderson Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin

serial: core: Fix unused variable warnings from uart_console()

2015-05-06T20:27:00+00:00

If CONFIG_SERIAL_CORE_CONSOLE=n, build warnings are generated by uart_console() macro expansion: drivers/tty/serial/of_serial.c: In function ‘of_serial_suspend_8250’: drivers/tty/serial/of_serial.c:262:20: warning: unused variable ‘port’ [-Wunused-variable] struct uart_port *port = &port8250->port; ^ drivers/tty/serial/of_serial.c: In function ‘of_serial_resume_8250’: drivers/tty/serial/of_serial.c:272:20: warning: unused variable ‘port’ [-Wunused-variable] struct uart_port *port = &port8250->port; Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman

earlycon: Fix __earlycon_table stride

2015-04-10T12:39:53+00:00

The compiler and the linker must agree on the alignment of struct earlycon_id; empirical testing and commit 07fca0e57fca92 ("tracing: Properly align linker defined symbols") suggests 32-byte alignment is the LCD. Reported-by: Yinghai Lu Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman

serial: 8250: allow specifying iomem size in addition to address

2015-03-26T21:50:15+00:00

This adds a mapsize field to struct uart_port to be used in conjunction with mapbase. If set, it overrides whatever value serial8250_port_size() would otherwise report. Signed-off-by: Mans Rullgard Signed-off-by: Greg Kroah-Hartman

serial: earlycon: Enable earlycon without command line param

2015-03-26T16:25:27+00:00

Earlycon matching can only be triggered if 'earlycon=...' has been specified on the kernel command line. To workaround this limitation requires tight coupling between arches and specific serial drivers in order to start an earlycon. Devicetree avoids this limitation with a link table that contains the required data to match earlycons. Mirror this approach for earlycon match by name. Re-purpose EARLYCON_DECLARE to generate a table entry which associates name with setup() function. Re-purpose setup_earlycon() to scan this table for an earlycon match, which is registered if found. Declare one "earlycon" early_param, which calls setup_earlycon(). This design allows setup_earlycon() to be called directly with a param string (as if 'earlycon=...' had been set on the command line). Re-registration (either directly or by early_param) is prevented. Acked-by: Rob Herring Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman

serial: core: Add minor field to uart_port

2015-03-26T15:10:11+00:00

UART drivers that share ttyS namespace cannot trivially compute the ttyS index from the port->line value since the minor_start may be offset from minor 64. Further, to do so requires a pointer to the uart driver since there is no back pointer from uart_port to uart_driver. Rather than have UART drivers computing the minor value by themselves, encapsulate within the serial core at port registration time. Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman

Merge 4.0-rc3 into tty-testing

2015-03-09T06:08:37+00:00

This resolves a merge issue in drivers/tty/serial/8250/8250_pci.c Signed-off-by: Greg Kroah-Hartman

serial: earlycon: Refactor parse_options into serial core

2015-03-07T02:55:07+00:00

Prepare to support console-defined matching; refactor the command line parameter string processing from parse_options() into a new core function, uart_parse_earlycon(), which decodes command line parameters of the form: earlycon=,io|mmio|mmio32,, console=,io|mmio|mmio32,, earlycon=,0x, console=,0x, Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman

serial: uapi: Declare all userspace-visible io types

2015-03-07T02:39:55+00:00

ioctl(TIOCGSERIAL|TIOCSSERIAL) report and can change the port->iotype. UART drivers use the UPIO_* definitions, but the uapi header defines parallel values and userspace uses these parallel values for ioctls; thus the userspace values are definitive. Define UPIO_* iotypes in terms of the uapi defines, SERIAL_IO_*; extend the uapi defines to include all values in use by the serial core. Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman

serial: core: Fix iotype userspace breakage

2015-03-07T02:39:55+00:00

commit 3ffb1a8193bea ("serial: core: Add big-endian iotype") re-numbered userspace-dependent values; ioctl(TIOCSSERIAL) can assign the port iotype (which is expected to match the selected i/o accessors), so iotype values must not be changed. Cc: Kevin Cernekee Cc: # 3.19+ Signed-off-by: Peter Hurley Reviewed-by: Kevin Cernekee Signed-off-by: Greg Kroah-Hartman