On 07/08/2015 07:55 AM, Peter Hurley wrote: > Hi Taichi, > > On 06/05/2015 06:03 AM, Taichi Kageyama wrote: >> This patch provides a new parameter as a workaround of the following >> problem. It allows us to skip autoconfig_irq() and to use a well-known irq >> number for a console even if CONFIG_SERIAL_8250_DETECT_IRQ is defined. >> >> There're cases where autoconfig_irq() fails during boot. >> In these cases, the console doesn't work in interrupt mode, >> the mode cannot be changed anymore, and "input overrun" >> (which can make operation mistakes) happens easily. >> This problem happens with high rate every boot once it occurs >> because the boot sequence is always almost same. >> >> autoconfig_irq() assumes that a CPU can handle an interrupt from a serial >> during the waiting time, but there're some cases where the CPU cannot >> handle the interrupt for longer than the time. It completely depends on >> how other functions work on the CPU. Ideally, autoconfig_irq() should be >> fixed > > It completely depends on how long some other driver has interrupts disabled, > which is a problem that needs fixed _in that driver_. autoconfig_irq() does not > need fixing. > > A typical cause of this behavior is printk spew from overly-instrumented > debugging of some driver (trace_printk is better suited to heavy instrumentation). > Peter, I understand what you're saying, however the problem is that this is the serial driver which is one of, if not _the_ main debug output mechanism in the kernel. I'm not sure I agree with doing this patch, but perhaps an easier approach would be to add a debug kernel parameter like "serial.force_irq=4" to force the irq to a previously known good value? That way the issue of the broken driver can be debugged. P. > Regards, > Peter Hurley > > >> to control these cases but as long as auto_irq algorithm is used, >> it's hard to know which CPU can handle an interrupt from a serial and >> to assure the interrupt of the CPU is enabled during auto_irq. >> Meanwhile for legacy consoles, they actually don't require auto_irq >> because they basically use well-known irq number. >> For non-console serials, this workaround is not required >> because setserial command can kick autoconfig_irq() again for them. >> >> Signed-off-by: Taichi Kageyama <t-kageyama@xxxxxxxxxxxxx> >> Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> >> --- >> drivers/tty/serial/8250/8250_core.c | 17 +++++++++++++++++ >> 1 files changed, 17 insertions(+), 0 deletions(-) >> >> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c >> index 6bf31f2..60fda28 100644 >> --- a/drivers/tty/serial/8250/8250_core.c >> +++ b/drivers/tty/serial/8250/8250_core.c >> @@ -65,6 +65,8 @@ static int serial_index(struct uart_port *port) >> >> static unsigned int skip_txen_test; /* force skip of txen test at init time */ >> >> +static unsigned int skip_cons_autoirq; /* force skip autoirq for console */ >> + >> /* >> * Debugging. >> */ >> @@ -3336,6 +3338,9 @@ serial8250_register_ports(struct uart_driver *drv, struct device *dev) >> if (skip_txen_test) >> up->port.flags |= UPF_NO_TXEN_TEST; >> >> + if (uart_console(&up->port) && skip_cons_autoirq) >> + up->port.flags &= ~UPF_AUTO_IRQ; >> + >> uart_add_one_port(drv, &up->port); >> } >> } >> @@ -3875,6 +3880,9 @@ int serial8250_register_8250_port(struct uart_8250_port *up) >> if (skip_txen_test) >> uart->port.flags |= UPF_NO_TXEN_TEST; >> >> + if (uart_console(&uart->port) && skip_cons_autoirq) >> + uart->port.flags &= ~UPF_AUTO_IRQ; >> + >> if (up->port.flags & UPF_FIXED_TYPE) >> uart->port.type = up->port.type; >> >> @@ -3936,6 +3944,10 @@ void serial8250_unregister_port(int line) >> uart->port.flags &= ~UPF_BOOT_AUTOCONF; >> if (skip_txen_test) >> uart->port.flags |= UPF_NO_TXEN_TEST; >> + >> + if (uart_console(&uart->port) && skip_cons_autoirq) >> + uart->port.flags &= ~UPF_AUTO_IRQ; >> + >> uart->port.type = PORT_UNKNOWN; >> uart->port.dev = &serial8250_isa_devs->dev; >> uart->capabilities = 0; >> @@ -4044,6 +4056,9 @@ MODULE_PARM_DESC(nr_uarts, "Maximum number of UARTs supported. (1-" __MODULE_STR >> module_param(skip_txen_test, uint, 0644); >> MODULE_PARM_DESC(skip_txen_test, "Skip checking for the TXEN bug at init time"); >> >> +module_param(skip_cons_autoirq, uint, 0644); >> +MODULE_PARM_DESC(skip_cons_autoirq, "Skip auto irq for console during boot"); >> + >> #ifdef CONFIG_SERIAL_8250_RSA >> module_param_array(probe_rsa, ulong, &probe_rsa_count, 0444); >> MODULE_PARM_DESC(probe_rsa, "Probe I/O ports for RSA"); >> @@ -4070,6 +4085,8 @@ static void __used s8250_options(void) >> module_param_cb(share_irqs, ¶m_ops_uint, &share_irqs, 0644); >> module_param_cb(nr_uarts, ¶m_ops_uint, &nr_uarts, 0644); >> module_param_cb(skip_txen_test, ¶m_ops_uint, &skip_txen_test, 0644); >> + module_param_cb(skip_cons_autoirq, ¶m_ops_uint, >> + &skip_cons_autoirq, 0644); >> #ifdef CONFIG_SERIAL_8250_RSA >> __module_param_call(MODULE_PARAM_PREFIX, probe_rsa, >> ¶m_array_ops, .arr = &__param_arr_probe_rsa, >> > -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
