Hi Prarit, On 07/08/2015 08:53 AM, Prarit Bhargava wrote: > > > 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. For debugging purposes, can you use a kernel built with CONFIG_SERIAL_8250_DETECT_IRQ=n? What is the platform and device type? Regards, Peter Hurley > 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
