Give a general overview of the facility at the top of file and add copyright notice. Signed-off-by: Tejun Heo <tj@xxxxxxxxxx> --- kernel/irq/spurious.c | 74 ++++++++++++++++++++++++++++++++++++++++++++++++- 1 files changed, 73 insertions(+), 1 deletions(-) diff --git a/kernel/irq/spurious.c b/kernel/irq/spurious.c index 2d92113..329555f 100644 --- a/kernel/irq/spurious.c +++ b/kernel/irq/spurious.c @@ -2,8 +2,66 @@ * linux/kernel/irq/spurious.c * * Copyright (C) 1992, 1998-2004 Linus Torvalds, Ingo Molnar + * Copyright (C) 2010 SUSE Linux Products GmbH + * Copyright (C) 2010 Tejun Heo <tj@xxxxxxxxxx> * - * This file contains spurious interrupt handling. + * There are two ways interrupt handling can go wrong - too few or too + * many. Due to misrouting or other issues, sometimes IRQs don't + * reach the driver while at other times an interrupt line gets stuck + * and a continuous spurious interrupts are generated. + * + * This file implements workaround for both cases. Lost interrupts + * are handled by IRQ expecting and watching, and spurious interrupts + * by spurious polling. All mechanisms need IRQF_SHARED to be set on + * the irqaction in question. + * + * Both lost interrupt workarounds require cooperation from drivers + * and can be chosen depending on how much information the driver can + * provide. + * + * - IRQ expecting + * + * IRQ expecting is useful when the driver can tell when IRQs can be + * expected; in other words, when IRQs are used to signal completion + * of host initiated operations. This is the surest way to work + * around lost interrupts. + * + * When the controller is expected to raise an IRQ, the driver + * should call expect_irq() and, when the expected event happens or + * times out, unexpect_irq(). IRQ subsystem polls the interrupt + * inbetween. + * + * As interrupts tend to keep working if it works at the beginning, + * IRQ expecting implements "verified state". After certain number + * of successful IRQ deliveries, the irqaction becomes verified and + * much longer polling interval is used. + * + * - IRQ watching + * + * This can be used when the driver doesn't know when to exactly + * expect and unexpect IRQs. Once watch_irq() is called, the + * irqaction is slowly polled for certain amount of time (1min). If + * IRQs are missed during that time, the irqaction is marked and + * actively polled; otherwise, the watching is stopped. + * + * In the most basic case, drivers can call this right after + * registering an irqaction to verify IRQ delivery. In many cases, + * if IRQ works at the beginning, it keeps working, so just calling + * watch_irq() once can provide decent protection against misrouted + * IRQs. It would also be a good idea to call watch_irq() when + * timeouts are detected. + * + * - Spurious IRQ handling + * + * All IRQs are continuously monitored and spurious IRQ handling + * kicks in if there are too many spurious IRQs. The IRQ is + * disabled and the registered irqactions are polled. The IRQ is + * given another shot after certain number IRQs are handled or an + * irqaction is added or removed. + * + * All of the above three mechanisms can be used together. Spurious + * IRQ handling is enabled by default and drivers are free to expect + * and watch IRQs as they see fit. */ #include <linux/jiffies.h> @@ -17,6 +75,20 @@ #include "internals.h" +/* + * I spent quite some time thinking about each parameter but they + * still are just numbers pulled out of my ass. If you think your ass + * is prettier than mine, please go ahead and suggest better ones. + * + * Most parameters are intentionally fixed constants and not + * adjustable through API. The nature of IRQ delivery failures isn't + * usually dependent on specific drivers and the timing parameters are + * more about human perceivable latencies rather than any specific + * controller timing details, so figuring out constant values which + * can work for most cases shouldn't be too hard. This allows tighter + * control over polling behaviors, eases future changes and makes the + * interface easy for drivers. + */ enum { /* irqfixup levels */ IRQFIXUP_SPURIOUS = 0, /* spurious storm detection */ -- 1.6.4.2 -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html