Thanks your beautiful explain for edge interrupt handler, still has one confusing for unmask_irq in irq_finalize_oneshot().
Could you see below comments? Thanks. > -----Original Message----- > From: Thomas Gleixner [mailto:t...@linutronix.de] > Sent: Friday, October 12, 2012 9:48 PM > To: Liu, Chuansheng > Cc: linux-kernel@vger.kernel.org > Subject: RE: [PATCH] genirq: for edge interrupt IRQS_ONESHOT support with irq > thread > > On Fri, 12 Oct 2012, Liu, Chuansheng wrote: > > > -----Original Message----- > > > From: Thomas Gleixner [mailto:t...@linutronix.de] > > > Sent: Friday, October 12, 2012 8:46 PM > > > To: Liu, Chuansheng > > > Cc: linux-kernel@vger.kernel.org > > > Subject: RE: [PATCH] genirq: for edge interrupt IRQS_ONESHOT support > with irq > > > thread > > > > > > On Fri, 12 Oct 2012, Liu, Chuansheng wrote: > > > > > -----Original Message----- > > > > > From: Thomas Gleixner [mailto:t...@linutronix.de] > > > > > Sent: Friday, October 12, 2012 8:32 PM > > > > > To: Liu, Chuansheng > > > > > Cc: linux-kernel@vger.kernel.org > > > > > Subject: Re: [PATCH] genirq: for edge interrupt IRQS_ONESHOT support > > > with irq > > > > > thread > > > > > > > > > > On Fri, 12 Oct 2012, Chuansheng Liu wrote: > > > > > > > > > > > > In our system, there is one edge interrupt, and we want it to be > > > > > > irq thread with IRQS_ONESHOT, and found in handle_edge_irq(), > > > > > > even with IRQS_ONESHOT, the irq is still unmasked without care of > > > > > > flag IRQS_ONESHOT. > > > > > > > > > > > > It causes IRQS_ONESHOT can not work well for edge interrupt, but > also > > > > > > after the irq thread finished with flag IRQS_ONESHOT, the irq will > > > > > > be > > > > > > possible to be unmasked again, it should be messing mask/unmask > logic. > > > > > > > > > > This is just wrong. By masking edge interrupts you will run into > > > > > situations where you will lose interrupts. > > > > > > > > > > Can you please explain, why you want to mask your edge interrupt? > > > > > > > When I request_irq with irq thread handler and flag IRQS_ONESHOT, if > > > > do not mask the edge interrupt, the primary handler and irq thread > > > > maybe run at the same time, and in my real case it causes spin > > > > deadlock. > > > > > > Then your code is simply wrong and you need to fix it instead of hacking a > > > workaround into the core code. Locking is not that hard. > > > > I got means, so I want to use flag IRQS_ONESHOT to avoid the case that two > > handlers running at the same time. Is it right direction? > > Again, this does not work for edge type interrupts. Period. And we are > not adding something which is known to be broken. > > Also there is no problem when a hard interrupt comes in while the > thread handler is running. It's just a matter of proper code and > proper locking. > > > But IRQS_ONESHOT does not work well for edge interrupt. > > And pasting the IRQS_ONESHOT description: > > * IRQS_ONESHOT - irq is not unmasked in primary handler > > Right, and edge type interrupts doe not support it. Can we do something? Thanks your sharing. In request_thread_irq() case with FLAG IRQS_ONESHOT, for edge interrupt, in function irq_finalize_oneshot(): if (!desc->threads_oneshot && !irqd_irq_disabled(&desc->irq_data) && irqd_irq_masked(&desc->irq_data)) unmask_irq(desc); It is possible unmask_irq() is called, but the below code is just aiming for masking action in irq handler, so I guess if I called the mask_irq() in non-core code, when irq_finalize_oneshot is called, the unmask_irq is called, and it is not we wanted, right? Do not test this case:) > > > And I need irq handler is because some heavy work is needed, it can avoid > local > > irq disabling time thru irq handler. > > Disable the interrupt at the device level in your primary handler, but > do not try to impose something to the core code which is fundamentaly > wrong. > > > > > > > > You means it is not right with IRQS_ONESHOT for edge interrupt? > > > > > > It's wrong. Simnply because you can lose interrupts. > > > > > > interrupt raised > > > handle_edge_irq() > > > mask_ack_irq() > > > handle_event() > > > wake irq thread > > > reti > > > > > > irq thread runs > > > handle device interrupt() > > > <--- device issues edge irq > > > unmask_irq() > > > > > > This interrupt is not delivered. So your device stops working. Not > > > what you want, right? > > > Device should not stop:) And even in current handle_edge_irq(), it > > is possible that losting Interrupt if primary handler need some time > > and the irq is quick enough. I says the below code, it just avoid > > The code flow is: > > Interrupt > ack() > handler() > RETI > > After the ack another interrupt can come in. It's raised in the CPU, > but it cannot be delivered because the CPU is running that very > interrupt at this point with interupts disabled. After RETI this > interrupt is delivered and runs the edge handler again. That's on UP. > > On SMP an interrupt which is raised after the ack() again before the > handler finishes, can invoke another delivery on a different CPU, > which then sees the IRQ_INPROGESS flag, masks it and flags it > PENDING. When the primary handler on the first CPU returns, it sees > the PENDING flag, unmasks and invokes the handler another time. > Got it. Thanks your clear explain. > So nothing gets lost. Now you mask it and if you look at the flow I > showed in my last mail, then your device will be stuck. Simply because > the interrupt was delivered while the line was masked at the irq chip > level which causes a drop. That's a property of edge type interrupts > and we have proper code to deal with it. No way to change that just > that you can avoid to fix your broken driver design. > > Thanks, > > tglx > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
