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Message-ID: <53209475.2040805@redhat.com>
Date: Wed, 12 Mar 2014 18:08:05 +0100
From: Hans de Goede <hdegoede@...hat.com>
To: Thomas Gleixner <tglx@...utronix.de>
CC: LKML <linux-kernel@...r.kernel.org>,
Carlo Caione <carlo.caione@...il.com>,
Russell King <linux@....linux.org.uk>,
Maxime Ripard <maxime.ripard@...e-electrons.com>
Subject: Re: [PATCH] irq: Add a new IRQF_ACK_BEFORE_UNMASK irq flag
Hi,
On 03/12/2014 11:38 AM, Thomas Gleixner wrote:
> On Wed, 12 Mar 2014, Hans de Goede wrote:
<snip>
> And how is that different from the non threaded case?
>
> mask()
> ack() <-- irq line is still active
> handle() <-- irq line goes inactive. So this happens
> after the ack as above
> unmask()
>
Right as I already said in my own reply to my patch, my initial analysis
was wrong.
>> Note that things work fine without this patch, the purpose of this patch is
>> soley to avoid the second unneeded interrupt.
>>
>> This patch uses an interrupt flag for this and not an irqchip flag because
>> the need for ack before unmask is based on the device and not on the irqchip.
>
> No, it's not a device property. Its an irq chip property.
Agreed.
<snip>
> If the interrupt chip has this behaviour then handle_level_irq as the
> flow handler is the wrong thing to start with because it always acks
> before calling the handler.
>
> Due to the fact that we run the primary handler with interrupts
> disabled, we should avoid the mask/unmask dance for the non threaded
> case completely. handle_fasteoi_irq does that, except that it does not
> provide the eoi() before unmask in the threaded case and it has an
> extra eoi() even in the masked case which is pointless for interrupt
> chips like the one you are dealing with.
>
> Untested patch below.
Thanks, I've just finished testing this, and it works as advertised.
This indeed seems the best solution. I'm going to send a v2
of my sun4i irq patch-set with this patch included with 2 fixes added:
1) Export the prototype for the new handle_fasteoi_late_irq function
2) Fix the minor issue Russell noticed
I've only one minor nitpick wrt this patch, for ONESHOT
to work properly the irq_chip for an irq_desc using
handle_fasteoi_late_irq must set the IRQCHIP_EOI_THREADED, but
this is not enforced anywhere.
Maybe add a BUG_ON to the irq mapping code checking this ?
Thanks & Regards,
Hans
>
> Thanks,
>
> tglx
>
> ---------------->
>
> Index: linux-2.6/include/linux/irq.h
> ===================================================================
> --- linux-2.6.orig/include/linux/irq.h
> +++ linux-2.6/include/linux/irq.h
> @@ -349,6 +349,8 @@ struct irq_chip {
> * IRQCHIP_ONOFFLINE_ENABLED: Only call irq_on/off_line callbacks
> * when irq enabled
> * IRQCHIP_SKIP_SET_WAKE: Skip chip.irq_set_wake(), for this irq chip
> + * IRQCHIP_ONESHOT_SAFE: One shot does not require mask/unmask
> + * IRQCHIP_EOI_THREADED: Chip requires eoi() on unmask in threaded mode
> */
> enum {
> IRQCHIP_SET_TYPE_MASKED = (1 << 0),
> @@ -357,6 +359,7 @@ enum {
> IRQCHIP_ONOFFLINE_ENABLED = (1 << 3),
> IRQCHIP_SKIP_SET_WAKE = (1 << 4),
> IRQCHIP_ONESHOT_SAFE = (1 << 5),
> + IRQCHIP_EOI_THREADED = (1 << 6),
> };
>
> /* This include will go away once we isolated irq_desc usage to core code */
> Index: linux-2.6/kernel/irq/chip.c
> ===================================================================
> --- linux-2.6.orig/kernel/irq/chip.c
> +++ linux-2.6/kernel/irq/chip.c
> @@ -281,6 +281,19 @@ void unmask_irq(struct irq_desc *desc)
> }
> }
>
> +void unmask_threaded_irq(struct irq_desc *desc)
> +{
> + struct irq_chip *chip = desc->irq_data.chip;
> +
> + if (chip->flags & IRQCHIP_EOI_THREADED)
> + chip->irq_eoi(&desc->irq_data);
> +
> + if (chip->irq_unmask) {
> + desc->irq_data.chip->irq_unmask(&desc->irq_data);
> + irq_state_clr_masked(desc);
> + }
> +}
> +
> /*
> * handle_nested_irq - Handle a nested irq from a irq thread
> * @irq: the interrupt number
> @@ -487,6 +500,67 @@ out:
> goto out_unlock;
> }
>
> +static void cond_unmask_and_eoi_irq(struct irq_desc *desc)
> +{
> + if (!(desc->istate & IRQS_ONESHOT)) {
> + desc->irq_data.chip->irq_eoi(&desc->irq_data);
> + return;
> + }
> + /*
> + * We need to unmask in the following cases:
> + * - Oneshot irq which did not wake the thread (caused by a
> + * spurious interrupt or a primary handler handling it
> + * completely).
> + */
> + if (!irqd_irq_disabled(&desc->irq_data) &&
> + irqd_irq_masked(&desc->irq_data) && !desc->threads_oneshot) {
> + desc->irq_data.chip->irq_eoi(&desc->irq_data);
> + unmask_irq(desc);
> + }
> +}
> +
> +/**
> + * handle_fasteoi_late_irq - irq handler for transparent controllers
> + * @irq: the interrupt number
> + * @desc: the interrupt description structure for this irq
> + *
> + * Only a single callback will be issued to the chip: an ->eoi()
> + * call when the interrupt has been serviced. Same as above, but
> + * we avoid the eoi when the interrupt is masked due to a
> + * threaded handler. The eoi will be issued right before the unmask.
> + */
> +void handle_fasteoi_late_irq(unsigned int irq, struct irq_desc *desc)
> +{
> + raw_spin_lock(&desc->lock);
> +
> + if (unlikely(irqd_irq_inprogress(&desc->irq_data)))
> + if (!irq_check_poll(desc))
> + goto out;
> +
> + desc->istate &= ~(IRQS_REPLAY | IRQS_WAITING);
> + kstat_incr_irqs_this_cpu(irq, desc);
> +
> + /*
> + * If its disabled or no action available
> + * then mask it and get out of here:
> + */
> + if (unlikely(!desc->action || irqd_irq_disabled(&desc->irq_data))) {
> + desc->istate |= IRQS_PENDING;
> + mask_irq(desc);
> + goto out;
> + }
> +
> + if (desc->istate & IRQS_ONESHOT)
> + mask_irq(desc);
> +
> + handle_irq_event(desc);
> +
> + cond_unmask_and_eoi_irq(desc);
> +out:
> + raw_spin_unlock(&desc->lock);
> + return;
> +}
> +
> /**
> * handle_edge_irq - edge type IRQ handler
> * @irq: the interrupt number
> Index: linux-2.6/kernel/irq/internals.h
> ===================================================================
> --- linux-2.6.orig/kernel/irq/internals.h
> +++ linux-2.6/kernel/irq/internals.h
> @@ -73,6 +73,7 @@ extern void irq_percpu_enable(struct irq
> extern void irq_percpu_disable(struct irq_desc *desc, unsigned int cpu);
> extern void mask_irq(struct irq_desc *desc);
> extern void unmask_irq(struct irq_desc *desc);
> +extern void unmask_threaded_irq(struct irq_desc *desc);
>
> extern void init_kstat_irqs(struct irq_desc *desc, int node, int nr);
>
> Index: linux-2.6/kernel/irq/manage.c
> ===================================================================
> --- linux-2.6.orig/kernel/irq/manage.c
> +++ linux-2.6/kernel/irq/manage.c
> @@ -718,7 +718,7 @@ again:
>
> if (!desc->threads_oneshot && !irqd_irq_disabled(&desc->irq_data) &&
> irqd_irq_masked(&desc->irq_data))
> - unmask_irq(desc);
> + unmask_threaded_irq(desc);
>
> out_unlock:
> raw_spin_unlock_irq(&desc->lock);
>
--
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