[PATCH v2 1/4] irq: Add handle_fasteoi_late_irq irq handler
Hans de Goede
hdegoede at redhat.com
Wed Mar 12 13:21:20 EDT 2014
Hi,
On 03/12/2014 06:17 PM, Hans de Goede wrote:
> From: Thomas Gleixner <tglx at linutronix.de>
>
> Add an irq handler for transparent controllers
>
> Only a single callback will be issued to the chip: an ->eoi() call when
> the interrupt has been serviced. Same as handle_fasteoi_irq, but
> we avoid the eoi when the interrupt is masked due to a
> threaded handler. The eoi will be issued right before the unmask.
>
> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
Oops everything below this was not intended to be part of the commit msg.
Regards,
Hans
>> In some cases we want to do an ack right before the unmask of an irq.
>>
>> A typical example of such a case is having an i2c device which uses a level
>> interrupt. Such devices usually have an interrupt status register with
>> write to clear status bits. This means that the interrupt handler needs to
>> sleep to do i2c transfers to read / write the interrupt status register.
>>
>> This means using a threaded interrupt handler and IRQF_ONESHOT so that the
>> interrupt does not re-trigger while the interrupt handler is waiting for the
>> i2c transfer.
>>
>> Without ack-before-unmask the sequence of a single interrupt in this setup
>> looks like this:
>>
>> i2c-device raises interrupt line
>> interrupt gets triggered
>> interrupt gets masked
>> interrupt gets acked
>> interrupt handling thread starts running
>> interrupt handling thread does its stuff, write-clears irq-status register
>> in i2c-device
>> i2c-device lowers interrupt line (note this happens after the ack!)
>> interrupt handling thread is done
>> interrupt gets unmasked
>> interrupt immediately retriggers again, because the line has been high
>> after the ack
>> interrupt gets masked
>> interrupt gets acked
>> interrupt handling thread starts running
>> interrupt handling thread reads irq-status register, has nothing todo
>> interrupt handling thread is done
>> interrupt gets unmasked
>>
>> So in essence we get and handle 2 interrupts for what is 1 interrupt from
>> the i2c-device pov. By doing an ack before the unmask, the second interrupt
>> is avoided since at the point of the unmask the irq-thread has done its
>> job and cleared the interrupt source.
>
> 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()
>
>> 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. There are
> interrupt chips which handle that case fine and making this a device
> property might even break such interrupt chips. e.g. ioapic handles
> that nicely but it would use ack_edge() on a level interrupt when the
> device driver requests that. And the edge and level mode of the ioapic
> are substantially different. Go figure.
>
> The general policy is that device drivers should be oblivious of the
> underlying interrupt controller implementation as much as possible.
>
> 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,
>
> tglx
>
> ---------------->
> ---
> include/linux/irq.h | 4 +++
> kernel/irq/chip.c | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++
> kernel/irq/internals.h | 1 +
> kernel/irq/manage.c | 2 +-
> 4 files changed, 79 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/irq.h b/include/linux/irq.h
> index 7dc1003..51c199e 100644
> --- a/include/linux/irq.h
> +++ b/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 */
> @@ -412,6 +415,7 @@ static inline int irq_set_parent(int irq, int parent_irq)
> */
> extern void handle_level_irq(unsigned int irq, struct irq_desc *desc);
> extern void handle_fasteoi_irq(unsigned int irq, struct irq_desc *desc);
> +extern void handle_fasteoi_late_irq(unsigned int irq, struct irq_desc *desc);
> extern void handle_edge_irq(unsigned int irq, struct irq_desc *desc);
> extern void handle_edge_eoi_irq(unsigned int irq, struct irq_desc *desc);
> extern void handle_simple_irq(unsigned int irq, struct irq_desc *desc);
> diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
> index dc04c16..bc3c099 100644
> --- a/kernel/irq/chip.c
> +++ b/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) {
> + 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 +500,66 @@ 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);
> +}
> +
> /**
> * handle_edge_irq - edge type IRQ handler
> * @irq: the interrupt number
> diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
> index 001fa5b..e98bb56 100644
> --- a/kernel/irq/internals.h
> +++ b/kernel/irq/internals.h
> @@ -73,6 +73,7 @@ extern void irq_percpu_enable(struct irq_desc *desc, unsigned int cpu);
> 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);
>
> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> index 481a13c..9147fef 100644
> --- a/kernel/irq/manage.c
> +++ b/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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