linux-kernel - Re: [PATCH v2 1/3] genirq/affinity: Add irq_update_affinity

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Date:   Wed, 18 Nov 2020 11:34:27 +0000
From:   John Garry <john.garry@...wei.com>
To:     Thomas Gleixner <tglx@...utronix.de>, <gregkh@...uxfoundation.org>,
        <rafael@...nel.org>, <martin.petersen@...cle.com>,
        <jejb@...ux.ibm.com>
CC:     <linuxarm@...wei.com>, <linux-scsi@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <maz@...nel.org>
Subject: Re: [PATCH v2 1/3] genirq/affinity: Add irq_update_affinity_desc()

Hi Thomas,

> 
> Sorry for the delay. 

No worries, Thanks for the effort.

> Supporting this truly on x86 needs some more
> thought and surgery, but for ARM it should not matter. 

ok, as long as you are content not to support x86 atm.

> I made a few
> tweaks to your original code. See below.

I think maybe a few more tweaks, below. Apart from that, it looks to 
work ok.

> 
> Thanks,
> 
>          tglx
> ---
> From: John Garry <john.garry@...wei.com>
> Subject: genirq/affinity: Add irq_update_affinity_desc()
> Date: Wed, 28 Oct 2020 20:33:05 +0800
> 
> From: John Garry <john.garry@...wei.com>
> 
> Add a function to allow the affinity of an interrupt be switched to
> managed, such that interrupts allocated for platform devices may be
> managed.
> 
> Suggested-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: John Garry <john.garry@...wei.com>
> ---
>   include/linux/interrupt.h |    8 ++++++
>   kernel/irq/manage.c       |   56 ++++++++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 64 insertions(+)
> 

...

> +/**
> + * irq_update_affinity_desc - Update affinity management for an interrupt
> + * @irq:	The interrupt number to update
> + * @affinity:	Pointer to the affinity descriptor
> + *
> + * This interface can be used to configure the affinity management of
> + * interrupts which have been allocated already.
> + */
> +int irq_update_affinity_desc(unsigned int irq,
> +			     struct irq_affinity_desc *affinity)

Just a note on the return value, in the only current callsite - 
platform_get_irqs_affinity() - we don't check the return value and 
propagate the error. This is because we don't want to fail the interrupt 
init just because of problems updating the affinity mask. So I could 
print a message to inform the user of error (at the callsite).

> +{
> +	struct irq_desc *desc;
> +	unsigned long flags;
> +	bool activated;
> +
> +	/*
> +	 * Supporting this with the reservation scheme used by x86 needs
> +	 * some more thought. Fail it for now.
> +	 */
> +	if (IS_ENABLED(CONFIG_GENERIC_IRQ_RESERVATION_MODE))
> +		return -EOPNOTSUPP;
> +
> +	desc = irq_get_desc_buslock(irq, &flags, 0);
> +	if (!desc)
> +		return -EINVAL;
> +
> +	/* Requires the interrupt to be shut down */
> +	if (irqd_is_started(&desc->irq_data))

We're missing the unlock here, right?

> +		return -EBUSY;
> +
> +	/* Interrupts which are already managed cannot be modified */
> +	if (irqd_is_managed(&desc->irq_data))

And here, and I figure that this should be irqd_affinity_is_managed()

> +		return -EBUSY;
> +
> +	/*
> +	 * Deactivate the interrupt. That's required to undo
> +	 * anything an earlier activation has established.
> +	 */
> +	activated = irqd_is_activated(&desc->irq_data);
> +	if (activated)
> +		irq_domain_deactivate_irq(&desc->irq_data);
> +
> +	if (affinity->is_managed) {
> +		irqd_set(&desc->irq_data, IRQD_AFFINITY_MANAGED);
> +		irqd_set(&desc->irq_data, IRQD_MANAGED_SHUTDOWN);
> +	}
> +
> +	cpumask_copy(desc->irq_common_data.affinity, &affinity->mask);
> +
> +	/* Restore the activation state */
> +	if (activated)
> +		irq_domain_deactivate_irq(&desc->irq_data);
> +	irq_put_desc_busunlock(desc, flags);
> +	return 0;
> +}
> +
>   int __irq_set_affinity(unsigned int irq, const struct cpumask *mask, bool force)
>   {
>   	struct irq_desc *desc = irq_to_desc(irq);
> .
> 

Thanks,
John