linux-kernel - irqdomain API: how to set affinity of parent irq of chained irqs?

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Date:   Mon, 2 May 2022 10:21:37 +0200
From:   Marek Behún <kabel@...nel.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        pali@...nel.org
Subject: irqdomain API: how to set affinity of parent irq of chained irqs?

Dear Marc, Thomas,

we have encountered the following problem that can hopefully be put
some light onto: What is the intended way to set affinity (and possibly
other irq attributes) of parent IRQ of chained IRQs, when using the
irqdomain API?

We are working on a driver that
- registers an irqchip and adds an irqdomain
- calls irq_set_chained_handler_and_data(parent_irq, handler)
  where handler triggers handling of child IRQs
- but since parent_irq isn't requested for with request_thread_irq(),
  it does not show up in proc/sysfs, only in debugfs
- the HW does not support setting affinity for the chained IRQs, only 
  the parent (which comes from a GIC chip)

The problem is that he parent IRQ, as mentioned in the third point, does
not show up in proc/sysfs.

Is there some precedent for this?

Thank you.

Marek