Messages in this thread | | | Date | Tue, 25 Oct 2016 12:39:02 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH 4/9] pinctrl: meson: allow gpio to request irq |
| |
On Tue, 25 Oct 2016, Linus Walleij wrote: > On Fri, Oct 21, 2016 at 11:06 AM, Jerome Brunet <jbrunet@baylibre.com> wrote: > > >> Isn't this usecase (also as described in the cover letter) a textbook > >> example of when you should be using hierarchical irqdomain? > >> > >> Please check with Marc et al on hierarchical irqdomains. > > > > Linus, > > Do you mean I should create a new hierarchical irqdomains in each of > > the two pinctrl instances we have in these SoC, these domains being > > stacked on the one I just added for controller in irqchip ? > > > > I did not understand this is what you meant when I asked you the > > question at ELCE. > > Honestly, I do not understand when and where to properly use > hierarchical irqdomain, even after Marc's talk at ELC-E.
Hierarchical irqdomains are used when you have several levels of interrupt hardware to deliver an interrupt.
For example on x86 we have:
device --- [IOAPIC] -- [VECTOR]
and we can have this expanded to
device --- [IOAPIC] -- [IRQ Remapping] -- [VECTOR]
and we have more things hanging off the VECTOR domain
device --- [IOAPIC] --- |--- [VECTOR] device --- [PCIMSI] ---
So with irq remapping this might look like this:
device --- [IOAPIC] --- |----------------------- device --- [PCIMSI] --- | |---[VECTOR] device --- [IOAPIC] --- | |--[IRQ Remapping]------ device --- [PCIMSI] ---
The important part is that this hierarchy deals with a single Linux virq and all parts of the hierarchy are required for setup and possibly for mask/ack/eoi.
This is different from a demultiplex interrupt
device --- [DEMUX] --- [GIC]
where the demultiplex interrupt is a different virq than the device virq. The demux interrupt chip can have a parent relation ship, which can be required to propagate information, e.g. wake on a device behind the demux must keep the gic as a wake irq as well. But it's not hierarchical in the sense of our hierarchical irq domains.
Hope that helps.
Thanks,
tglx
| |