From: Marc Zyngier <marc.zyngier@arm.com>
To: Mason <slash.tmp@free.fr>
Cc: Sebastian Frias <sf84@laposte.net>,
Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
Grygorii Strashko <grygorii.strashko@ti.com>,
Mans Rullgard <mans@mansr.com>
Subject: Re: Using irq-crossbar.c
Date: Sun, 12 Jun 2016 11:00:48 +0100 [thread overview]
Message-ID: <20160612110048.3dd5ea17@arm.com> (raw)
In-Reply-To: <575C304F.2070303@free.fr>
On Sat, 11 Jun 2016 17:37:51 +0200
Mason <slash.tmp@free.fr> wrote:
> On 11/06/2016 11:58, Marc Zyngier wrote:
>
> > Mason wrote:
> >
> >> I think Sebastian is even more baffled by the DT mess
> >> (sorry, intricacies) than I am.
> >
> > This mess is what has saved us from the apocalypse 5 years ago, and
> > describing a complex system is not easy (what a surprise...).
>
> The problem with some Linux APIs is that they're logical and obvious
> to people who've been using them for years. For newcomers, it's not
> always so obvious.
>
> In this specific instance, the problem statement seems rather simple,
> on the surface. An interrupt controller, X=0..127 lines in, Y=0..23
> lines out (connected to GIC interrupt lines 0..23) and "all" we need
> is a way to map Xs to Ys.
>
> As a first order approximation, it's enough to map all Xs to 0.
> And provide a way for the kernel to check the registers containing
> the bit-vectors indicating which interrupt(s) fired.
If that's what your hardware is, then you are taking the wrong
approach. The irq-crossbar driver does not do that at all: it has x
inputs and y outputs, but connects exactly *one input to one output*.
No multiplexing.
And the hierarchical domain infrastructure enforces a similar property:
a Linux interrupt is dealt with at each level of the hierarchy without
multiplexing: the "irq" is the same, while the "hwirq" varies to
reflect the "input pin" for a given interrupt controller.
In your particular case, you have an evolved chained interrupt
controller, and nothing else.
>
> > If you just want to apply recipes without understanding the underlying
> > constraints, you're in for a lot of pain.
>
> For example, the IRQ driver for Tango3/4 calls
>
> irq_find_mapping
> generic_handle_irq
> irq_desc_get_handler_data
> irq_desc_get_chip
> chained_irq_enter/chained_irq_exit
> irq_setup_alt_chip
> irq_get_domain_generic_chip
> irq_domain_add_linear
> irq_alloc_domain_generic_chips
> irq_set_chained_handler
> irq_set_handler_data
>
> Taking irq_find_mapping, I see that there's a short comment in
> kernel/irq/irqdomain.c
>
> /**
> * irq_find_mapping() - Find a linux irq from an hw irq number.
> * @domain: domain owning this hardware interrupt
> * @hwirq: hardware irq number in that domain space
> */
>
> Is this Doxygen format? Is there a make target to generate
> some documentation?
Try "make help".
>
> Other relevant resources, for my own reference:
>
> https://www.kernel.org/doc/Documentation/IRQ-domain.txt
> https://stackoverflow.com/questions/34371352/what-are-linux-irq-domains-why-are-they-needed
> https://community.nxp.com/thread/332183
>
> Are there other important kernel documentation?
>
> >> The base file he was referring to is:
> >>
> >> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/tango4-common.dtsi
> >
> > I know which file that is, it is mentioned in the diff. I was merely
> > trying to point out the glaring mistakes that could be enough for a
> > interrupt controller hierarchy to be completely non-functional:
>
> Only the name of the file was provided, not the path. I was not aware
> that you already knew where to find it. I made no claim whatsoever on
> the implementation. In fact, I agree with everything Lennart wrote.
>
> > - Your crossbar doesn't have a #interrupt-cells property. How do you
> > expect the interrupt specifiers to be interpreted?
>
> Why do "fundamental" DT properties start with hash?
Because # is a shorthand for "number of".
>
> > - You've changed the default interrupt controller to be your crossbar.
> > Which means that all the sub-nodes are inheriting it. Have you
> > checked that this was valid for all of these nodes?
>
> I'm not sure I follow. All platform interrupts flow into the platform
> controller. Maybe other platforms have more complex setups, with
> several cascaded controllers?
Most embedded platforms do.
M.
--
Jazz is not dead. It just smells funny.
next prev parent reply other threads:[~2016-06-12 10:00 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-10 15:37 Using irq-crossbar.c Sebastian Frias
2016-06-10 16:05 ` Marc Zyngier
2016-06-10 19:36 ` Mason
2016-06-11 9:58 ` Marc Zyngier
2016-06-11 15:37 ` Mason
2016-06-12 10:00 ` Marc Zyngier [this message]
2016-06-12 13:50 ` Mason
2016-06-13 7:58 ` Marc Zyngier
2016-06-13 14:04 ` Lennart Sorensen
2016-06-13 14:57 ` Sebastian Frias
2016-06-13 15:42 ` Lennart Sorensen
2016-06-13 15:49 ` Mason
2016-06-13 15:57 ` Marc Zyngier
2016-06-13 17:55 ` Lennart Sorensen
2016-06-13 15:15 ` Sebastian Frias
2016-06-13 16:26 ` Marc Zyngier
2016-06-13 15:46 ` Sebastian Frias
2016-06-13 16:24 ` Marc Zyngier
2016-06-14 16:37 ` Sebastian Frias
2016-06-14 16:39 ` Sebastian Frias
2016-06-16 12:39 ` Sebastian Frias
2016-06-21 10:18 ` Marc Zyngier
2016-06-21 11:03 ` Sebastian Frias
2016-06-21 12:41 ` Marc Zyngier
2016-06-21 15:29 ` Sebastian Frias
2016-06-13 17:59 ` Lennart Sorensen
2016-06-10 16:06 ` Lennart Sorensen
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