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: Mon, 13 Jun 2016 08:58:33 +0100 [thread overview]
Message-ID: <575E67A9.9020003@arm.com> (raw)
In-Reply-To: <575D689E.9080205@free.fr>
On 12/06/16 14:50, Mason wrote:
> On 12/06/2016 12:00, Marc Zyngier wrote:
>
>> Mason wrote:
>>
>>> 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.
>
> Connecting one input to one output is possible iff x=y right?
> (In other words, a bijection.)
It is *always* possible to connect anything to anything else. You were
assuming that this particular driver was fitting your particular case,
and it is obvious that it is not (iow: the crossbar transformation
cannot be surjective).
>> 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.
>
> Is it possible to support such an "evolved chained intc" through DT only,
> or does it require a few function calls from driver code?
There is no such thing as "DT only". You will have to do some actual
irqchip development.
>>>> - 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.
>
> My imagination is lacking, I don't see why it needs to be more
> complex than N platform input lines, and M output lines feeding
> into the GIC (with M <= N)
It is not more complex. It is different.
M.
--
Jazz is not dead. It just smells funny...
next prev parent reply other threads:[~2016-06-13 7:58 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
2016-06-12 13:50 ` Mason
2016-06-13 7:58 ` Marc Zyngier [this message]
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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