From: Marc Zyngier <marc.zyngier@arm.com>
To: Mason <slash.tmp@free.fr>, Thomas Gleixner <tglx@linutronix.de>
Cc: Bjorn Helgaas <helgaas@kernel.org>,
Robin Murphy <robin.murphy@arm.com>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Liviu Dudau <liviu.dudau@arm.com>,
David Laight <david.laight@aculab.com>,
linux-pci <linux-pci@vger.kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Thibaud Cornic <thibaud_cornic@sigmadesigns.com>,
Phuong Nguyen <phuong_nguyen@sigmadesigns.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH v0.2] PCI: Add support for tango PCIe host bridge
Date: Tue, 11 Apr 2017 17:43:46 +0100 [thread overview]
Message-ID: <67014006-a380-9e3b-c9af-a421052cb8e0@arm.com> (raw)
In-Reply-To: <2b5eef4c-32f2-54f1-ca2f-f9426e68fb2c@free.fr>
On 11/04/17 17:26, Mason wrote:
> On 11/04/2017 17:49, Marc Zyngier wrote:
>> On 11/04/17 16:13, Mason wrote:
>>> On 27/03/2017 19:09, Marc Zyngier wrote:
>>>
>>>> Here's what your system looks like:
>>>>
>>>> PCI-EP -------> MSI Controller ------> INTC
>>>> MSI IRQ
>>>>
>>>> A PCI MSI is always edge. No ifs, no buts. That's what it is, and nothing
>>>> else. Now, your MSI controller signals its output using a level interrupt,
>>>> since you need to whack it on the head so that it lowers its line.
>>>>
>>>> There is not a single trigger, because there is not a single interrupt.
>>>
>>> Hello Marc,
>>>
>>> I was hoping you or Thomas might help clear some confusion
>>> in my mind around IRQ domains (struct irq_domain).
>>>
>>> I have read https://www.kernel.org/doc/Documentation/IRQ-domain.txt
>>>
>>> IIUC, there should be one IRQ domain per IRQ controller.
>>>
>>> I have this MSI controller handling 256 interrupts, so I should
>>> have *one* domain for all possible MSIs. Yet the Altera driver
>>> registers *two* domains (msi_domain and inner_domain).
>>>
>>> Could I make everything work with a single IRQ domain?
>>
>> No, because you have two irqchips. One that deals with the HW, and the
>> other that deals with the MSIs how they are presented to the kernel,
>> depending on the bus (PCI or something else). The fact that it doesn't
>> really drive any HW doesn't make it irrelevant.
>
> The example given in IRQ-domain.txt is
>
> Device --> IOAPIC -> Interrupt remapping Controller -> Local APIC -> CPU
>
> with an irq_domain for each interrupt controller.
Which doesn't use the generic MSI layer the way arm/arm64 do, so that's
the wrong example.
>
>
> On my system I have:
>
> PCI-EP -> MSI controller -> System INTC -> GIC -> CPU
>
> The driver for System INTC is drivers/irqchip/irq-tango.c
> I think it has only one domain.
>
> For the GIC, drivers/irqchip/irq-gic.c
> I see a call to irq_domain_create_linear()
Can we please stick to the problem at hand and not drift into other
considerations which do not matter at all?
> Is the handling of MSI different, and that is why we need
> two domains? (Sorry, I did not understand that part well.)
Let me repeat it again, then:
- You have a top-level MSI domain that is completely virtual, mapping a
virtual hwirq to the virtual interrupt. Nothing to see here.
- You have your own irqdomain, associated with your own irq_chip, which
does what it needs to do talking to the HW and allocating interrupts.
> When I looked at drivers/pci/host/pci-hyperv.c
> they seem to have a single pci_msi_create_irq_domain call,
> no call to domain_add or domain_create.
> And they have a single struct irq_chip.
Which is not using the generic MSI layer the way we do either.
>
>> You don't need to tell it anything about the number of interrupts you
>> manage. As for your private structure, you've already given it to your
>> low level domain, and there is no need to propagate it any further.
>
> My main issue is that in the ack callback, I was in the "wrong"
> domain, in that d->hwirq was not the MSI number. So I thought
> I needed a single irq_domain.
No. You need two, but you only need to manage yours.
> Is there a function to map virq to the hwirq in any domain?
Be more precise. If you want the hwirq associated with the view of a
virq in a given domain, that's the hwirq field in the corresponding
irq_data structure. Or are you after something else?
M.
--
Jazz is not dead. It just smells funny...
next prev parent reply other threads:[~2017-04-11 16:43 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-23 13:05 [RFC PATCH v0.2] PCI: Add support for tango PCIe host bridge Mason
2017-03-23 14:22 ` Marc Zyngier
2017-03-23 17:03 ` Mason
2017-03-23 23:40 ` Mason
2017-03-24 18:22 ` Marc Zyngier
2017-03-27 14:35 ` Mason
2017-03-27 14:46 ` Thomas Gleixner
2017-03-27 15:18 ` Mason
2017-03-24 18:47 ` Marc Zyngier
2017-03-27 15:53 ` Mason
2017-03-27 17:09 ` Marc Zyngier
2017-03-27 19:44 ` Mason
2017-03-27 21:07 ` Marc Zyngier
2017-03-27 22:04 ` Mason
2017-03-28 8:21 ` Marc Zyngier
2017-04-11 15:13 ` Mason
2017-04-11 15:49 ` Marc Zyngier
2017-04-11 16:26 ` Mason
2017-04-11 16:43 ` Marc Zyngier [this message]
2017-04-11 17:52 ` Mason
2017-04-12 8:08 ` Marc Zyngier
2017-04-12 9:50 ` Mason
2017-04-12 9:59 ` Marc Zyngier
2017-04-19 11:19 ` Mason
2017-04-20 8:20 ` Mason
2017-04-20 9:43 ` Marc Zyngier
2017-03-29 11:39 ` Mason
2017-03-30 11:09 ` Mason
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