linux-kernel - Re: [RFC PATCH v0.2] PCI: Add support for tango PCIe host bridge

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Date:   Tue, 11 Apr 2017 17:13:35 +0200
From:   Mason <slash.tmp@...e.fr>
To:     Marc Zyngier <marc.zyngier@....com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Liviu Dudau <liviu.dudau@....com>,
        David Laight <david.laight@...lab.com>,
        linux-pci <linux-pci@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Thibaud Cornic <thibaud_cornic@...madesigns.com>,
        Phuong Nguyen <phuong_nguyen@...madesigns.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v0.2] PCI: Add support for tango PCIe host bridge

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?

I'm confused by the sequence:

  irq_dom = irq_domain_create_linear(fwnode, MSI_COUNT, &msi_dom_ops, pcie);
  msi_dom = pci_msi_create_irq_domain(fwnode, &msi_domain_info, irq_dom);

It seems I should be able to call only pci_msi_create_irq_domain...
And the parent of the MSI controller is given in the DT.

I'm not quite sure how I tell pci_msi_create_irq_domain how many
MSIs it's supposed to manage. Nor how I pass my private struct.

I will keep looking.

Regards.