linux-kernel - Re: [Patch Part2 v4 21/31] PCI/MSI: enhance PCI MSI core to support hierarchy irqdomain

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Date:	Thu, 6 Nov 2014 11:01:47 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Grant Likely <grant.likely@...aro.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Yingjoe Chen <yingjoe.chen@...iatek.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	Yijing Wang <wangyijing@...wei.com>,
	Alexander Gordeev <agordeev@...hat.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tony Luck <tony.luck@...el.com>,
	Joerg Roedel <joro@...tes.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Suravee Suthikulanit <suravee.suthikulpanit@....com>,
	x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
	linux-pci@...r.kernel.org, linux-acpi@...r.kernel.org,
	LAK <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Patch Part2 v4 21/31] PCI/MSI: enhance PCI MSI core to support
 hierarchy irqdomain

On Tue, 4 Nov 2014, Jiang Liu wrote:
> +#ifdef	CONFIG_PCI_MSI_IRQ_DOMAIN
> +static inline irq_hw_number_t
> +msi_get_hwirq(struct pci_dev *pdev, struct msi_desc *msidesc)
> +{
> +	return (irq_hw_number_t)msidesc->msi_attrib.entry_nr |
> +		PCI_DEVID(pdev->bus->number, pdev->devfn) << 11 |
> +		(pci_domain_nr(pdev->bus) & 0xFFFFFFFF) << 27;
> +}
> +
> +static int msi_domain_alloc(struct irq_domain *domain, unsigned int virq,
> +			    unsigned int nr_irqs, void *arg)
> +{
> +	int i, ret;
> +	irq_hw_number_t hwirq = arch_msi_irq_domain_get_hwirq(arg);
> +
> +	if (irq_find_mapping(domain, hwirq) > 0)
> +		return -EEXIST;
> +
> +	ret = irq_domain_alloc_irqs_parent(domain, virq, nr_irqs, arg);
> +	if (ret >= 0)
> +		for (i = 0; i < nr_irqs; i++) {
> +			irq_domain_set_hwirq_and_chip(domain, virq + i,
> +					hwirq + i, &msi_chip, (void *)(long)i);

I think msi_chip being a global unique thing is problematic. It does
not allow multi platform kernels to select a chip at boot time and it
does not allow per domain chip implementations when you have multiple
msi domains. Aside of that msi_chip is a pretty bad name for a global.

The solution is rather simple and msi is wide spread enough to justify
that.

struct irqdomain_msi_data {
       struct irq_chip       *irq_chip;
};

We make that a struct so we can accomodate for other special things
which might be domain rather than architecture specific. One
obvious use case would be to hold the arch_msi_irq_domain_get/set_hwirq
callbacks.

struct irq_domain *msi_create_irq_domain(struct irq_domain *parent,
       		  			 struct irqdomain_msi_data *data)
{
        struct irq_domain *domain;

        domain = irq_domain_add_tree(NULL, &msi_domain_ops, NULL);
        if (domain) {
                domain->parent = parent;
		domain->msi_data = data;
	}
        return domain;
}

Now the above becomes:

    	struct irq_chip *msi_chip = domain->msi_data->irq_chip;

	irq_domain_set_hwirq_and_chip(domain, virq + i,
				      hwirq + i, msi_chip, (void *)(long)i);

> +int msi_irq_domain_alloc_irqs(struct irq_domain *domain, int type,
> +			      struct pci_dev *dev, void *arg)
> +{
> +	int i, virq;
> +	struct msi_desc *msidesc;
> +	int node = dev_to_node(&dev->dev);
> +
> +	list_for_each_entry(msidesc, &dev->msi_list, list) {
> +		arch_msi_irq_domain_set_hwirq(arg, msi_get_hwirq(dev, msidesc));

The arch_xxx callbacks want to be documented. It's not obvious what
they are supposed to do.

Thanks,

	tglx
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