linux-kernel - Re: [patch 02/33] genirq/msi: Provide struct msi_parent

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Date:   Wed, 16 Nov 2022 14:57:34 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Marc Zyngier <maz@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dave Jiang <dave.jiang@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Ashok Raj <ashok.raj@...el.com>, Jon Mason <jdmason@...zu.us>,
        Allen Hubbe <allenbh@...il.com>,
        "Ahmed S. Darwish" <darwi@...utronix.de>,
        Reinette Chatre <reinette.chatre@...el.com>
Subject: Re: [patch 02/33] genirq/msi: Provide struct msi_parent_ops

On Fri, Nov 11, 2022 at 02:58:14PM +0100, Thomas Gleixner wrote:
> +/**
> + * msi_parent_init_dev_msi_info - Delegate initialization of device MSI info to parent domain
> + * @dev:		The device for which the domain should be created
> + * @domain:		The domain which delegates
> + * @real_parent:	The real parent domain of the to be initialized MSI domain
> + * @info:		The MSI domain info to initialize
> + *
> + * Return: true on success, false otherwise
> + *
> + * This is the most complex problem of per device MSI domains and the
> + * underlying interrupt domain hierarchy:
> + *
> + * The device domain to be initialized requests the broadest feature set
> + * possible and the underlying domain hierarchy puts restrictions on it.
> + *
> + * That's working perfectly fine for a strict parent->device model, but it
> + * falls apart with a root_parent->real_parent->device chain because the

This language hurt my brain :)

> +bool msi_parent_init_dev_msi_info(struct device *dev, struct irq_domain *domain,
> +				  struct irq_domain *real_parent, struct msi_domain_info *info)

'real_parent' is global IRQ_DOMAIN_FLAG_MSI_PARENT of the dev for
which we are constructing a msi_domain_info to create a child aka
IRQ_DOMAIN_FLAG_MSI_DEVICE?

'domain' is the current step in the hierarchy as we walk up the ops
pointers?

Maybe:

@child_info: The MSI domain info of the IRQ_DOMAIN_FLAG_MSI_DEVICE
             domain to be created
@parent_domain: The IRQ_DOMAIN_FLAG_MSI_PARENT domain for the child to
                be created
@domain: The domain in the hierarchy this op is being called on

And perhaps it would be a bit clearer to put the parent_domain inside
the msi_domain_info, which is basically acting as an argument bundle
for a future allocation call?

Jason