Re: [patch 02/33] genirq/msi: Provide struct msi_parent_ops

[Jason Gunthorpe <jgg@nvidia.com>]

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