Re: [PATCH RFC v2 03/18] irq/dev-msi: Create IR-DEV-MSI irq domain

[Jason Gunthorpe]

On Tue, Jul 21, 2020 at 09:02:35AM -0700, Dave Jiang wrote:
> From: Megha Dey <megha.dey@xxxxxxxxx>
> 
> When DEV_MSI is enabled, the dev_msi_default_domain is updated to the
> base DEV-MSI irq  domain. If interrupt remapping is enabled, we create
> a new IR-DEV-MSI irq domain and update the dev_msi_default domain to
> the same.
> 
> For X86, introduce a new irq_alloc_type which will be used by the
> interrupt remapping driver.

Why? Shouldn't this by symmetrical with normal MSI? Does MSI do this?

I would have thought you'd want to switch to this remapping mode as
part of vfio or something like current cases.

> +struct irq_domain *create_remap_dev_msi_irq_domain(struct irq_domain *parent,
> +						   const char *name)
> +{
> +	struct fwnode_handle *fn;
> +	struct irq_domain *domain;
> +
> +	fn = irq_domain_alloc_named_fwnode(name);
> +	if (!fn)
> +		return NULL;
> +
> +	domain = msi_create_irq_domain(fn, &dev_msi_ir_domain_info, parent);
> +	if (!domain) {
> +		pr_warn("failed to initialize irqdomain for IR-DEV-MSI.\n");
> +		return ERR_PTR(-ENXIO);
> +	}
> +
> +	irq_domain_update_bus_token(domain, DOMAIN_BUS_PLATFORM_MSI);
> +
> +	if (!dev_msi_default_domain)
> +		dev_msi_default_domain = domain;
> +
> +	return domain;
> +}

What about this code creates a "remap" ? ie why is the function called
"create_remap" ?

> diff --git a/include/linux/msi.h b/include/linux/msi.h
> index 1da97f905720..7098ba566bcd 100644
> +++ b/include/linux/msi.h
> @@ -378,6 +378,9 @@ void *platform_msi_get_host_data(struct irq_domain *domain);
>  void platform_msi_write_msg(struct irq_data *data, struct msi_msg *msg);
>  void platform_msi_unmask_irq(struct irq_data *data);
>  void platform_msi_mask_irq(struct irq_data *data);
> +
> +int dev_msi_prepare(struct irq_domain *domain, struct device *dev,
> +                           int nvec, msi_alloc_info_t *arg);

I wonder if this should use the popular #ifdef dev_msi_prepare scheme
instead of a weak symbol?

Jason