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

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Date:   Tue, 21 Jul 2020 13:21:04 -0300
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     Dave Jiang <dave.jiang@...el.com>
Cc:     vkoul@...nel.org, megha.dey@...el.com, maz@...nel.org,
        bhelgaas@...gle.com, rafael@...nel.org, gregkh@...uxfoundation.org,
        tglx@...utronix.de, hpa@...or.com, alex.williamson@...hat.com,
        jacob.jun.pan@...el.com, ashok.raj@...el.com, yi.l.liu@...el.com,
        baolu.lu@...el.com, kevin.tian@...el.com, sanjay.k.kumar@...el.com,
        tony.luck@...el.com, jing.lin@...el.com, dan.j.williams@...el.com,
        kwankhede@...dia.com, eric.auger@...hat.com, parav@...lanox.com,
        dave.hansen@...el.com, netanelg@...lanox.com, shahafs@...lanox.com,
        yan.y.zhao@...ux.intel.com, pbonzini@...hat.com,
        samuel.ortiz@...el.com, mona.hossain@...el.com,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-pci@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH RFC v2 03/18] irq/dev-msi: Create IR-DEV-MSI irq domain

On Tue, Jul 21, 2020 at 09:02:35AM -0700, Dave Jiang wrote:
> From: Megha Dey <megha.dey@...el.com>
> 
> 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