linux-kernel - RE: [patch V2 13/33] x86/apic/vector: Provide MSI parent domain

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Date:   Wed, 23 Nov 2022 14:42:10 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     "x86@...nel.org" <x86@...nel.org>, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        "linux-pci@...r.kernel.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>,
        Jason Gunthorpe <jgg@...lanox.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        "Raj, Ashok" <ashok.raj@...el.com>, Jon Mason <jdmason@...zu.us>,
        Allen Hubbe <allenbh@...il.com>
Subject: RE: [patch V2 13/33] x86/apic/vector: Provide MSI parent domain

On Wed, Nov 23 2022 at 08:16, Kevin Tian wrote:
>> From: Thomas Gleixner <tglx@...utronix.de>
>> Sent: Monday, November 21, 2022 10:38 PM
>> 
>> +bool pci_dev_has_default_msi_parent_domain(struct pci_dev *dev)
>> +{
>> +	struct irq_domain *domain = dev_get_msi_domain(&dev->dev);
>> 
>> -int pci_msi_prepare(struct irq_domain *domain, struct device *dev, int nvec,
>> -		    msi_alloc_info_t *arg)
>> +	if (!domain)
>> +		domain = dev_get_msi_domain(&dev->bus->dev);
>> +	if (!domain)
>> +		return false;
>> +
>> +	return domain == x86_vector_domain;
>
> the function name is about parent domain but there is no check on
> the parent flag. Probably just remove 'parent'?

No. This checks whether the device has the default MSI parent domain,
which _IS_ the vector domain.

I really don't have to check whether the vector domain has the MSI
parent flag set or not. It _IS_ set. If that gets lost later then the
result of the above function is the least of our problems.

>> +/**
>> + * x86_init_dev_msi_info - Domain info setup for MSI domains
>> + * @dev:		The device for which the domain should be created
>> + * @domain:		The (root) domain providing this callback
>
> what is the purpose of '(root)'? it's also used by intermediate domain
> i.e. IR.

It _can_ be used, yes. But the way I implemented IR MSI parents it is
not used by it.

>> +
>> +	/*
>> +	 * Mask out the domain specific MSI feature flags which are not
>> +	 * supported by the real parent.
>> +	 */
>> +	info->flags			&= pops->supported_flags;
>> +	/* Enforce the required flags */
>> +	info->flags			|=
>> X86_VECTOR_MSI_FLAGS_REQUIRED;
>> +
>> +	/* This is always invoked from the top level MSI domain! */
>> +	info->ops->msi_prepare		= x86_msi_prepare;
>> +
>> +	info->chip->irq_ack		= irq_chip_ack_parent;
>> +	info->chip->irq_retrigger	= irq_chip_retrigger_hierarchy;
>> +	info->chip->flags		|= IRQCHIP_SKIP_SET_WAKE |
>> +					   IRQCHIP_AFFINITY_PRE_STARTUP;
>
> Above are executed twice for both IR and vector after next patch comes.
> Could skip it for IR.

How so?

+static const struct msi_parent_ops dmar_msi_parent_ops = {
+	.supported_flags	= X86_VECTOR_MSI_FLAGS_SUPPORTED | MSI_FLAG_MULTI_PCI_MSI,
+	.prefix			= "IR-",
+	.init_dev_msi_info	= msi_parent_init_dev_msi_info,
+};

IR delegates the init to its parent domain, i.e. the vector domain. So
there is no double invocation.

Thanks,

        tglx