linux-kernel - Re: [patch 24/33] PCI/MSI: Provide prepare

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Message-ID: <20221116202619.GA1134246@bhelgaas>
Date:   Wed, 16 Nov 2022 14:26:19 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
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>,
        Jason Gunthorpe <jgg@...lanox.com>,
        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 24/33] PCI/MSI: Provide prepare_desc() MSI domain op

On Fri, Nov 11, 2022 at 02:58:49PM +0100, Thomas Gleixner wrote:
> Dynamic MSI-X vector allocation post MSI-X allows to allocate vectors at a
> given index or at any free index in the available table range.

Is "post MSI-X" missing something?  "post MSI-X enablement" or
something?

> The latter
> requires that the core code selects the index at descriptor allocation time.
> 
> This requires that the PCI/MSI-X specific setup of the MSI-X descriptor,
> which is partially depending on the chosen index happens after allocation.

Is there a comma missing after "index"?  I.e., setup of the descriptor
partially depends on the chosen index?  And the above requires that
setup happens after allocation?

> Implement the prepare_desc() op in the PCI/MSI-X specific msi_domain_ops
> which is invoked before the core interrupt descriptor and the associated
> Linux interrupt number is allocated. That callback is also provided for the
> upcoming PCI/IMS implementations so the implementation specific interrupt
> domain can do their domain specific initialization of the MSI descriptors.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>

> ---
>  drivers/pci/msi/irqdomain.c |    9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> --- a/drivers/pci/msi/irqdomain.c
> +++ b/drivers/pci/msi/irqdomain.c
> @@ -202,6 +202,14 @@ static void pci_unmask_msix(struct irq_d
>  	pci_msix_unmask(irq_data_get_msi_desc(data));
>  }
>  
> +static void pci_msix_prepare_desc(struct irq_domain *domain, msi_alloc_info_t *arg,
> +				  struct msi_desc *desc)
> +{
> +	/* Don't fiddle with preallocated MSI descriptors */
> +	if (!desc->pci.mask_base)
> +		msix_prepare_msi_desc(to_pci_dev(desc->dev), desc);
> +}
> +
>  static struct msi_domain_template pci_msix_template = {
>  	.chip = {
>  		.name			= "PCI-MSIX",
> @@ -212,6 +220,7 @@ static struct msi_domain_template pci_ms
>  	},
>  
>  	.ops = {
> +		.prepare_desc		= pci_msix_prepare_desc,
>  		.set_desc		= pci_device_domain_set_desc,
>  	},
>  
>